CRAM by MRM

POSSIBLY EFFECTIVE

• Age-related cognitive decline. Oral acetyl-L-carnitine may improve age-related cognitive decline. Details: Clinical research shows that taking acetyl-L-carnitine 1500-2000 mg daily for 3 months seems to improve some measures of cognitive function and memory in elderly people with age-related cognitive decline (42,3600,3601).
• Age-related fatigue. Oral acetyl-L-carnitine may improve age-related physical and mental fatigue. Details: One clinical trial shows that taking acetyl-L-carnitine 2 grams twice daily for 180 days reduces physical fatigue by 52% and mental fatigue by 43%, compared with only 4% and 8%, respectively, for elderly patients taking placebo. Fatigue after exercise is also reduced by 51% in those taking acetyl-L-carnitine, compared with only 4% in those taking placebo (58375).
• Alcohol use disorder. Intravenous acetyl-L-carnitine may reduce cravings and other symptoms of withdrawal during alcohol detoxification. It is unclear if oral acetyl-L-carnitine is beneficial for managing withdrawal or complications of alcohol use disorder. Details: Clinical research in adults with alcohol use disorder who are in withdrawal shows that acetyl-L-carnitine 1-3 grams daily, administered as a slow intravenous infusion over 3-4 hours for 10 days, followed by 3 grams daily orally for an additional 80 days, improves cravings, the inability to feel pleasure (anhedonia), and melancholic symptoms and increases the time to the first drink when compared with placebo. However, most symptom improvement appears to occur during the first week, so it is unclear if taking acetyl-L-carnitine 3 grams daily orally for an additional 80 days is beneficial (90766,90767). One small clinical trial in adults with chronic alcohol use disorder and cognitive impairment shows that taking acetyl-L-carnitine 2 grams daily for 90 days seems to improve memory and visuospatial capacity when compared with placebo (1589).
• Alzheimer disease. Oral acetyl-L-carnitine may slow the progression of Alzheimer disease and improve some measures of cognitive function. Details: Clinical research shows that taking acetyl-L-carnitine 1.5-3 grams daily for 3-12 months might slow the rate of Alzheimer disease progression and improve memory, some measures of cognitive function, and behavioral performance. It is more likely to show some effect in those with early-onset Alzheimer disease who are less than 66 years of age and have a faster rate of disease progression and mental decline (1594,1595,1596,1597,1598,1599,9105,10391). It is unclear how acetyl-L-carnitine compares with prescription medications.
• Depression. Oral acetyl-L-carnitine may reduce symptoms of depression, with comparable effects to conventional antidepressants, in patients with dysthymia and depression. It may be most effective in elderly patients and at higher doses. Details: Several clinical trials addressing the use of acetyl-L-carnitine in elderly patients with dysthymia and depression have been conducted (3602,3603,3604). A meta-analysis of these and other studies, all conducted in Europe, shows that taking acetyl-L-carnitine 1-4 grams daily for 3-24 weeks moderately reduces depressive symptoms when compared with placebo, and appears to have similar effects as conventional antidepressants. Acetyl-L-carnitine seems to be most effective when used at higher dosages. Duration of follow-up and baseline symptoms do not appear to influence results (95065).
• Diabetic neuropathy. Oral acetyl-L-carnitine may reduce pain in patients with diabetic neuropathy when taken at doses of at least 2-3 grams daily. It is unclear if oral acetyl-L-carnitine can improve nerve conduction velocity in these patients. Details: Although most clinical research evaluating acetyl-L-carnitine for use in diabetic neuropathy has shown benefit, this evidence is of overall low quality. A meta-analysis shows that taking acetyl-L-carnitine 2-3 grams daily for up to 12 months modestly reduces pain scores by about 15 points on a 100-point visual analog scale, while lower doses of 1.5 grams daily improve pain scores to a similar extent as placebo. Some research included in this analysis shows that acetyl-L-carnitine seems to increase nerve fibers, regenerate nerve fiber clusters, and improve vibratory sensations. In two studies, vibration sensation improved after 12 months when compared with placebo, but numerical data are lacking (102126). Other clinical research shows that taking acetyl-L-carnitine 1000 mg 2-3 times daily decreases pain within 6 months. Acetyl-L-carnitine seems to be most effective for reducing pain in patients with a shorter duration of diabetes and in patients with poorly controlled type 2 diabetes. Some research shows that taking acetyl-L-carnitine 500 mg (Liaoning Haisike Pharmaceutical Co. Ltd.) three times daily for 24 weeks is as effective as methylcobalamin 0.5 mg three times daily for improving electrophysiological parameters and symptoms as measured by the Neuropathy Disability Score (95067,102126). However, research on the use of acetyl-L-carnitine to improve nerve conduction velocity in patients with diabetic neuropathy is conflicting (1593,12743,12753,13007,95067).
• Male infertility. Oral acetyl-L-carnitine, taken in combination with L-carnitine, may increase sperm motility in males with infertility. It is unclear if oral acetyl-L-carnitine alone can improve sperm function or pregnancy outcomes. Details: Although some research disagrees (111861), taking acetyl-L-carnitine in combination with L-carnitine, usually in doses of 1 gram and 2 grams, respectively, daily for 3-6 months seems to increase sperm motility in males with infertility of various etiologies. The evidence related to the effect of this combination on sperm count and morphology is mixed (12352,58182,58194,58469,101560,107394,111459,111890). However, it is unclear if taking L-carnitine increases the odds of pregnancy. One meta-analysis of randomized controlled trials shows that taking these carnitines in combination increases the odds of pregnancy by 3.7-fold over placebo. However most clinical research investigating the effect of L-carnitine alone or with acetyl L-carnitine on pregnancy rates disagrees (12352,58182,101560,111861,111459). Taking acetyl-L-carnitine 500 mg and L-carnitine 1 gram twice daily after taking nonsteroidal anti-inflammatory drugs for 2 months seems to increase sperm count and motility in those with abacterial prostatovesiculoepididymitis, an inflammation of the prostate gland, seminal vesicles, and epididymis (9791). Acetyl-L-carnitine has also been evaluated in combination with other ingredients. One study shows that taking acetyl-L-carnitine 50 mg in combination with L-carnitine 150 mg, L-arginine 1660 mg, and Panax ginseng 200 mg daily for 3 months increases sperm motility and sexual satisfaction in those with asthenospermia when compared with no treatment (32189). Another small clinical trial shows that taking this combination along with prulifloxacin 600 mg daily for 6 months improves sperm concentration and motility when compared with treatment with prulifloxacin alone in patients with chronic prostatitis due to Chlamydia trachomatis infection (59006). Other small and preliminary Iclinical studies have investigated the effects of a specific combination product providing acetyl-L-carnitine 500 mg twice daily for 6 months, along with L-carnitine, coenzyme Q10, selenium, zinc, vitamin C, folic acid, vitamin B12, and citric acid (Proxeed Plus). Taking this combination product has been shown to improve measures of sperm quality such as sperm count, sperm concentration, total motility, and progressive motility when compared to baseline. The effect on sperm volume and morphology is unclear. Most research has been conducted in patients with oligoasthenozoospermia, although some benefit has also been shown in patients with varicocele-related infertility, especially those with more severe varicocele (102017,107395,111296). The validity of these findings is limited by the lack of comparator group. Also, it is unclear if these effects are due to L-carnitine, other ingredients, or the combination.

POSSIBLY INEFFECTIVE

• Chemotherapy-induced peripheral neuropathy. The evidence related to the effect of oral acetyl-L-carnitine on symptoms of chemotherapy-induced peripheral neuropathy is mixed. Some research shows that it may actually worsen symptoms. Details: High quality clinical research in females treated with taxane-based therapy for early-stage breast cancer shows that taking acetyl-L-carnitine 1000 mg three times daily for 24 weeks does not improve symptoms of neuropathy when compared with placebo. In fact, acetyl-L-carnitine treatment may actually make symptoms worse in some patients, with worsened symptoms persisting for up to at least 2 years (90758,96938,111882). Also, a small clinical trial in patients with multiple myeloma receiving bortezomib, doxorubicin, and dexamethasone shows that taking acetyl-L-carnitine 1.5 grams daily does not reduce symptoms of peripheral neuropathy when compared with not taking acetyl-L-carnitine (90756). A small clinical trial in patients with ovarian cancer or castration-resistant prostate cancer receiving sagopilone shows that taking acetyl-L-carnitine 1000 mg every three days appears to reduce the more severe symptoms of peripheral neuropathy; however, the overall incidence or duration of peripheral neuropathy is not reduced when compared with placebo (90757). Some research disagrees. One clinical trial in patients with taxoid-related neuropathy shows that taking acetyl-L-carnitine3 grams daily for 8 weeks modestly improves the severity of neuropathy by at last one grade in 51% of patients compared with 24% of those taking placebo. Functional improvement was also modestly improved (111862). Based on the available research, the American Society of Clinical Oncology strongly discourages the use of acetyl-L-carnitine for the prevention of chemotherapy-induced peripheral neuropathy, noting that the harms outweigh the potential benefits (104168).

INSUFFICIENT RELIABLE EVIDENCE to RATE

• Age-related testosterone deficiency. Oral acetyl-L-carnitine has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: One clinical study in older males shows that taking acetyl-L-carnitine 2 grams, in combination with propionyl-L-carnitine 2 grams, daily for 6 months seems to attenuate symptoms of androgen decline. The combination appears to be similar to testosterone for improving sexual dysfunction, depression, and fatigue (12353). It is unclear if these findings are due to acetyl-L-carnitine, propionyl-L-carnitine, or the combination.
• Aging skin. Although there has been interest in using oral acetyl-L-carnitine for aging skin, there is insufficient reliable information about the clinical effects of acetyl-L-carnitine for this purpose.
• Amenorrhea. Although there has been interest in using oral acetyl-L-carnitine for amenorrhea, there is insufficient reliable information about the clinical effects of acetyl-L-carnitine for this purpose.
• Amyotrophic lateral sclerosis (ALS, Lou Gehrig's disease). It is unclear if oral acetyl-L-carnitine is beneficial in patients with ALS. Details: One small clinical trial in patients with ALS shows that taking acetyl-L-carnitine 1000 mg three times daily for 48 weeks, along with riluzole 50 mg twice daily, reduces the number of patients who lose self-sufficiency by about 17%, increases patient survival by a median of 23 months, and improves some measures of physical function when compared with riluzole alone (90755).
• Antiretroviral toxic neuropathy. Small clinical studies suggest that oral acetyl-L-carnitine may modestly improve symptoms in patients with antiretroviral toxic neuropathy. It is unclear if intramuscular or intravenous acetyl-L-carnitine is beneficial in patients with this condition. Details: Small clinical trials show that taking acetyl-L-carnitine 1000-1500 mg twice daily for up to 33 months might relieve symptoms of distal symmetrical polyneuropathy caused by antiretroviral treatment in HIV-positive patients (12745,58342). Also, a small, uncontrolled clinical study shows that intramuscular or intravenous administration of acetyl-L-carnitine 500-1000 mg daily for 3 weeks reduces pain intensity when compared to baseline in some HIV-positive patients receiving antiretroviral therapy (12747). However, another clinical study shows that intramuscular acetyl-L-carnitine 500 mg twice daily for 14 days does not reduce pain when compared with placebo (58342).
• Athletic performance. Although there has been interest in using oral acetyl-L-carnitine for athletic performance, there is insufficient reliable information about the clinical effects of acetyl-L-carnitine for this purpose.
• Attention deficit-hyperactivity disorder (ADHD). Small clinical trials suggest that oral acetyl-L-carnitine is not beneficial in children with ADHD. Details: One small clinical trial in children and adolescents with ADHD shows that taking acetyl-L-carnitine 1-3 grams daily, based on body weight, in two divided doses along with methylphenidate 20-30 mg daily for 3 weeks does not reduce symptoms of ADHD when compared with methylphenidate alone (90754). Based on this and another small trial, Guidelines from The World Federation of Societies of Biological Psychiatry (WFSBP) and Canadian Network for Mood and Anxiety Treatments (CANMAT) Taskforce state that acetyl-L-carnitine in doses of 1-3 grams daily is not recommended for adjunctive or monotherapy use for ADHD in children (110318).
• Bell palsy. Although there has been interest in using oral acetyl-L-carnitine for Bell palsy, there is insufficient reliable information about the clinical effects of acetyl-L-carnitine for this purpose.
• Bipolar disorder. Oral acetyl-L-carnitine has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: One small clinical trial in patients with type I or type II bipolar disorder shows that taking acetyl-L-carnitine 1000 mg plus alpha-lipoic acid 600 mg up to three times daily for 12 weeks does not improve depression when compared with placebo (90441).
• Cancer-related fatigue. Although there has been interest in using oral acetyl-L-carnitine for cancer-related fatigue, there is insufficient reliable information about the clinical effects of acetyl-L-carnitine for this purpose.
• Carpal tunnel syndrome. It is unclear if oral acetyl-L-carnitine is beneficial in patients undergoing surgery for carpal tunnel syndrome. Details: A small clinical study in adults undergoing carpal tunnel release surgery shows that taking acetyl-L-carnitine 3000 mg daily for 2 months postoperatively does not improve nerve regeneration or functional recovery when compared with placebo (100349). However, this study may have been inadequately powered to detect a difference between groups. Acetyl-L-carnitine has also been investigated in combination with other ingredients. In patients with mild to moderate symptoms awaiting carpal tunnel release, preliminary clinical research shows that taking acetyl-L-carnitine as part of a multi-ingredient formulation for 60 days reduces pain by 31%, but does not improve function, when compared with no treatment. The formulation provided a total of 600 mg twice daily of acetyl-L-carnitine with alpha-lipoic acid, phosphatidylserine, curcumin, thiamine, riboflavin, and vitamins C, E, B6, and B12 (111702).
• Cataracts. Although there has been interest in using oral acetyl-L-carnitine for cataracts, there is insufficient reliable information about the clinical effects of acetyl-L-carnitine for this purpose.
• Chronic fatigue syndrome (CFS). It is unclear if oral acetyl-L-carnitine is beneficial in patients with CFS. Details: Preliminary clinical research in patients with CFS shows that taking acetyl-L-carnitine 2 grams daily for 6 months improves general fatigue in up to 59% of patients when compared with baseline. The combination of acetyl-L-carnitine and propionyl-L-carnitine appears to be less effective than either supplement alone, with only 37% of patients taking this combination achieving improvement when compared with baseline (11788).
• Diabetes. It is unclear if oral acetyl-L-carnitine improves glycemic control in people with type 2 diabetes. Details: Clinical research in patients with type 2 diabetes, hypertension, and dyslipidemia shows that taking acetyl-L-carnitine 1 gram twice daily for 6 months does not improve blood glucose levels, glycated hemoglobin, fasting insulin levels, insulin resistance, or glucose disposal rate when compared with placebo. Most patients were already taking one or more antidiabetes drug, as well as medication for hypertension and dyslipidemia (96937). It is unclear if acetyl-L-carnitine improves glycemic profile in patients with uncontrolled diabetes.
• Down syndrome. Although there has been interest in using oral acetyl-L-carnitine for Down syndrome, there is insufficient reliable information about the clinical effects of acetyl-L-carnitine for this purpose.
• Dyslipidemia. It is unclear if oral acetyl-L-carnitine reduces lipid levels in adults with dyslipidemia. Details: Clinical research in patients with dyslipidemia, type 2 diabetes, and hypertension shows that taking acetyl-L-carnitine 1 gram twice daily for 6 months does not improve cholesterol, triglycerides, or lipoprotein(a) levels when compared with placebo. All patients were taking statins prior to treatment with acetyl-L-carnitine, and most were receiving medication for hypertension and diabetes (96937). It is unclear if acetyl-L-carnitine is beneficial in patients not taking statins.
• Fibromyalgia. It is unclear if oral and/or intramuscular acetyl-L-carnitine can improve symptoms of fibromyalgia. Details: One clinical study in patients with fibromyalgia shows that taking acetyl-L-carnitine 1000 mg daily orally plus acetyl-L-carnitine 500 mg daily intramuscularly for 2 weeks, followed by acetyl-L-carnitine 1500 mg daily orally for 8 weeks, reduces muscle pain and improves mood, general health, and quality of life when compared with placebo (90768). A smaller clinical study in patients with fibromyalgia shows that taking acetyl-L-carnitine 500 mg three times daily for 12 weeks improves quality of life (physical) scores and symptoms of depression, but not pain, anxiety, or quality of life (mental) scores when compared with baseline (90761). The validity of these findings is limited by the lack of a comparator group. Acetyl-L-carnitine has also been investigated in combination with other ingredients. Clinical research shows that taking acetyl-L-carnitine 500 mg and palmitoylethanolamide (PEA) 600 mg twice daily for 12 weeks increases the proportion of patients with at least a 30% reduction in pain by 86% when compared with not taking this combination. There was also a modest improvement in the overall assessment of status. All patients were on stable treatment with duloxetine and pregabalin for 3 months prior to the initiation of acetyl-L-carnitine and PEA, and this treatment continued throughout the study (111901).
• Fragile X syndrome. Small clinical studies suggest that oral acetyl-L-carnitine is not beneficial in children with fragile X syndrome. Details: Two small clinical studies in children with fragile X syndrome shows that acetyl-L-carnitine 20-50 mg/kg daily for one year does not improve intellectual function when compared with placebo. Also, while it may reduce hyperactive behavior in these patients based on parent assessment, it does not appear to reduce hyperactive behavior based on teacher assessment (9956,93063).
• Frailty. It is unclear if oral acetyl-L-carnitine prevents frailty. Details: Clinical research in pre-frail older adults shows that taking acetyl-L-carnitine 1.5 grams twice daily for 3 months modestly improves cognition and the distance walked in 6 minutes when compared with taking placebo (111889). It is unclear whether taking acetyl-L-carnitine is beneficial for frailty treatment or prevention.
• Hepatic encephalopathy. Small clinical studies suggest that oral acetyl-L-carnitine may not improve quality of life or fatigue in patients with hepatic encephalopathy due to cirrhosis. Details: The benefits of acetyl-L-carnitine in the management of hepatic encephalopathy due to cirrhosis are unclear (58922,58949,59002,90759). A meta-analysis of the available clinical research shows that taking acetyl-L-carnitine 2 grams twice daily for 90 days does not improve quality of life or fatigue in this population when compared with placebo. However, major clinical outcomes, such as all-cause mortality, days of hospitalization, and serious adverse events, have not been evaluated. Additionally, the validity of these findings is limited by the small size, high risk for bias, and heterogeneity of the included studies (100350).
• Hypertension. It is unclear if oral acetyl-L-carnitine lowers blood pressure in adults with hypertension. Details: Clinical research in patients with hypertension, type 2 diabetes, and dyslipidemia shows that taking acetyl-L-carnitine 1 gram twice daily for 6 months does not improve systolic or diastolic blood pressure when compared with placebo. Most patients were already being treated with antihypertensive drugs prior to treatment with acetyl-L-carnitine, in addition to medications for dyslipidemia and diabetes (96937). It is unclear if acetyl-L-carnitine reduces blood pressure in patients with uncontrolled hypertension.
• Infertility. Although there has been interest in using oral acetyl-L-carnitine for infertility in females, there is insufficient reliable information about the clinical effects of acetyl-L-carnitine for this purpose.
• Lyme disease. Although there has been interest in using oral acetyl-L-carnitine for Lyme disease, there is insufficient reliable information about the clinical effects of acetyl-L-carnitine for this purpose.
• Multiple sclerosis-related fatigue. It is unclear if oral acetyl-L-carnitine is beneficial in patients with multiple sclerosis-related fatigue. Details: One small clinical study in patients with multiple sclerosis shows that taking acetyl-L-carnitine 1 gram twice daily for one month reduces fatigue by approximately 25% when compared with placebo (90760).
• Obesity. Although there has been interest in using oral acetyl-L-carnitine for obesity, there is insufficient reliable information about the clinical effects of acetyl-L-carnitine for this purpose.
• Peripheral neuropathy. Although there has been interest in using oral acetyl-L-carnitine for peripheral neuropathy, there is insufficient reliable information about the clinical effects of acetyl-L-carnitine for this purpose.
• Peyronie disease. A small clinical study suggests that oral acetyl-L-carnitine may modestly improve symptoms of Peyronie disease. Details: One small clinical trial in patients with acute and early chronic Peyronie disease shows that taking acetyl-L-carnitine 1 gram twice daily for 3 months reduces pain and slows disease progression when compared with tamoxifen 20 mg twice daily (10076).
• Polycystic ovary syndrome (PCOS). It is unclear if acetyl-L-carnitine is beneficial in patients with PCOS. Details: A clinical study in patients with PCOS shows that taking acetyl-L-carnitine 1.5 grams, in combination with metformin and pioglitazone, twice daily for 12 weeks improves menstrual irregularity and insulin resistance when compared with baseline. The lack of statistical comparison to placebo, as well as the combined use with metformin and pioglitazone, limits the validity of these findings (107396).
• Schizophrenia. It is unclear if oral acetyl-L-carnitine is beneficial in patients with schizophrenia. Details: A very small, open-label clinical study in patients with schizophrenia who partially responded to clozapine therapy shows that taking acetyl-L-carnitine 1 gram daily, in combination with clozapine 300-600 mg daily, for 12 weeks reduces positive symptoms of schizophrenia, but not cognitive function or other clinical symptoms, when compared with baseline (95063). The validity of these findings is limited by the lack of a comparator group.
• Sciatica. It is unclear if oral acetyl-L-carnitine is beneficial in patients with sciatica. Details: One small clinical trial in patients with sciatica secondary to a herniated disc shows that taking acetyl-L-carnitine (Nicetile, SigmaTau Ind. Farm. Riunite SpA,) 1180 mg daily for 60 days decreases the use of analgesics when compared with baseline. However, acetyl-L-carnitine appears to be less effective than alpha-lipoic acid (Byodiniral 300 QR, MDM SpA,) 600 mg daily for reducing lower limb pain and the use of analgesics (21671).
• Stroke. It is unclear if oral acetyl-L-carnitine is beneficial following a stroke. Details: Clinical research in patients with an acute ischemic stroke given routine care shows that oral or nasogastric acetyl-L-carnitine 1 gram three times daily for 3 days modestly improves stroke impairment and overall function 3 months after the stroke when compared with taking placebo. The proportion of patients taking acetyl-L-carnitine with no symptoms or obvious disability at 3 months was 53%, compared with 29% of patients taking placebo. The patients in this study were not candidates of reperfusion therapy and initiated acetyl-L-carnitine within 24 hours of the stroke (111894).
• Toxin-induced liver damage. Oral acetyl-L-carnitine has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: A small clinical study in patients being treated with anti-tuberculosis drugs shows that taking acetyl-L-carnitine 250 mg, along with coenzyme Q10 and alpha-lipoic acid, twice daily for 2 weeks reduces the risk of drug-induced liver injury by 73% when compared with placebo (107445). It is unclear if these findings are due to acetyl-L-carnitine, other ingredients, or the combination. More evidence is needed to rate acetyl-L-carnitine for these uses.

(Read more about ACETYL-L-CARNITINE)

POSSIBLY EFFECTIVE

• Alzheimer disease. Oral alpha-GPC, taken alone or in combination with donepezil, may be beneficial for improving cognitive function in patients with Alzheimer disease. Details: A meta-analysis of 3 moderate-sized clinical studies in patients with Alzheimer disease shows that taking alpha-GPC 1200 mg daily for up to 6 months improves cognitive function as measured using the Mini-Mental State Examination (MMSE) when compared with placebo. Additionally, an analysis of 4 different clinical trials in patients with Alzheimer disease shows that taking alpha-GPC 1200 mg with donepezil 10 mg daily for up to 2 years improves cognitive function as measured using the MMSE and Alzheimer's Disease Assessment Scale - cognition subscale (ADAS-Cog) and may decrease behavioral symptoms and improve functional abilities when compared with donepezil alone (111731).

INSUFFICIENT RELIABLE EVIDENCE to RATE

• Brain tumor. It is unclear if oral alpha-GPC is beneficial in patients with brain tumors. Details: Observational research in patients being treated for glioblastoma suggests that taking alpha-GPC, around 400 mg 2-3 times daily, for 12 months or longer is associated with a 14-month-increase in overall survival but no improvement in progression-free survival when compared with patients not taking alpha-GPC (111732). The validity of these findings is limited by the retrospective nature of the study.
• Cognitive function. Although there has been interest in using oral alpha-GPC to improve cognitive function in healthy adults, there is insufficient reliable information about the clinical effects of alpha-GPC for this purpose.
• Stroke. It is unclear if intramuscular or oral alpha-GPC is beneficial for preventing stroke or improving post-stroke outcomes. Details: A large, open-label, uncontrolled clinical trial in patients who experienced a stroke or transient ischemic attack within the past 10 days shows that intramuscular administration of alpha-GPC 1200 mg daily for 28 days, followed by 400 mg three times daily by mouth for 6 months, modestly improves cognitive and behavioral function when compared to baseline (12102). The validity of this finding is limited by the lack of a comparator group. While this evidence suggests that alpha-GPC may offer some benefit in patients recovering from stroke, observational research in healthy individuals aged 50 years and older has found that alpha-GPC use is associated with a 43% greater risk of stroke, including a 34% greater risk of ischemic stroke and a 37% greater risk of hemorrhagic stroke, when compared with non-users at 10-years' follow-up. Additionally, alpha-GPC use for 2-6 months, 6-12 months, or greater than 12 months is associated with a greater risk of stroke when compared with alpha-GPC use for less than 2 months, suggesting that the increase in stroke risk may be dependent on the total dose received or duration of exposure (108883).
• Vascular dementia. It is unclear if intramuscular alpha-GPC is beneficial in patients with vascular dementia. Details: A small, open-label study in adults with mild to moderate vascular dementia shows that intramuscular administration of a prescription-only formulation of alpha-GPC (Delecit; not available in the US) 1000 mg daily for 90 days improves cognitive function, behavior, mood, and functionality similarly to cytosine diphosphocholine (CDP) 1 gram daily (12101). It is not clear how these improvements compare with standard care. More evidence is needed to rate alpha-GPC for these uses.

(Read more about ALPHA-GPC)

POSSIBLY INEFFECTIVE

• Athletic performance. Taking oral choline before exercise does not improve athletic performance. Details: Clinical research in trained athletes shows that taking oral choline 2.43 grams as a single dose does not delay fatigue during endurance sports when compared with placebo (5164). Other clinical research in untrained adults shows that taking oral choline 8.425 grams or 50 mg/kg once prior to participating in exhaustive, load-carrying exercise does not improve dexterity, upper or lower body strength, grip strength, or run time-to-exhaustion following exercise when compared with placebo (42229,42237).

INSUFFICIENT RELIABLE EVIDENCE to RATE

• Age-related cognitive decline. It is unclear if oral choline is beneficial in patients with age-related cognitive decline. Details: Small clinical studies in adults with memory loss shows that taking choline 2 grams four times daily orally for 21 days does not improve memory when compared with placebo (5170). Observational research in adults over 60 years of age has found that intake of choline 187-399.5 mg daily is associated with a 33% to 42% reduced odds of low cognitive function when compared with intake of less than 187 mg daily. Intake of more than 399.5 mg daily was not associated with low cognitive function when compared with less than 187 mg daily (109100).
• Allergic rhinitis (hay fever). It is unclear if oral choline is beneficial in patients with allergic rhinitis. Details: Preliminary clinical research shows that taking oral choline, as tricholine citrate, 500 mg three times daily for 8 weeks is less effective than intranasal budesonide 200 mcg twice daily for reducing symptoms of allergic rhinitis (42252).
• Alzheimer disease. Although there has been interest in using oral choline for Alzheimer disease, there is insufficient reliable information about the clinical effects of choline for this purpose.
• Asthma. Small clinical studies suggest that oral choline may modestly improve symptoms in patients with asthma. Details: Preliminary clinical research shows that taking choline 500-1000 mg orally three times daily for 3-4 months decreases the severity of symptoms, the number of symptomatic days, and the need to use bronchodilators in patients with asthma when compared with placebo (5165,5166). Preliminary data also shows that choline 3 grams daily might be more effective than 1.5 grams daily (5165).
• Autism spectrum disorder. Oral choline has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: Clinical research shows that taking a combination of donepezil 2.5-5 mg daily and choline bitartrate 350 mg daily for 12 weeks improves receptive language skills, but no other outcomes, for up to 6 months after treatment when compared with placebo in children aged 5-10 years with autism spectrum disorder. Also, adolescents aged 11-16 years experienced no benefits, and some experienced an increase in behavioral symptoms, such as irritability (103571). It is unclear if this effect is due to choline, donepezil, or the combination.
• Breast Cancer. It is unclear if dietary intake of choline reduces the risk of breast cancer. Details: A meta-analysis of 6 low to moderate-quality observational studies suggests that neither high nor low dietary intake of choline is associated with breast cancer risk. This finding is largely influenced by inclusion of the European Prospective Investigation into Cancer and nutrition (EPIC) cohort study, which analyzed data from over 300,000 subjects. However, subanalysis of 3 case-control studies suggests that high dietary intake of choline may be associated with a decreased risk of breast cancer when compared with low choline intake (111416). The interpretation of these findings is limited by the heterogeneity of the included studies, self-reported data, and a small number of studies.
• Bronchitis. Although there has been interest in using oral and inhaled choline for bronchitis, there is insufficient reliable information about the clinical effects of choline for this purpose.
• Cancer. It is unclear if dietary choline intake reduces the risk for cancer. Details: A meta-analysis of 11 low-quality population studies has found that high dietary intake of choline is associated with an 18% lower risk of cancer when compared with low choline intake. High dietary intake of both choline and betaine was associated with a 40% lower risk of cancer (97390).
• Cardiovascular disease (CVD). It is unclear if dietary choline intake reduces the risk of CVD or improves outcomes in patients with CVD. Details: A meta-analysis of population research has found that high intake of dietary choline is not associated with a lower risk of coronary artery disease, stroke, or mortality when compared with a diet low in choline (97388). A more recent population study has found that energy-adjusted total choline intake is not associated with the incidence of CVD over ten years. However, the highest intake of free choline is associated with a 34% reduced risk of CVD when compared with the lowest intake (109104).
• Cerebellar ataxia. It is unclear if oral choline is beneficial in patients with cerebellar ataxia. Details: Despite some anecdotal reports suggesting that taking choline improves motor function, preliminary clinical research shows that taking choline 4-5 grams orally daily for 4 days to 6 weeks does not reduce cerebellar ataxia (5161,5173,23679).
• Cognitive function. It is unclear if oral choline is beneficial for improving cognitive function in healthy adults. Details: Preliminary clinical research shows that taking a single dose of choline 50 mg/kg orally prior to participating in an exhaustive, load-carrying task does not improve reaction time, reasoning, memory, or serial addition and subtraction ability following the task when compared with placebo (42237). Also, preliminary clinical research in patients requiring long-term total parenteral nutrition (TPN) shows that adding choline chloride 2 grams daily to TPN for 24 weeks might improve delayed visual memory, but does not improve other measures of cognitive performance, when compared with TPN alone (42232).
• Cirrhosis. Although there has been interest in using oral choline for cirrhosis, there is insufficient reliable information about the clinical effects of choline for this purpose.
• Complex partial seizures. Although there has been interest in using oral choline for complex partial seizures, there is insufficient reliable information about the clinical effects of choline for this purpose.
• Dementia. Although there has been interest in using oral choline for dementia, there is insufficient reliable information about the clinical effects of choline for this purpose.
• Depression. It is unclear if oral choline is beneficial for the treatment or prevention of depression. Details: Observational research has found that dietary choline intake of at least 198 mg daily is associated with a 32% to 43% decreased risk of depressive symptoms when compared with intakes of less than 198 mg daily (109106). It is unclear if choline supplementation is beneficial for depression.
• Diabetes. It is unclear if oral choline is beneficial for the treatment or prevention of type 2 diabetes; the available research is conflicting. Details: Preliminary clinical research shows that taking oral choline bitartrate 1000 mg daily for 2 months does not affect coagulation parameters or levels of triglycerides, low-density lipoprotein (LDL) cholesterol, or high-density lipoprotein (HDL) cholesterol in patients with type 2 diabetes (103569). Choline has also been evaluated for the prevention of type 2 diabetes. In Finnish males, observational research has found that dietary intake of total choline at levels of more than 482 mg daily, especially as phosphatidylcholine, is associated with a 25% lower risk of developing type 2 diabetes over the following 19.3 years when compared with intakes of less than 382 mg daily (103567). However, in males and females in the US, additional observational research has found no association between dietary choline and risk of type 2 diabetes over a mean of 9 years (103570). In addition, a sub-analysis found that the highest intakes of choline (a median of 487 mg daily) were associated with a 54% higher risk of type 2 diabetes among females, but not males, when compared with the lowest intakes (a median of 175 mg daily) (103570). Population research in patients with diabetes has found that an intake of dietary choline in amounts of at least 279 mg daily is associated with a 2.1-fold increased odds of diabetic retinopathy in females, but not males, when compared with an intake less than 206 mg daily (109102). It is unclear if choline itself is responsible for the increased odds of diabetic retinopathy in this population.
• Fetal alcohol spectrum disorders (FASD). It is unclear if oral choline improves cognition in children with fetal alcohol spectrum disorders (FASD). Details: Clinical research in children aged 2.5-5 years with FASD shows that taking oral choline bitartrate, providing choline 500 mg, daily for 9 months does not improve global cognitive development or hippocampal-dependent memory when compared with placebo. However, a subgroup analysis of only children aged 2.5-4 years suggests that choline may improve hippocampal-dependent memory (92112). Follow-up of this study at 7 years shows that choline improves motor speed and suggests a trend towards improved color naming, which are components of executive functioning testing, when compared with placebo (111745). The validity of these findings is limited by the high rate of patient discontinuation which limits statistical power. A small clinical trial in children 5-10 years old with FASD shows that taking oral glycerophosphocholine, providing choline 625 mg, daily for 6 weeks does not improve cognitive function, executive function, attention, or hyperactivity when compared with placebo (97389).
• Hepatitis. Although there has been interest in using oral choline for hepatitis, there is insufficient reliable information about the clinical effects of choline for this purpose.
• Huntington disease. Although there has been interest in using oral choline for Huntington disease, there is insufficient reliable information about the clinical effects of choline for this purpose.
• Hypertension. It is unclear if oral choline is beneficial for the prevention or treatment of hypertension. Details: Population research has found that every 100-mg increase in daily dietary choline intake is associated with a 15% decreased risk of developing hypertension over the next 4.6 to 9.1 years (109098). However, it is unclear if any benefits are specifically related to dietary choline or whether choline supplementation is beneficial.
• Infant development. It is unclear if oral choline intake during pregnancy is beneficial for infant development; the available research is conflicting. Details: Two observational studies have found that higher intake of choline during the second and third trimesters of pregnancy is associated with improvement in offspring cognitive development and visual memory at the age of 18 months and 7 years, respectively, when compared with lower choline intake (94654,94657). One of these studies found that each 1 mcmol/L increase in maternal blood levels of choline at 16 weeks' gestation was associated with a 2.23-point increase in cognitive skill score based on the Bayley Scales of Infant Development (BSID-III) at 18 months of age (94657). Also, some observational research has found that higher plasma levels of choline during pregnancy are associated with higher processing speed and decreased social withdrawal at 4 years of age in the offspring (109101). In contrast, 3 observational studies have found that higher intake of choline during pregnancy, as well as higher maternal and cord blood levels of choline, are not associated with improved offspring intelligence at 5 years of age or cognitive performance at 3 or 7 years of age (94654,94655,94656). However, many of these observational studies, including those with positive findings, included populations with a mean intake of choline that was below the recommended adequate intake of 450 mg daily (94654,94656). It's possible that higher intake of choline is needed to observe a benefit; however, research on the effects of choline supplementation is limited. One small clinical trial shows that taking choline 930 mg daily during the third trimester modestly improves sustained attention in the child at 7 years of age when compared with taking 480 mg daily (109105).
• Metabolic syndrome. It is unclear if oral choline is beneficial in patients with metabolic syndrome. Details: Preliminary clinical research in adults with metabolic syndrome shows that taking oral choline 400 mg daily for 4 weeks does not decrease body weight, blood pressure, plasma glucose levels, or low-density lipoprotein (LDL) cholesterol levels, or increase high-density lipoprotein (HDL) cholesterol levels, when compared with baseline (105731).
• Neural tube birth defects. It is unclear if oral choline intake is beneficial for preventing neural tube defects. Details: Population research has found that females who have a high dietary choline intake around the time of conception have a lower risk of having offspring with a neural tube defect when compared to those with lower intake (13134).
• Nonalcoholic fatty liver disease (NAFLD). It is unclear if oral choline is beneficial in patients with nonalcoholic fatty liver disease (NAFLD). Details: A cross-sectional analysis of results from observational and clinical research shows that low dietary intake of choline is associated with increased fibrosis in postmenopausal adults with NAFLD, but not in children, males, or premenopausal adults with NAFLD. Dietary choline intake was not associated with steatosis severity in any patient subgroup (92109).
• Schizophrenia. Although there has been interest in using oral choline for schizophrenia, there is insufficient reliable information about the clinical effects of choline for this purpose.
• Tourette syndrome. Although there has been interest in using oral choline for Tourette syndrome, there is insufficient reliable information about the clinical effects of choline for this purpose.
• TPN-associated hepatic steatosis. It is unclear if intravenous choline is beneficial in patients with TPN-associated hepatic steatosis. Details: In patients receiving long-term total parenteral nutrition (TPN), plasma levels of choline can decrease. Small, low-quality clinical studies show that administering intravenous choline 1-4 grams daily for 24 weeks improves some markers of TPN-associated hepatic steatosis when compared with baseline or placebo (5174,42235). More evidence is needed to rate choline for these uses.

(Read more about CHOLINE)

EFFECTIVE

• Folate deficiency. Oral or intravenous folic acid is effective for the prevention or treatment of folate deficiency. Details: Administering folic acid orally or parenterally improves and prevents folate deficiency (505,8739). Clinical research shows that supplementation with folic acid 100 mcg to 5 mg daily during pregnancy decreases the risk of developing megaloblastic anemia by up to 79% (91307).

LIKELY EFFECTIVE

• Kidney failure. Taking folic acid orally reduces homocysteine levels in people with kidney failure who are on hemodialysis. Details: Over 85% of people with kidney failure have hyperhomocysteinemia. Treatment of hyperhomocysteinemia in kidney failure is often more difficult than with normal kidney function (1489,3324,7289,9413,9414,9416). The reasons for this are not fully understood; renal uptake and metabolism of homocysteine may be reduced in severe kidney failure, and hemodialysis may contribute to vitamin deficiencies (6884,9414,9417). Folic acid 0.8-15 mg daily or 3 times weekly is generally used, but the degree of homocysteine reduction varies between 12% to 50%, and normal homocysteine levels (less than 12 µmol/L) cannot always be achieved. Adding vitamin B12 400-1000 mcg daily and vitamin B6 20-50 mg daily produces an additional reduction in homocysteine (1489,6884,7289,7881,9322,9413,9414,9415,9416,9417). Folic acid doses greater than 15 mg daily do not seem to provide additional benefit. Also, doses of 30-60 mg might cause a rebound in homocysteine levels when treatment is stopped (9219). Despite the homocysteine-lowering effect of folic acid in kidney failure, the most robust meta-analysis of 11 clinical trials suggests that folic acid supplementation does not seem to reduce the risk of cardiovascular events (50527). A smaller meta-analysis of 7 clinical trials that used a different primary composite outcome suggests that folic acid might reduce the risk of cardiovascular events by 15% when compared with control (91311). There has also been interest in using a reduced form of folic acid, L-5-methyltetrahydrofolate (L-5-MTHF). One study in patients on hemodialysis suggests that taking L-5-MTHF 17 mg daily for 12 weeks might lower homocysteine levels to a greater extent than an equimolar 15 mg of folic acid (104908). Another clinical trial in patients on hemodialysis suggests that giving intravenous L-5-MTHF 50 mg three times weekly is associated with an increased survival of about 36 months, compared with about 26 months with folic acid 5 mg daily. There was no difference in homocysteine reduction between groups (104909). These results should be interpreted with caution because they have not been replicated, and there was no placebo control. Furthermore, survival may have been affected by the availability of kidney transplants.
• Hyperhomocysteinemia. Oral folic acid, taken alone or in combination with other B vitamins, lowers homocysteine levels in most patients. However, it is unclear if this has cardiovascular benefits. Details: Taking folic acid orally 0.4-5 mg daily lowers fasting homocysteine levels by 20% to 30% in people with normal to moderately elevated homocysteine levels at baseline. Folic acid 0.8-1 mg daily seems to provide maximal reduction (9307,9400,9401,9405,9408,11337,11338,50145). Doses above 1 mg daily do not seem to add benefit (9307), except in some people with certain gene mutations that cause homocysteine levels of 20 µmol/L or higher (9408). The higher the initial homocysteine levels, the lower the folic acid dose needed to attain maximum homocysteine reduction (9307). The effects of folic acid supplementation on homocysteine concentrations appear to be greater in females than males (50145). Adding vitamin B6 25-250 mg or vitamin B12 500 mcg seems to further reduce homocysteine levels (1489,9400,9405,9406,9408,107136). Some experts recommend routine use of vitamin B12 in homocysteine-lowering regimens to avoid the risk of neuropathy in people with undetected vitamin B12 deficiency (9405). Increasing folic acid intake with supplements or folate-fortified cereal products is more effective for reducing homocysteine levels than increasing intake of folate-rich foods (6367). Fortification of cereals and flour with 140 mcg folic acid per 100 grams reduces the mean homocysteine level in the general population by about 7% (7881,9404,9407). Elevated homocysteine levels are considered by some to be an independent risk factor for atherosclerosis progression, recurrent thromboembolism, deep vein thrombosis, myocardial infarction, ischemic stroke, and other vascular complications (3886,3887,6236,7725,9314,9318,50509). However, elevated homocysteine levels may be a marker, as opposed to a cause, of vascular disease (11387,11388). Although folic acid lowers homocysteine levels, it is not yet known whether this reduces the risk of vascular disease. One meta-analysis shows that taking folic acid can reduce the risk of stroke by about 10% in patients with cardiovascular disease (CVD); the reduction is greatest in patients for whom homocysteine levels are lowered by at least 25% (96157). A meta-analysis of 10 clinical trials, including over 44,000 patients at risk for or with a history of CVD, shows that B vitamin supplementation reduces the relative risk of stroke by 10% when compared with placebo (97619). Also, a meta-analysis in patients with a history of stroke shows that B vitamin supplementation, including folic acid, reduces the relative risk of stroke recurrence by 13% and the risk of vascular death by 11% when compared with placebo (107136). However other research does not agree. Meta-analyses of clinical research show that folic acid does not prevent CVD or coronary heart disease, in spite of lowering homocysteine by up to 55%, when individuals with normal or high levels of homocysteine are considered (50539,96147,97619). Furthermore, most research shows that folic acid supplementation, alone or in combination with vitamin B6 and vitamin B12, does not improve endothelial function or improve secondary prevention of cardiovascular events such as myocardial infarction in people with existing CVD despite a homocysteine-lowering effect (9313,11337,11387,13482,50437,97619). Some research even suggests an increase in CVD risk concurrent with homocysteine lowering (13482). Large randomized controlled trials are needed to confirm or refute these findings. Some researchers hypothesize that different genetic profiles might explain some of these conflicting results. For instance, individuals with a homozygous 677TT MTHFR genotype typically have increased homocysteine levels. However, a meta-analysis suggests that treatment with folic acid does not reduce the risk of ischemic heart disease despite reducing homocysteine levels in individuals with 677TT MTHFR (50456). It has also been theorized that a reduced form of folic acid, 5-methyltetrahydrofolate (5-MTHF) might work better in these individuals. Although [6RS]-5-MTHF has been shown to lower homocysteine levels (104915), studies assessing its cardiovascular benefits are lacking.
• Methotrexate toxicity. Oral folic acid reduces the severity of methotrexate toxicity. Details: Oral folic acid reduces methotrexate toxicity symptoms, such as nausea and vomiting, in the treatment of rheumatoid arthritis (RA) and psoriasis (768,2162,2163,2164,4492,4493,4494,9369,9419). Folic acid also seems to reduce methotrexate-induced hepatic side effects by approximately 36% (50320). Some research shows that a low, 0.8 mg weekly dose of folic acid is equally effective to a higher dose of 5 mg weekly for the prevention of methotrexate toxicity (102388).
• Neural tube birth defects. Oral folic acid helps to prevent neural tube birth defects in newborns. Details: Clinical practice guidelines recommend that anyone capable of becoming pregnant take folic acid 400 mcg daily from fortified foods or supplements to prevent neural tube birth defects in infants. Folic acid 600 mcg daily is advised during pregnancy (94811,96146). This recommendation is based on research showing that a higher intake of folic acid from food and supplements during pregnancy reduces the primary incidence of neural tube birth defects by 41% to 69% (3325,9309,50344,50403,50468,95156). Individuals with a history of children with neural tube birth defects usually take a higher dose of folic acid 4000 mcg daily starting one month before and continuing for up to 3 months after conception (96146). Evidence shows that, when used for secondary prevention, folic acid supplementation reduces the incidence of neural tube defects by 66% to 87% (21235,50263,50344,50403,95156). In the US, foods containing at least 60 mcg of folic acid can be labeled with a health claim stating that healthful diets with adequate folic acid intake may reduce the risk of having a child with a brain or spinal cord defect (102369).

POSSIBLY EFFECTIVE

• Cognitive impairment. Taking folic acid alone, with other B vitamins or with docosahexaenoic acid (DHA), might improve thinking and memory skills in older patients with cognitive impairment. Details: One clinical trial in patients aged 65 years and older with mild cognitive impairment (MCI) shows that taking folic acid 400 mcg daily for 2 years increases IQ scores when compared with placebo (100952). Two small, low-quality clinical studies in patients aged 70-90 years with cognitive impairment and low folate levels or folate deficiency shows that taking folic acid 5 or 15 mg daily for up to 63 days improves cognitive function, including measures such as memory and attention, when compared with placebo or baseline (50301,104911). Folic acid also appears to be beneficial when used in combination with other B vitamins or with DHA. A clinical trial in patients aged 70 years and older with MCI shows that taking folic acid 800 mcg, vitamin B6 20 mg, and vitamin B12 500 mcg daily for 2 years mitigates decline in executive function and, in patients with high baseline homocysteine levels, improves cognition and memory when compared with placebo (50480). Taking folic acid 800 mcg with or without DHA 800 mg daily for 6 months modestly improves cognition, as measured on the full-scale intelligence quotient, when compared with placebo (103978,109196). However, this benefit is no longer present at 6 months after treatment discontinuation (109196).
• Depression. Oral folic acid seems to modestly reduce depression severity when added to conventional antidepressant therapy. It is unclear if folic acid can reduce the prevalence of depression or the risk for suicide. Details: Observational studies suggest that depression is correlated with low folate status, particularly in females (50105,50127,50243). Taking folic acid 0.2-15 mg daily for up to 6 months with conventional antidepressants seems to improve treatment response in patients with major depressive disorder (3657,10884,10887,50566,109190). One meta-analysis shows that taking L-methylfolate or folic acid as an adjunct to treatment with conventional antidepressants modestly reduces depression severity when compared with placebo and conventional antidepressants. The response and remission rates were improved by 36% and 39%, respectively (109190). However, limited clinical research suggests that folic acid is not effective as a replacement for conventional antidepressant therapy (10886). Also, a small clinical study in adolescents at high familial risk for mood disorders suggests that taking folic acid 2.5 mg daily for up to 36 months does not prevent mood disorders when compared with placebo. However, in the patients that were eventually diagnosed with depression, the time of onset was delayed from 5 months to 15.5 months in the group using folic acid when compared with placebo (91313). Guidelines from The World Federation of Societies of Biological Psychiatry (WFSBP) and Canadian Network for Mood and Anxiety Treatments (CANMAT) Taskforce state that folic acid is not currently recommended as monotherapy treatment for unipolar depression (110318). Observational research has also evaluated the association between folic acid supplementation and suicidal events in patients with or without depression. One within-person cohort study, in which only 12% of patients were diagnosed with depression, has found that filling a folic acid prescription of 0.4-5 mg daily, either alone or as part of a multivitamin, is associated with a reduced risk for suicidal events during the following months when compared with months without a prescription (109201). It is unclear what percentage of these patients, if any, had folate deficiency at baseline.
• Hypertension. Oral folic acid seems to modestly reduce hypertension. Details: A meta-analysis of clinical research shows that taking folic acid 5-10 mg daily for at least 6 weeks reduces systolic blood pressure by 2mmHg and improves flow-mediated dilation by 1.6% in hypertensive individuals (50364). Some research has evaluated folic acid in hypertensive patients when used with antihypertensive drugs. Results show that taking folic acid 400-800 mcg in combination with enalapril 10 mg daily for about 4.5 years does not improve blood pressure when compared with enalapril alone (50302,96158). However, in hypertensive patients with heavy proteinuria, this combination seems to reduce the risk of all-cause mortality by about 41% when compared with enalapril alone (96158).
• Phenytoin-induced gingival hyperplasia. Topical folic acid seems to reduce gingival hyperplasia due to phenytoin. The effect of oral folic acid is unclear. Details: Applying folic acid topically seems to inhibit gingival hyperplasia secondary to phenytoin therapy (2151). However, taking folic acid orally does not seem to improve gingival hyperplasia secondary to phenytoin therapy in adults (2150,2151,2152), although some evidence suggests that taking folic acid 500 mcg daily reduces the risk of phenytoin-induced gingival hyperplasia by 33% in children when compared with placebo (50463).
• Stroke. Although some clinical research has shown that oral folate reduces stroke risk by a small amount, more research is needed to determine who is most likely to benefit. Most individual clinical trials show that folic acid seems to reduce stroke risk only in regions without food-fortification policies. Details: Multiple clinical studies have shown that folic acid supplementation reduces the risk of stroke by 10% to 25% in regions WITHOUT established policies mandating folic acid fortification of grain products (50240,50485,50525,50539,91325,96154,96157,96159,97308). The effect appears to be greatest when folic acid is taken in low doses (usually 0.8 mg daily or lower) (50525,96157,96159), in regions with a low prevalence of statin use (50525,96159), in patients with high cholesterol levels at baseline (96152), in patients who achieve homocysteine reduction of at least 20% (50407,96157), and in patients with the lowest folate levels at baseline (96154,96157). There is also some evidence that the effect of folic acid on stroke risk is greatest in patients with low baseline levels of vitamin B12 (96159). In 2001, the US Food and Drug Administration (FDA) allowed a qualified health claim stating that, as part of a well-balanced diet that is low in saturated fat and cholesterol, folic acid, vitamin B6, and vitamin B12 may reduce the risk of vascular disease (102368). Most research shows that folic acid supplementation does not reduce the risk of stroke in regions WITH established policies mandating folic acid fortification (50240,50485,50525,50539,96157,96159,97308). However, there is some evidence that folic acid may reduce the risk of stroke in patients from regions with folic acid fortification who have recently had a stroke or transient ischemic attack and are not using antiplatelet drugs (90379). Meta-analyses of clinical research have been conducted. However, possible confounding due to the presence or absence of folic acid fortification is unclear. A meta-analysis of the available research in adults with existing CVD shows that folic acid supplementation at a daily dose of less than 2 mg reduces the risk for stroke by about 10% (102386). Also, a meta-analysis of 10 clinical trials, including over 44,000 patients at risk for or with a history of CVD, shows that B vitamin supplementation, including folic acid, reduces the relative risk of stroke by 10% when compared with placebo (97619). In patients with a history of stroke, a meta-analysis shows that B vitamin supplementation reduces the relative risk of stroke recurrence by 13% and the risk of vascular death by 11% when compared with placebo (107136). It is unclear if folic acid reduces the stroke risk in patients with impaired kidney function. Some research shows that taking folic acid in combination with high doses of vitamin B12 (cyanocobalamin) does not reduce the risk of stroke in these patients (11387,96150). However, there is concern that the lack of benefit may have been due to the decline in kidney function from high doses of cyanocobalamin (96150). Additional research is needed to determine if folic acid supplementation is beneficial in patients with impaired kidney function when used with other forms of vitamin B12 such as methylcobalamin or hydroxycobalamin.
• Vitiligo. Oral folic acid seems to improve vitiligo symptoms. Details: Taking folic acid orally seems to improve symptoms of vitiligo (2153,2154). This finding is supported by a meta-analysis of observational research which shows that patients with vitiligo have higher serum homocysteine levels when compared with patients without vitiligo (100951).

POSSIBLY INEFFECTIVE

• Anemia. Adding oral folic acid to oral iron therapy does not seem to improve hematologic parameters in patients with anemia. Details: In postpartum patients with anemia, clinical research shows that taking iron as ferrous fumarate 600 mg and folic acid 1 mg daily is no more effective than iron alone for improving hemoglobin status (91319). Also, clinical research in non-pregnant menstruating females shows that taking folic acid 0.4 mg daily or 2.8 mg once weekly for 16 weeks with iron 60 mg daily does not reduce anemia or improve iron status when compared with iron alone (109193). During pregnancy, clinical research shows that folic acid supplementation does not decrease the risk of pre-delivery anemia or low hemoglobin levels (91307).
• Age-related cognitive decline. Oral folic acid does not seem to prevent cognitive decline in healthy elderly adults. Details: Most clinical research shows that taking folic acid, alone or in combination with other B vitamins, does not improve cognitive function, including memory, language, or executive function, in elderly adults with age-related cognitive decline (50318,50412,50510). In fact, a large-scale observational study in the US has found that people over 65 years of age who consume large amounts of folic acid (median of 742 mcg daily) have cognitive decline at a rate twice as fast as those consuming smaller amounts (median of 186 mcg daily) (13068). While most research on folic acid for age-related cognitive decline lacks positive findings, many of the studies are small, short-term (<1 year), underpowered to detect significant differences, and not specific to patients with high homocysteine levels. Population research has found that high homocysteine levels are associated with decreased cognition in older adults, suggesting that using folic acid to lower homocysteine levels might mitigate cognitive decline in these patients (50094). Two long-term clinical trials examining the effects of folic acid in elderly adults with high homocysteine levels show mixed results. A large-scale clinical trial of patients aged 50-70 years from the Netherlands who have high homocysteine levels shows that taking folic acid 800 mcg daily for 3 years increases memory, information processing, and other measures of cognitive function when compared with placebo (15271). However, another large-scale clinical trial of patients aged 65 years and older from the Netherlands who have high homocysteine levels shows that taking folic acid 400 mcg and vitamin B12 500 mcg daily for 2 years lowers homocysteine levels, but does not appear to improve overall measures of cognitive function, when compared with placebo (90392). The reasons for the discrepant findings in these two studies are not clear but might relate to differences in the dose of folic acid, duration of treatment, and age of patients included.
• Cataracts. Oral folic acid does not seem to reduce cataract development. Details: Clinical research in females with existing cardiovascular disease (CVD) or with risk factors for CVD shows that taking folic acid 2.5 mg, vitamin B6 50 mg, and vitamin B12 1 mg daily for an average of 7.3 years does not reduce the risk of developing cataracts. Furthermore, the risk of cataract extraction was increased by 28% in these patients (96149).
• Diarrhea. Oral folic acid does not seem to reduce the risk of diarrhea, and might even increase the incidence of diarrhea in children. Details: In children aged 6-30 months at risk of malnourishment, clinical research shows that taking a nutritional supplement (Nutriset Ltd) enriched in folic acid 75-150 mcg, with or without vitamin B12 0.9-1.8 mcg, daily for 6 months does not reduce the incidence of diarrhea when compared with placebo. Enrichment with folic acid, with or without vitamin B12, actually seems to increase the likelihood of having more episodes of both persistent diarrhea and diarrhea lasting over 3 days (90391).
• Fall prevention. Oral folic acid does not seem to reduce the risk of falls. Details: Clinical research shows that taking a combination of B vitamins, including folic acid 400 mcg and vitamin B12 500 mcg daily, for 2 years, does not prevent falls when compared with placebo in elderly individuals also taking vitamin D (96148).
• Fetal and premature infant mortality. Oral vitamin B12 does not seem prevent mortality in premature infants. Details: Clinical research shows that supplementation with folic acid during pregnancy does not decrease the risk of miscarriage, stillbirth, or neonatal death (91307,96156).
• Leukemia. Oral vitamin B12 does not seem to reduce the risk for pediatric acute lymphoblastic leukemia. Details: A meta-analysis of results from two case-control studies has found that increased folate intake during pregnancy is not associated with a reduced risk of childhood acute lymphoblastic leukemia (50247).
• Male infertility. Oral folic acid does not seem to improve sperm parameters or pregnancy rates in males with infertility. Details: Some small clinical studies show that taking folic acid, alone or with zinc, increases sperm count in males with idiopathic infertility or in males with a grade III varicocele (9334,90194). However, another small study in males with asthenozoospermia shows that taking folic acid 5 mg, selenium 200 mcg, and vitamin E 400 IU daily for 3 months does not improve sperm parameters when compared with placebo (104907). Furthermore, there seems to be no improvement in clinical outcomes. One large, high-quality clinical study in males with idiopathic infertility shows that taking folic acid 5 mg with zinc 30 mg daily for 6 months does not improve sperm morphology, pregnancy rate, or live birth rate when compared with placebo (102085). Folic acid has also been evaluated in combination with other ingredients. A retrospective study in males with or without varicocele-related infertility suggests that taking a specific combination product containing folic acid 0.2 mg, vitamin C, zinc, L-carnitine fumarate, acetyl-L-carnitine, coenzyme Q10, selenium, and vitamin B12 (Proxeed Plus, Sigma-Tau) twice daily for 6 months is associated with improvements in sperm count, sperm concentration, and sperm motility when compared to baseline. Improvement in semen parameters were greatest in subjects with more severe varicoceles (111296). The validity of this study is limited by the lack of a comparator group.
• Osteoporosis. Oral folic acid does not seem to reduce the risk of osteoporotic fractures. Details: Clinical research in elderly adults or adults with a history of cerebrovascular disease shows that taking vitamin B12 500 mcg and folic acid 0.4-2 mg, with or without vitamin B6 25 mg, daily for 2-3 years does not seem to reduce the risk for osteoporotic fractures when compared with placebo (90377,90393). A 5-7 year follow-up of this research has also found no benefit (103981).
• Physical performance. Oral folic acid does not seem to improve physical performance in older adults. Details: Clinical research shows that taking a combination of B vitamins, including folic acid 400 mcg and vitamin B12 500 mcg daily for 2 years, does not improve hand strength or improve performance such as walking when compared with placebo in elderly individuals also taking vitamin D (96148).
• Pre-eclampsia. Oral folic acid does not seem to prevent pre-eclampsia in pregnant patients. Details: While the effect of low-dose prenatal folic acid is unclear, high-dose folic acid does not seem to reduce the risk of pre-eclampsia. Some population research has found that low-dose folic acid is associated with a 22% reduced odds of pre-eclampsia, while other research has found no association (91308,99370,99372,110447). A large clinical trial evaluating high-dose folic acid in pregnancies at risk for pre-eclampsia shows that taking 4 mg daily, starting at 8-16 weeks of gestation and continuing until delivery, does not reduce the risk of pre-eclampsia when compared with placebo (103929). A secondary analysis of this study in twin pregnancies has also found no benefit with high-dose folic acid supplementation (103977).
• Respiratory tract infections. Oral folic acid does not seem to prevent respiratory tract infections. Details: Clinical research in children aged 6-30 months at risk of malnourishment shows that taking a nutritional supplement (Nutriset Ltd) enriched in folic acid 75-150 mcg, with or without vitamin B12 0.9-1.8 mcg, daily for 6 months does not reduce the incidence of lower respiratory infections when compared with a supplement not enriched with folic acid and vitamin B12 (90391).

LIKELY INEFFECTIVE

• Colorectal adenoma. Oral folic acid does not prevent colorectal adenomas. Details: Although some population research and one clinical study has found that high folate intake is associated with reduced colorectal adenoma risk (2142,2143,91303), most clinical research does not support this finding. Clinical research shows that taking a combination of B vitamins, including folic acid 2.5 mg, vitamin B6 50 mg, and vitamin B12 1 mg daily for up to 9.2 years, does not reduce the risk of colorectal adenoma in females at high risk of cardiovascular disease when compared with placebo (90389). Other clinical research suggests that taking folic acid does not reduce the occurrence or recurrence of adenomas or incidence of advanced adenomas (34596,50241,50265,50369,50394,50449,50522). Furthermore, treatment with folic acid for more than 3 years seems to be associated with an increased risk of advanced adenomatous lesions (50378).
• Fragile X syndrome. Oral folic acid does not improve symptoms in children with fragile X syndrome. Details: Clinical research shows that taking folic acid orally does not improve symptoms of fragile X syndrome (2155,2156,2157,2158,2159,2160,50575).
• Preterm labor. Oral folic acid does not seem to reduce the risk of preterm birth. Details: Meta-analyses of clinical research show that supplementation with folic acid 200 mcg to 5 mg during pregnancy does not decrease the risk of preterm birth (91307,96155). An observational study in patients with and without epilepsy found that folic acid supplementation during pregnancy was associated with a lower odds of preterm birth in patients receiving antiseizure medications; however, no link between folic acid and preterm labor was reported in patients without epilepsy or in those with epilepsy not receiving antiseizure medications (110447).

INSUFFICIENT RELIABLE EVIDENCE to RATE

• Abdominal wall defects. It is unclear if oral folic acid helps to prevent abdominal wall defects in newborns. Details: Observational research in a population in northern China has found that taking folic acid supplements until the end of the first trimester modestly reduces the risk of abdominal wall defects and the risk of omphalocele, specifically, in the newborn when compared with not taking folic acid. However, this association was not found in a population in southern China (109191). These differing outcomes may be related to the lower dietary folate intakes in northern China.
• Acne. Oral folic acid has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: Preliminary clinical research in adults and children with inflammatory acne shows that taking 1-4 tablets of a specific product (NicAzel, Elorac Inc.) containing folic acid, vitamin B6, nicotinamide, azelaic acid, zinc, and copper for 8 weeks reduces inflammatory lesions and improves appearance in 88% and 81% of patients, respectively, when compared with baseline (90800).
• Age-related macular degeneration (AMD). Oral folic acid has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: A large-scale clinical study shows that taking folic acid 2.5 mg, vitamin B6 50 mg, and vitamin B12 1 mg daily reduces the risk of developing AMD in females over 40 years of age with a history of cardiovascular disease (CVD) or with risk factors for CVD. Those who took this combination for an average of 7.3 years had a 34% reduced risk of developing AMD and a 41% reduced risk of visually significant AMD when compared with placebo (14620). It is unclear if this effect is due to folic acid, other ingredients, or the combination.
• Age-related testosterone deficiency. Folic acid has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: A very small clinical study in males with overweight or obesity, mild erectile dysfunction, and normal to low androgen levels shows that taking a combination product containing folic acid 400 mcg, alpha-lipoic acid, myo-inositol, and apple (Sinopol Forte) increases testosterone, luteinizing hormone, and measures of erectile dysfunction but not follicle-stimulating hormone or sperm parameters when compared to baseline (111674). The validity of these effects is limited by the small sample size and the lack of a comparator group, and it is unclear if these effects are due to folic acid, other ingredients, or the combination.
• Alzheimer disease. It is unclear if oral folic acid reduces the risk of developing this condition. Details: Low levels of folate and high levels of homocysteine have been linked to a greater risk of Alzheimer disease (50094). Also, some observational studies have found that higher intake of folate from the diet and supplements in elderly adults is associated with a reduced risk of developing Alzheimer disease when compared with lower intake (13165,15270). One small clinical trial in patients with Alzheimer disease who are taking cholinesterase inhibitors shows that taking folic acid 1 mg daily for 6 months increases the likelihood of treatment response, classified as global improvement in behavioral and/or functional status with no decline in mental status scores, by 78% to 87% when compared with placebo (50246). Also, preliminary clinical research in patients with probable Alzheimer disease who are not consuming a folate-fortified diet shows that taking vitamin B12 50 mcg daily plus folic acid 1.2 mg daily for 6 months modestly improves some measures of cognitive performance and decreases levels of homocysteine when compared with placebo (107150). However, not all research agrees. Clinical research in patients with probable Alzheimer disease using routine medications shows that taking folic acid 5 mg, vitamin B12 1 mg, and vitamin B6 25 mg daily for 18 months does not have a beneficial effect on cognitive function or the severity of disease when compared with placebo (50319). However, all patients in this study were also consuming a folate-fortified diet.
• Angioplasty. Oral folic acid has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: Some evidence suggests that folic acid 1 mg, vitamin B12 400 mcg, and pyridoxine 10 mg daily can decrease the rate of restenosis in patients treated with balloon angioplasty (8009,9412). However, this combination does not seem to be as effective for reducing restenosis in patients after coronary stenting (8009). An intravenous loading dose of folic acid, vitamin B6, and vitamin B12 followed by oral administration of folic acid 1.2 mg, vitamin B6 48 mg, and vitamin B12 60 mcg daily after bare metal coronary stenting also does not seem to reduce restenosis and might actually increase restenosis (12150,12151). Due to the lack of evidence of benefit and potential for harm, this combination of vitamins should not be recommended for patients receiving coronary stents (12151).
• Atopic dermatitis (eczema). It is unclear if oral folic acid during pregnancy reduces the risk of eczema in the child. Details: Observational research has found that consuming both iron and folic acid supplements during pregnancy is associated with a four-fold reduced risk for developing atopic dermatitis in the child. However, use of either iron or folic acid supplementation alone is not associated with an effect on the child's risk for atopic dermatitis (102387).
• Autism spectrum disorder. It is unclear if oral folic acid intake during pregnancy reduces the risk of autism spectrum disorder in the child. Details: A meta-analysis of population research has found that consumption of folic acid of at least 400 mcg daily from both diet and supplements during pregnancy is associated with a 45% reduced risk of autism in the child at 2-15 years of age. Also, supplementation with folic acid during the prenatal to early period of pregnancy is associated with an approximate 43% reduced risk of autism in the child. This association did not differ between countries with or without a folate fortification program (109198). An individual population study has also found that prenatal folic acid supplementation initiated the first day of the last menstrual period before conception is associated with a 39% reduced odds of autism in the child at age 3.3-10.2 years when compared to pregnancies without folic acid supplementation (91324).
• Beta-thalassemia. There is limited evidence on the oral use of folic acid for beta-thalassemia minor. Details: Patients with beta-thalassemia minor may experience decreased muscle strength and increased bone or muscle pain. A small clinical study in children with this condition shows that taking folic acid 1 mg, with or without L-carnitine 50 mg/kg, daily for 3 months reduces bone pain by 64% to 84% and increases the number of stairs climbed by 2- to 5-fold when compared with baseline (90631). The validity of this finding is limited by the lack of a control group.
• Bipolar disorder. It is unclear if adding oral folic acid to conventional bipolar therapy further improves symptoms. Details: Some clinical evidence suggests that folic acid does not improve the antidepressant effects of lithium in patients with bipolar disorder (50566). However, other clinical evidence suggests that taking folic acid in combination with valproate during the acute phase of mania improves the effects of valproate (50357).
• Breast cancer. It is unclear if oral folic acid reduces breast cancer risk. Details: Some older population research suggests that increased intake or levels of folic acid alone does not affect the risk of breast cancer or breast cancer-related mortality (50218,50224). However, in a specific group of women who also consume high amounts of dietary methionine, cyanocobalamin (vitamin B12), or pyridoxine (vitamin B6), dietary intake of folate is associated with a reduced risk of breast cancer (9328,50224). Also, more recent population research has found that folic acid plus folate dietary intakes between 153-400 mcg are associated with a reduced risk of breast cancer. This risk is further reduced in those who drink relatively large amounts of alcohol (90794). Folate intakes greater than 400 mcg daily do not appear to be protective against breast cancer (90794).
• Cancer. It is unclear if oral folic acid prevents cancer. Details: A large cohort study of children born to mothers with epilepsy on antiseizure medications suggests that prenatal folic acid exposure of 1 mg daily or more, at an average of 4.3 mg daily, is associated with a 2.7-fold greater risk of pediatric cancer when compared with children born to mothers with epilepsy but without prenatal exposure to high-dose folic acid. Additionally, this risk is not present in children of mothers without epilepsy taking high-dose folate (112103). It is unclear how maternal epilepsy, antiseizure medications, and folate interact to increase the risk of pediatric cancers. However, in the absence of clear guidelines, mothers with epilepsy should take no more than 4 mg of folic acid daily (112101,112102).
• Cardiovascular disease (CVD). Although oral folic acid does not seem to prevent most CVD events, some research suggests that increased dietary folic acid might lower the risk of stroke and CVD-related mortality in patients at high risk for CVD. Details: In 2001, prior to the publication of the highest quality research on this topic, the US Food and Drug Administration (FDA) approved a qualified health claim stating that, as part of a well-balanced diet that is low in saturated fat and cholesterol, folic acid, vitamin B6, and vitamin B12 may reduce the risk of vascular disease (102368). Meta-analyses of available research show that folic acid might lower the risk of stroke in patients with CVD (97619,102386,107136). Some clinical research shows that taking folic acid reduces the risk of CVD by 15% in patients with kidney failure or chronic kidney disease (50444,91311). However, most research shows that folic acid supplementation, alone or in combination with vitamin B6 and vitamin B12, does not improve endothelial function or reduce the risk of death or CVD events in patients with existing hyperhomocysteinemia, coronary heart disease, CVD, kidney disease, or prior stroke, despite having a homocysteine-lowering effect (9313,9322,11337,11387,13482,50437) (50512,50527,96154,96147,97619,102386). Some population research has evaluated adults at high risk for CVD. This research has found that dietary folate intake of at least 382 mcg daily is associated with a modest reduction in CVD-related mortality and possibly all-cause mortality. Consuming folic acid as a component of fortified food in doses of more than 251 mcg daily is associated with a modest reduction in CVD-related mortality. Conversely, folic acid supplementation is associated with a higher risk of CVD and overall mortality, and there is a J-shaped association between folate intake, serum folate levels, and red blood cell folate levels, with both CVD-related and all-cause mortality (109199).
• Cervical cancer. It is unclear if oral folic acid prevents cervical cancer. Details: Epidemiological evidence has found that increasing folate intake from dietary and supplement sources, along with thiamine, riboflavin, and vitamin B12, might decrease the risk of precancerous cervical lesions (11074).
• Child development. It is unclear if oral folic acid supplementation during pregnancy improves child development. Details: Clinical research in Northern Ireland shows that taking folic acid 400 mcg daily starting in the 14th week of gestation and continuing until the end of pregnancy improves word reasoning in the child at 7 years of age when compared with placebo. When compared with a historical cohort from Britain, folic acid supplementation was associated with an increase in full scale IQ, verbal IQ, performance IQ, and general language at 7 years of age (102385). At age 11, benefits in word reasoning were no longer significant. However, there were modest benefits in some measures of processing speed when compared with placebo. Verbal comprehension was modestly improved in females, but not males (109192). Observational research in pregnant individuals and their children in Spain has found that taking less than 400 mcg of folic acid daily during pregnancy is associated with lower mental alertness scores in children at ages 7-9 years when compared with folic acid 400-999 mcg daily, while taking folic acid 1000 mcg or more daily during pregnancy was associated with improvements in some measures of working memory in the children. However, no relationship between folic acid dosing and most other measures of cognitive function was identified (110449).
• Chronic fatigue syndrome (CFS). Although there is interest in using oral or injectable folic acid for CFS, there is insufficient reliable information about the clinical effects of folic acid for this condition.
• Chronic kidney disease (CKD). While adding oral folic acid to enalapril might slow CKD progression, adding folic acid to high-dose vitamin B12 does not seem to be beneficial. Details: Clinical research in adults with hypertension and CKD shows that taking enalapril with folic acid 800 mcg for a median of 4.4 years reduces the risk of worsening kidney function by 21% and slows the rate of kidney function decline by 44% when compared with enalapril alone (96153). However, clinical research does not support the use of folic acid in patients with CKD when used in combination with high-dose vitamin B12 (cyanocobalamin). Vitamin B12 might increase the risk of negative outcomes (50253,50409,96150). More research is needed to determine the benefits of folic acid when used alone.
• Colorectal cancer. It is unclear if oral folic acid prevents colorectal cancer. Details: Although the majority of population research suggests that taking folic acid orally from dietary and supplemental sources reduces the risk of colorectal cancer (505,2140,2144,2145,2250,6271,9325,9326,50109,50427,50450)(91306,91323,96160,109188,110450), clinical evidence in general is not supportive. Most clinical research and meta-analyses of clinical trials suggest that taking folic acid from dietary or supplemental sources does not reduce the risk of colorectal cancer (2141,34596,50394). The reason for this discrepancy is unclear. Some observational research suggests that an inverse association between folate intake and risk of colorectal cancer was not apparent until at least 12 years after baseline folate intake was determined (109188). A meta-analysis of observational studies suggests that the benefits of folic acid supplementation on colorectal cancer risk might be limited to patients with moderate to high alcohol consumption (110450). Other clinical evidence suggests that the beneficial effect of folic acid may be limited to colon, but not rectal, cancer (21501). Furthermore, the beneficial effect for colon cancer may be limited to only certain subtypes. For instance, females with folate intake of at least 400 mcg daily seem to have a 46% reduction in the risk of p53-overexpressing colon cancer, but not p53-negative tumors, when compared with those who consume less than 200 mcg daily (21300). Also, the source of folic acid may influence its effects. Some observational research suggests that dietary folate, but not folic acid supplementation, reduces the risk of colon cancer (21501).
• Congenital heart disease. It is unclear if oral folic acid prevents congenital heart disease. Details: The exact cause of congenital heart disease is unknown but is thought to be a combination of genetic and environmental factors. Population research has found that supplementation with folic acid or folic acid-containing prenatal vitamins during pregnancy is associated with up to a 40% lower risk of congenital heart defects in newborns (99373).
• Dementia. It is unclear if oral folic acid is beneficial for the prevention or treatment of dementia. Details: While some preliminary research shows that folic acid might aid in the prevention and treatment of Alzheimer disease (13165,15270,50246,90374), two small clinical trials show that taking folic acid 15-20 mg daily for 10-12 weeks does not seem to improve cognitive function or the severity of dementia in patients with various forms of dementia, including vascular dementia, Lewy body dementia, probable Alzheimer disease, or dementia due to other causes (50062,50597).
• Diabetes. Small clinical studies suggest that oral folic acid does not improve glycemic control. Details: Meta-analyses of small clinical trials in patients with type 2 diabetes show that folic acid does not reduce glycated hemoglobin (HbA1C) when compared with placebo (50528,109197). Another small clinical study in patients with diabetes who are stabilized on metformin and/or a sulfonylurea shows that taking folic acid 5 mg daily for 8 weeks does not affect HbA1C when compared with placebo (104917). The validity of this study is limited by its small size and lack of blinding. Conversely, a meta-analysis of clinical research shows that taking folate modestly reduces fasting blood glucose and insulin levels, as well as measures of insulin resistance, when compared with placebo or no intervention (109197). There was no clear relationship between these changes and the dose or duration of folate. However, the studies included in this analysis evaluated multiple patient populations; the effect of folate in patients with diabetes, specifically, is unclear. Beyond glycemic control, some research has assessed the impact of dietary folate intake on cardiovascular risk in patients with diabetes. An observational study in Chinese adults with type 2 diabetes has found that dietary intake of folate in the highest quartile is associated with 68% lower odds of developing cardiovascular disease, defined as a non-fatal myocardial infarction, non-fatal stroke, or hospitalization for unstable angina, when compared with folate intake in the lowest quartile (110452). Folic acid has also been evaluated in gestational diabetes. A meta-analysis of 20 studies shows that serum and red blood cell (RBC) folate levels are higher in patients with gestational diabetes than without gestational diabetes. Subgroup analysis suggests that patients with gestational diabetes have higher serum and RBC folate levels in the second trimester than in those without gestational diabetes, while RBC folate levels in patients with gestational diabetes were higher in the first trimester than those without gestational diabetes. Overall, higher serum folate levels are associated with a slight increase in the odds of gestational diabetes when compared with lower serum folate levels (112107).
• Diabetic neuropathy. Oral folic acid has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: Preliminary clinical research in patients with diabetic neuropathy shows that taking a combination of B vitamins, including folic acid (L-methylfolate), vitamin B12 (methylcobalamin), and vitamin B6 (pyridoxal-5'-phosphate), for 24 weeks does not improve neural dysfunction based on vibration perception, but does seem to improve total neuropathy symptoms, when compared with placebo. These symptoms, which include both sensation and pain, decreased by 25% with the B vitamin combination, compared with only 15% in those taking placebo (90375).
• Epilepsy. It is unclear if oral folic acid reduces seizure frequency. Details: A meta-analysis of preliminary clinical research shows that taking folic acid does not reduce seizure frequency in patients with epilepsy (50124). However, there is some speculation that folate deficiency might be linked to increased seizure frequency. A preliminary clinical study in folate-deficient children with epilepsy shows that taking folic acid 5 mg daily for 3 months reduces seizure frequency when compared to baseline, but not when compared with a control group that is not deficient in folate (99371).
• Erectile dysfunction (ED). Oral folic acid has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: A very small clinical study in males with mild erectile dysfunction, overweight or obesity, and normal to low androgen levels shows that taking a combination product containing folic acid 400 mcg, alpha-lipoic acid, myo-inositol, and apple (Sinopol Forte, Laborest) improves measures of erectile dysfunction when compared to baseline (111674). The validity of these effects is limited by the small sample size and the lack of a comparator group, and it is unclear if these effects are due to folic acid, other ingredients, or the combination.
• Esophageal cancer. Higher dietary folate intake is associated with a lower risk of esophageal cancer. Details: One meta-analysis of observational research has found that higher levels of dietary folate are associated with a 34% lower risk of esophageal squamous cell carcinoma and a 50% lower risk of esophageal adenocarcinoma when compared with low levels of dietary folate (50208). Another meta-analysis of observational research has found that consuming high amounts of folate is associated with a 36% decrease in the odds of esophageal cancer when compared with lower dietary folate intake (100950).
• Fenofibrate (Tricor)-induced hyperhomocysteinemia. Folic acid seems to attenuate increases in homocysteine in people taking fenofibrate. Details: A small open-label clinical trial in patients taking fenofibrate shows that adding folic acid 10 mg every other day might reduce elevated plasma homocysteine levels by up to 59% when compared with taking fenofibrate alone (9321).
• Gastric cancer. It is unclear if oral folic acid reduces gastric cancer risk. Details: Observational research has found that taking folic acid reduces the risk of gastric cardia adenocarcinoma by 17% and the risk of noncardia gastric cancer by 33%, but does not reduce the risk of gastric cancer overall (50208). Also, a meta-analysis of 13 small clinical studies in patients with gastric precancerous conditions shows that taking folic acid 20-30 mg daily for 3-6 months improves gastric mucosal atrophy and intestinal metaplasia but does not seem to improve symptoms when compared with a control (110448). Whether these findings are associated with a lower risk of gastric cancer is unclear.
• Gout. It is unclear if oral folic acid reduces the risk for gout. Details: An observational study has found that increased dietary folate intake is associated with a lower incidence of gout (50454).
• Head and neck cancer. It is unclear if oral folic acid is beneficial for head and neck cancer prevention. Details: Population research has found that the highest intake of dietary folate is associated with a 50% reduced risk of head and neck cancer when compared with the lowest intake of folate. Each 100 mcg increase per day seems to reduce the risk by about 4% (96151).
• Hearing loss. It is unclear if oral folic acid prevents hearing loss. Details: Low levels of serum folate seem to be a risk factor for sudden sensorineural hearing loss in adults (21283). Observational research in females has found that serum folate levels in the lowest quintile are associated with a 19% increased risk for hearing loss when compared with levels in the second quintile. Also, folate levels in the highest quintile are associated with a 12% lower risk of hearing loss when compared with the second quintile (109807). A clinical study in older adults from the Netherlands shows that taking folic acid 800 mcg daily for 3 years slows the decline of age-related low-threshold hearing loss when compared with placebo (15163). However, at the time of this study, folate enrichment of foods was not allowed in the Netherlands. As a result, baseline folate levels in this study population were about 50% lower than in the US population. The effect of folic acid supplementation in people with higher baseline folate levels is unclear.
• Infertility. It is unclear if oral 5-methyltetrahydrofolate (5-MTHF) in combination with vitamin B6 and vitamin B12 is more beneficial than folic acid alone for increasing pregnancy rate in females undergoing assisted reproductive technology (ART). Details: Retrospective research from Italy suggests that taking 5-MTHF 400 mcg, vitamin B12 5 mcg, and vitamin B6 3 mg daily results in clinical pregnancy and live birth rates of approximately 60% and 49%, respectively, compared with 45% and 35% of those taking folic acid 400 mcg daily. A sub-analysis suggests that beneficial effects on pregnancy rates are limited to individuals aged less than 40 years (109189). The findings from this study are limited by its retrospective design. Also, it is unclear if these findings are generalizable to countries with folate fortification.
• Kidney failure. It is unclear if oral folic acid is beneficial in patients with kidney failure. Details: Because hemodialysis removes folate from the body, there is concern that folate deficiency may cause complications in patients with kidney failure receiving hemodialysis. Observational research in Taiwanese patients with kidney failure undergoing hemodialysis has found that taking folic acid 5 mg daily for an average of 5.8 years is associated with a 31% lower risk of arteriovenous access thrombosis when compared with folic acid 5 mg weekly. However, daily folic acid supplementation was not linked to a lower risk of cardiovascular events, cancer, or mortality when compared with weekly folic acid (110120). Oral folic acid has also been evaluated in combination with other ingredients. A small, low-quality clinical study in adults with kidney failure undergoing regular hemodialysis shows that taking oral folic acid 30 mg daily with thiamine 90 mg daily for 96 weeks reduces overall mortality by 67% and improves cognitive scores by 31% when compared with no intervention (107724). It is unclear if these findings are due to folic acid, thiamine, or the combination.
• Lometrexol toxicity. While oral folic acid might reduce lometrexol toxicity, intravenous folic acid does not seem to help. Details: In a phase I trial, intravenous folic acid 5-25 mg administered 1 hour or 3 hours prior to lometrexol 15-30 mg/m2 every 3 weeks does not seem to reduce cumulative lometrexol toxicity (2161). However, in a phase II study, taking oral folic acid 3 mg/m2 daily in addition to lometrexol 10 mg/m2 weekly seems to attenuate cumulative toxicity and improve its tolerability in cancer patients (104948).
• Low birth weight. It is unclear if oral folic acid supplementation during pregnancy reduces the risk of a low birth weight. Details: Clinical research shows that supplementation with folic acid 200 mcg to 5 mg daily during pregnancy increases mean birth weight when compared with placebo (91307). Furthermore, some population research has found that pre- or peri-conception folic acid supplementation, usually 400 mcg daily, is associated with a reduced risk of a child born small-for-gestational age. However post-conception folic acid supplementation is not associated with reduced risk (91304,103983). An observational study in pregnant Chinese patients found that supplementation with folic acid is associated with a 20% lower odds of low birth weight when compared with no supplementation. This association was observed when folic acid was used both before conception and during pregnancy for at least 24 weeks or during pregnancy only for at least 12 weeks. Increased dietary folate intake was not linked to a lower risk of low-birth-weight infants (110446). However, other observational research has found no association between folic acid supplementation during pregnancy and the risk for small-for-gestational age births (110447).
• Lung cancer. It is unclear if oral folic acid reduces lung cancer risk. Details: There does not appear to be a relationship between deficiency of folate and lung cancer (9454). However, consuming at least 130.4 mcg of folate per 1000 kcal daily seems to reduce the risk of lung cancer by 40% in former smokers when compared to those with lower dietary folate intake (50065).
• Melanoma. It is unclear if oral folic acid reduces melanoma risk. Details: Population research has found that folic acid supplementation of 2-2.5 mg daily in combination with vitamin B6 and vitamin B12 is linked with a 53% reduced risk of melanoma (91312).
• Metabolic syndrome. Although there is interest in using oral folic acid for metabolic syndrome, there is insufficient reliable information about the clinical effects of folic acid for this condition.
• Nitrate tolerance. It is unclear if oral folic acid helps to prevent the development of tolerance to treatment with nitroglycerin. Details: Some clinical evidence suggests that taking folic acid 1 mg daily for 1 week does not prevent the development of nitroglycerin-induced endothelial dysfunction or tolerance in healthy individuals (50442). However, other research suggests that taking folic acid 10 mg daily for 1 week prevents nitric oxide synthase dysfunction caused by continuous nitroglycerin (9316).
• Nonalcoholic fatty liver disease (NAFLD). It is unclear if oral folic acid is beneficial for NAFLD. Details: A cross-sectional analysis suggests that adults with NAFLD have lower levels of serum folate and its major component 5-MTHF when compared with healthy controls. Additionally, adults with NAFLD seem to consume less supplementary and dietary folate when compared with healthy controls. Overall, serum folate levels are negatively associated with the risk of NAFLD, and inadequate folate intake is associated with an increased risk of NAFLD (112104).
• Oral clefts. It is unclear if oral folic acid reduces the risk of oral clefts in infants. Details: Observational research has found that maternal folic acid supplementation is associated with an up to 49% reduced risk of cleft lip with or without cleft palate (50220,104921). Furthermore, a large clinical trial in pregnancies at-risk for oral cleft suggests that taking a higher dose of folic acid 4 mg from pre-conception until the end of the first trimester results in a similar oral cleft recurrence rate of 2.5%, compared with a 2.9% recurrence with a lower dose of folic acid (400 mcg). Both doses demonstrate a lower incidence of oral clefts when compared with historical rates of 6.3% (91322). Although there is speculation that genetic markers of folate status impact the effect of folic acid on orofacial cleft incidence, the current data do not show a relationship (104921).
• Overall mortality. It is unclear if oral folic acid reduces the risk of overall mortality. Details: Observational research in US adults has found that dietary intake of folic acid in the highest quintile is associated with a 14% to 23% lower risk of all-cause mortality and a 41% to 47% lower risk of cardiovascular mortality when compared with the lowest quintile of dietary folic acid intake (110451).
• Pancreatic cancer. It is unclear if oral folic acid reduces pancreatic cancer risk. Details: Consuming greater than 280 mcg daily of dietary folate is associated with a decreased risk of exocrine pancreatic cancer (9327). A meta-analysis of case-control and cohort studies suggests that consuming higher amounts of dietary folate reduces the risk of pancreatic cancer by 51% compared to low levels of dietary folate (50208). However, another meta-analysis of prospective cohort studies suggests that folate/folic acid intake does not significantly affect the overall risk of pancreatic cancer (50499). The contradictory results may be associated with the form of intake or may be related to the gender of the participants. A meta-analysis of clinical research shows that dietary folate, but not folic acid, significantly reduces the risk of pancreatic cancer (50387). Also, one meta-analysis of observational studies has found that high dietary folate decreases the risk of pancreatic cancer in females, but not males (50387).
• Peripheral neuropathy. Oral folic acid has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: Preliminary clinical research shows taking a combination of folic acid 400 mcg, vitamin B12 3 mcg, and uridine monophosphate 50 mg daily (Keltican) for 60 days reduces pain associated with peripheral neuropathy. Use of this product reduces pain intensity by approximately 44%, with loss of burning pain in approximately 50% of patients, strong tingling or pricking in approximately 57% of patients, strong pain attacks in 92% of patients, and numbness in 90% of patients when compared with baseline. Radiating pain and the use of concomitant medications are also reduced (90384). The validity of this finding is limited by the lack of a comparator group. Furthermore, it is unclear if the benefits are due to folic acid, other ingredients, or the combination.
• Pharyngeal cancer. It is unclear if oral folic acid reduces pharyngeal cancer risk. Details: Population research has found that intake of folic acid and folate from natural, fortified, and supplemented sources, may protect against oropharyngeal cancer. Intake of at least 258-816 mcg total folate/folic acid reduces the odds by 35% when compared with intakes of less than 344 mcg. Furthermore, folate/folic acid may be more beneficial for oral cancer versus pharyngeal cancer and in heavy alcohol users versus non users or light users (91302).
• Polycystic ovary syndrome (PCOS). It is unclear if oral folic acid is beneficial for PCOS. Details: One clinical study in overweight or obese patients with PCOS shows that taking folate 1 mg or 5 mg daily for 8 weeks modestly reduces levels of homocysteine, as well as insulin resistance, when compared with placebo. However, only the 5 mg dose modestly reduces insulin, total cholesterol, and low-density lipoprotein (LDL) cholesterol levels. Neither dose appears to affect fasting plasma glucose, high-density lipoprotein (HDL) cholesterol, or triglyceride levels when compared with placebo (109200). Other clinical research in patients with PCOS taking metformin shows that taking folate 400 mcg daily for 6 months does not affect glycemic parameters, plasma lipid levels, or hormone levels when compared with placebo (109194). The reasons for discrepancies between studies are unclear but may relate to patient characteristics. One study included only overweight or obese individuals with at least two of the three PCOS criteria, whereas the other study limited enrollment to patients in any weight category but with all three PCOS criteria (109194,109200).
• Pregnancy-induced hypertension. It is unclear if oral folic acid reduces the risk of hypertension during pregnancy. Details: Population research has found that taking folic acid during pregnancy is not associated with a reduced risk of gestational hypertension (91308,99370,99372).
• Restless legs syndrome (RLS). Although there is interest in using oral folic acid for RLS, there is insufficient reliable information about the clinical effects of folic acid for this condition.
• Schizophrenia. Oral folic acid has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: Clinical research shows that taking a combination of folic acid 2 mg and vitamin B12 400 mcg daily for 16 weeks improves negative symptoms when compared with placebo in patients with schizophrenia who have persistent symptoms and a specific genetic variant of the folate transporter gene FOLHI. This variant normally results in reduced folate absorption. However, in patients without this genetic variant, folate is not beneficial with respect to negative symptom improvement (90387).
• Sickle cell disease. Oral folic acid has only been evaluated in combination with other B vitamins; its effect when used alone is unclear. Details: Preliminary clinical research in adults with sickle cell disease shows that taking vitamin B12 4.2-6 mcg, folic acid 700 mcg, and vitamin B6 4.2-6 mg daily might lower homocysteine levels. However, it is unknown if this will reduce the risk of endothelial damage in these patients (9324).
• Suicidal ideation. It is unclear if oral folic acid reduces the risk of suicidal ideation or suicide attempts. Details: One observational study has evaluated the association between folic acid supplementation and suicidal events in patients with various underlying conditions, including 12% with depression, 15% with anxiety, and 46% with pain. This within-person cohort study found that filling a prescription for folic acid 0.4-5 mg daily, either alone or as part of a multivitamin, is associated with a 44% reduced rate of suicidal events during the months after the prescription when compared with the months without the prescription. For the 48% of patients who received folic acid 1 mg daily, each additional month of taking the prescription was associated with a 5% decrease in suicidal events (109201). Prospective clinical research is needed to confirm any benefits of folic acid and to determine whether baseline folate deficiency plays a role in these outcomes. More evidence is needed to rate folic acid for these uses.

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LIKELY EFFECTIVE

• Dyslipidemia. Niacin prescription products, in doses of 500 mg or greater, are FDA-approved for primary hyperlipidemia and mixed dyslipidemia. Niacin dietary supplements are generally available in lower doses and have not been shown to improve lipid levels. Details: Prescription niacin is not routinely recommended as second-line therapy for patients who primarily need to decrease low-density lipoprotein (LDL) cholesterol. This is due to results from clinical trials showing no effect on cardiovascular related events or mortality (93346,93354,96208,96211,97308,97477,97336). However, niacin might be considered for patients with mixed hyperlipidemia or patients who need to increase high-density lipoprotein (HDL) cholesterol and lower triglycerides. Niacin might also be effective for isolated hypoalphalipoproteinemia (4817). The most pronounced increases in HDL and decreases in triglycerides occur at 1-1.5 grams daily, and the greatest LDL reduction occurs at 2-3 grams daily. Niacin reduces LDL cholesterol by up to 25%, compared with up to a 55% reduction with statins. High-dose niacin can also decrease triglycerides by 20% to 50%, increase HDL by 13% to 35%, decrease apolipoprotein B levels by 2% to 20%, and decrease lipoprotein(a) levels by 23% (4818,4886,4887,4888,4889,4890,12033,25567,93347,96213). The effects of higher dose extended-release niacin on LDL cholesterol and triglycerides appear to be greater in females than males (25565). Experts recommend maximizing statins first because they have the best evidence for improving cardiovascular outcomes (97477,97336,97337). However, if patients cannot reach their LDL goal with a statin alone or if they cannot tolerate a statin, niacin might be combined with other cholesterol-lowering drugs when diet and single-drug therapy are not adequately effective (8545,25566,93351,94191,97337). Adding low-dose niacin, 50 mg daily, to statin therapy has no additional benefit on lipid levels (8546). Population research in adults without dyslipidemia has also found that higher dietary intake of niacin for 3-10 years is associated with a 29% lower risk of developing dyslipidemia when compared with low dietary niacin intake (110493).
• Pellagra. Oral niacin is FDA-approved for the prevention and treatment of pellagra. Details: Population research has found that low consumption of niacin is associated with an increased risk of developing pellagra (25903). Taking niacin 500-1000 mg daily can resolve symptoms of pellagra within a week of treatment initiation (25904). However, niacinamide is sometimes preferred for this indication because it lacks the vasodilating effects of niacin (15,6243).

POSSIBLY EFFECTIVE

• HIV/AIDS-related dyslipidemia. Oral niacin seems to improve lipid levels in patients with dyslipidemia due to HIV/AIDs. Details: Small clinical trials in HIV patients with dyslipidemia associated with antiretroviral therapy shows that taking extended-release niacin (Niaspan, Abbott Laboratories) titrated up to 2 grams daily for 14-48 weeks improves total cholesterol, high-density lipoprotein (HDL) cholesterol, and triglyceride levels when compared to baseline (25570,25902). Other preliminary clinical research in this population shows that taking extended-release niacin (Niaspan, Abbott Laboratories) titrated to 2 grams daily for up to 2 years improves HDL cholesterol levels, but not total cholesterol or triglyceride levels, when compared with no treatment (25569).
• Metabolic syndrome. Oral niacin seems to improve lipid levels in patients with metabolic syndrome. Details: Clinical research shows that taking niacin (Niaspan, Abbott Laboratories) 2 grams daily orally for 16 weeks reduces triglyceride levels by 39 mg/dL and increases high-density lipoprotein (HDL) cholesterol by 5 mg/dL when compared to baseline in patients with metabolic syndrome. These improvements are significant when compared with placebo and are further increased when niacin is taken along with prescription omega-3 ethyl esters (Lovaza, GlaxoSmithKline Pharmaceuticals) 4 grams daily orally (93353). However, niacin does not seem to improve postprandial glucose levels in patients with metabolic syndrome (97333).

INEFFECTIVE

• Cardiovascular disease (CVD). Oral niacin does not seem to reduce cardiovascular-related events in patients with or without CVD. Details: Overall, niacin is not recommended for primary or secondary prevention of CVD. Most clinical trials and meta-analyses conducted prior to 2011 showed a reduction in cardiovascular-related events, cardiovascular-related mortality, and all-cause mortality in patients taking niacin alone or in combination with a statin or clofibrate for primary or secondary prevention of CVD (4847,7388,25095,25911,25912,93349). However, recent meta-analyses of these studies and additional moderate-to-high quality research conducted in over 39,000 patients show no effect of niacin on cardiovascular-related events, cardiovascular-related mortality, or overall mortality (93346,93354,96208,96211,97308). Additionally, one meta-analysis shows that patients taking niacin are twice as likely to report side effects when compared with placebo (96211).

INSUFFICIENT RELIABLE EVIDENCE to RATE

• Alzheimer disease. It is unclear if oral niacin is beneficial for reducing Alzheimer disease risk. Details: Observational research has found that consuming higher amounts of niacin (17-45 mg daily) from food and supplements is associated with a slower cognitive decline and a lower risk of developing Alzheimer disease when compared with people who consume less niacin (14 mg daily) (12077). It is not known if the risk of Alzheimer disease is reduced by taking a stand-alone niacin supplement.
• Atherosclerosis. It is unclear if oral niacin prevents atherosclerosis progression. Details: Preliminary clinical studies show that taking niacin orally, in combination with colestipol for up to 2 years, might modestly reduce progression of atherosclerosis as measured by coronary lesions and carotid arterial intima-media thickness in high-risk males with existing coronary atherosclerosis (25906,25909,25910). However, niacin does not seem to be better than statins. One clinical study in adults with atherosclerosis and peripheral arterial disease shows that taking extended-release niacin 1500 mg, simvastatin 40 mg, and ezetimibe 10 mg daily for 2 years does not reduce atherosclerosis of the superficial femoral artery when compared with simvastatin alone (96208). Niacin has also not been shown to prevent cardiovascular events or mortality (93346,93354,96208,96211,97308).
• Athletic performance. It is unclear if oral niacin improves athletic performance. Details: Preliminary clinical research in untrained adult males shows that taking niacin 1000 mg orally once before a cycling test does not improve power, respiratory exchange ratio, or time to exhaustion when compared with placebo. In addition, these measures were significantly worse when compared with taking caffeine 5 mg/kg orally as a single dose (107942). Clinical research in untrained males also shows that taking a supplement containing niacin 40 mg, caffeine 400 mg, capsicum extract 66.7 mg, and black pepper extract 10 mg prior to exercising does not improve strength, time to exhaustion, or maximal oxygen consumption when compared with placebo (37873).
• Attention deficit-hyperactivity disorder (ADHD). Although there is interest in using oral niacin for ADHD, there is insufficient reliable information about the clinical effects of niacin for this condition.
• Cancer. It is unclear if dietary niacin is beneficial for cancer. Details: Population research in adults with cancer has found that high dietary niacin intake is associated with 49% and 27% lower risk of cancer-related mortality and all-cause mortality when compared with low dietary niacin intake. The same study also found that taking niacin supplements is associated with a lower risk of cancer-related mortality, but not all-cause mortality when compared with not taking niacin supplements (110496).
• Cataracts. It is unclear if oral niacin is beneficial for preventing cataracts. Details: Population research has found that high dietary intake of niacin is associated with a reduced risk of nuclear cataracts (6378). However, there is no reliable evidence that niacin supplements reduce the risk of cataracts.
• Cholera. It is unclear if oral niacin is beneficial for cholera. Details: One small clinical study in adults with severe cholera shows that taking 1-2 grams niacin orally reduces fluid loss in the stool by 31% to 47% in the first 16 hours when compared with control. The 2 gram dose seemed to result in a greater reduction in fluid loss than the 1 gram dose (4868).
• Erectile dysfunction (ED). It is unclear if oral niacin is beneficial in patients with ED and dyslipidemia. Details: Clinical research in patients with erectile dysfunction and dyslipidemia shows that taking extended-release niacin (Niaspan, Abbott Laboratories) titrated to 1.5 grams nightly for a total of 12 weeks significantly improves penetration frequency and the maintenance of an erection after penetration when compared to baseline (25913). The validity of this finding is limited by the lack of a comparator group.
• Glaucoma. It is unclear if oral niacin is beneficial for preventing or treating glaucoma. Details: Population research has found that higher dietary intake of niacin is associated with a lower odds of having glaucoma. However, this association was not consistently present when adjusting for confounders. The effects of niacin supplementation on glaucoma have not been evaluated (107942).
• Hyperphosphatemia. It is unclear if oral niacin is beneficial for preventing high levels of phosphorus in the blood. Details: Preliminary clinical research in patients on maintenance dialysis who are no longer using phosphate binders shows that taking niacin 375-750 mg daily for 8 weeks reduces serum phosphorus levels by 2.1 mg/dL, increases calcium levels by 0.4 mg/dL, and decreases serum alkaline phosphatase when compared with baseline (25914). However, clinical research in hemodialysis patients with inadequate phosphate control despite using standard phosphate-binding therapy shows that taking niacin at the maximum tolerated dose, up to 1000 mg daily, for 12 weeks, does not decrease serum phosphate levels when compared with placebo (93341). It is possible that this latter study was too small to observe between-group differences in changes in serum phosphate levels.
• Hypertension. It is unclear if dietary niacin is beneficial for preventing hypertension. Details: Observational research in Chinese adults found a J-shaped association between dietary niacin intake and development of hypertension, with the lowest risk occurring in those with a daily dietary niacin intake of 14.3-16.7 mg (104934).
• Meniere disease. Although there is interest in using oral niacin for Meniere disease, there is insufficient reliable information about the clinical effects of niacin for this condition.
• Migraine headache. It is unclear if dietary niacin is beneficial for preventing migraine headaches. Details: Population research in adults has found that high dietary intake of niacin is associated with a 28% lower likelihood of having migraine headaches when compared with low dietary intake of niacin (110495). However, the effect of niacin supplementation on migraines has not been studied.
• Motion sickness. Although there is interest in using oral niacin for motion sickness, there is insufficient reliable information about the clinical effects of niacin for this purpose.
• Parkinson disease. It is unclear if oral niacin is beneficial for improving Parkinson disease symptoms. Details: Low-quality clinical research in adults with Parkinson disease shows that taking slow-release niacin 250 mg orally daily for 12 months improves Parkinson disease motor scores and fatigue scores by 17% and 26%, respectively, when compared with baseline (107944). However, higher quality clinical research shows that taking niacin 250 mg orally daily for 6 months does not improve Parkinson disease motor scores when compared with placebo (107943).
• Retinal vein occlusion. It is unclear if oral niacin is beneficial for improving retinal vein occlusion symptoms. Details: A small case series in patients with chronic retinal vein occlusion shows that taking niacin titrated to 500 mg three times daily for 1 year is associated with reduced central macular thickness and improved visual acuity in over 50% of patients when compared with a control group. The addition of prednisolone eye drops does not alter the outcomes of those taking niacin (96212). The validity of this finding is limited due to the retrospective nature of this study.
• Sickle cell disease. It is unclear if oral niacin is beneficial for improving lipid levels in patients with sickle cell disease. Details: A small clinical study in patients with sickle cell disease shows that taking extended-release niacin titrated to 1.5 grams daily for 12 weeks does not improve vascular function or increase high-density lipoprotein (HDL) or apolipoprotein A-I cholesterol levels when compared with placebo (96209).
• Schizophrenia. Although there is interest in using oral niacin for schizophrenia, there is insufficient reliable information about the clinical effects of niacin for this condition.
• Vertigo. Although there is interest in using oral niacin for vertigo, there is insufficient reliable information about the clinical effects of niacin for this condition. More evidence is needed to rate niacin for these uses.

(Read more about NIACIN)

POSSIBLY EFFECTIVE

• Age-related cognitive decline. Oral bovine cortex-derived phosphatidylserine seems to improve attention and memory in patients with age-related cognitive decline. It is unclear if plant-derived phosphatidylserine is beneficial or whether phosphatidylserine is beneficial for preventing cognitive decline. Details: Clinical studies in people with age-related cognitive decline show that phosphatidylserine improves attention, arousal, verbal fluency, and memory (2440,2441,7119,7120,15539). Bovine- and plant-sourced phosphatidylserine 100 mg three times daily for up to 6 months has been used in these studies (2440,2441,15539). Most clinical studies have used phosphatidylserine derived from bovine cortex. However, most supplements now use soy- or cabbage-derived phosphatidylserine. There is some preliminary evidence that plant-derived phosphatidylserine also improves memory in people with age-associated memory impairment (15539). Also, clinical research in elderly females with complaints of memory loss shows that taking 1-3 capsules of a specific product (Vayacog, Enzymotec Ltd.) containing soybean-derived phosphatidylserine 100 mg/capsule, enriched with docosahexaenoic acid (DHA) 19.5 mg/capsule and eicosapentaenoic acid (EPA) 6.5 mg/capsule, daily for 15 weeks modestly improves immediate memory and sustained attention when compared with placebo (66055,90711). A post-hoc analysis of the results from this study suggests that cognitive improvements are greatest in patients with relatively good cognitive performance at baseline (66055). There is also interest in using phosphatidylserine to prevent age-related cognitive decline. In 2003, the US Food and Drug Administration (FDA) determined that it would allow a qualified health claim stating that consuming phosphatidylserine may reduce the risk of developing age-related cognitive decline. However, the FDA has determined that there is very little scientific evidence supporting this claim (102363).
• Alzheimer disease. Oral bovine cortex-derived phosphatidylserine seems to improve cognitive function and behavior in patients with Alzheimer disease when used for up to 12 weeks, although benefits may disappear after 16 weeks. It is unclear if plant-derived phosphatidylserine is beneficial. Details: Taking phosphatidylserine orally can improve cognitive function and global improvement rating scales and improve behavioral rating scales over 6-12 weeks of treatment (2255,2437,2438,2439,7114,7118). Bovine-sourced phosphatidylserine 300-400 mg in divided doses daily for up to 16 weeks has been used (2255,2437,2438,2439). Phosphatidylserine seems to be most effective in patients with less severe symptoms (2437,2439). Phosphatidylserine might lose its effectiveness with extended use. After 16 weeks of treatment, progression of Alzheimer disease seems to overcome any benefit of phosphatidylserine (2255). Most clinical studies have used phosphatidylserine derived from bovine cortex. However, most supplements now use soy- or cabbage-derived phosphatidylserine. Clinical studies have not yet evaluated phosphatidylserine from soy or other sources. It is not known if phosphatidylserine from these sources is as effective as bovine-derived products.

INSUFFICIENT RELIABLE EVIDENCE to RATE

• Athletic performance. It is unclear if oral phosphatidylserine is beneficial for athletic performance. Details: One small clinical trial in golfers shows that taking nutritional bars containing phosphatidylserine 200 mg daily for 6 weeks improves the number of good ball flights, which may improve golf score; however, perceived stress levels and heart rate are not significantly affected (68855). A clinical study in recreationally active adults shows that taking phosphatidylserine 400 mg and caffeine 100 mg daily, along with niacin 28 mg, vitamin C 60 mg, vitamin B1 1.5 mg, vitamin B5 10 mg, vitamin B6 2 mg, vitamin E 12 IU, calcium 100 mg, magnesium 40 mg, and carbohydrates in the form of evaporated cane juice, brown rice syrup, and rice syrup solids 16 grams (Nutravail Technologies) for 14 days modestly reduces post-exercise mood disturbances and perception of fatigue when compared with vitamins and minerals alone. The combination does not appear to improve cognitive function or reaction time (91463). It is not clear if the effect of the combination supplement is due to phosphatidylserine, caffeine, or the combination.
• Attention deficit-hyperactivity disorder (ADHD). It is unclear if oral phosphatidylserine is beneficial for ADHD. Details: A meta-analysis of three generally low-quality randomized clinical trials shows that taking phosphatidylserine 200-300 mg daily for 8-15 weeks modestly improves symptoms of inattention in children with ADHD when compared with placebo. However, there were no significant effects on hyperactivity-impulsivity or on overall ADHD symptoms. Also, two of the three clinical trials included in the analysis investigated the effects of phosphatidylserine in combination with the omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) (105247). One preliminary clinical trial included in the analysis shows that taking soy-derived phosphatidylserine 200 mg daily for 2 months improves ADHD symptoms, including inattention, hyperactivity-impulsivity, and short-term memory, when compared to baseline in treatment-naïve children with ADHD aged 4-14 years. However, results from this study are limited due to a lack of statistical comparison to the placebo group (89498).
• Cognitive function. Although there is interest in using oral phosphatidylserine for improving cognitive function in healthy adults, there is insufficient reliable information about the clinical effects of phosphatidylserine for this purpose.
• Dementia. It is unclear if oral phosphatidylserine is beneficial for dementia prevention or treatment. Details: In 2003, the FDA determined that it would allow a qualified health claim stating that consuming phosphatidylserine may reduce the risk of dementia in the elderly. However, the FDA has determined that there is very little scientific evidence supporting this claim (102363).
• Depression. It is unclear if oral phosphatidylserine is beneficial for depression. Details: One very small clinical study in elderly adults with depression shows that taking phosphatidylserine 300 mg daily for 30 days modestly improves depression scores when compared to baseline (7113).
• Exercise-induced muscle soreness. It is unclear if oral phosphatidylserine is beneficial for exercise-induced muscle soreness. Details: One small clinical study in athletes shows that taking soybean-derived phosphatidylserine 800 mg daily for 2 weeks during periods of over-training reduces muscle soreness post-exercise when compared with those not taking phosphatidylserine (2264). More evidence is needed to rate phosphatidylserine for these uses.

(Read more about PHOSPHATIDYLSERINE)

EFFECTIVE

• Phenylketonuria (PKU). Oral tyrosine as a component of medical foods is recommended in people with PKU, a disorder in which phenylalanine cannot be endogenously metabolized into tyrosine. Details: Tyrosine is used as a component of medical foods for people with phenylketonuria (PKU) (7212,7213,7232). Current guidelines recommend that people with PKU maintain a diet low in phenylalanine and incorporate tyrosine as a component of medical foods to maintain normal blood levels of tyrosine (95108). Supplementation with additional tyrosine is recommended only for patients with consistently low blood levels of tyrosine despite using tyrosine-containing medical foods (95108). Routine supplementation with free tyrosine is not recommended for most patients because it can produce wide variations in tyrosine plasma concentrations and side effects (7212,95108). Tyrosine intake does not improve neuropsychological measures in patients with PKU (81503,91471,95108).

POSSIBLY EFFECTIVE

• Cognitive function. Oral tyrosine might improve cognitive function, particularly in patients exposed to stressors such as excessive cold, noise, or sleep deprivation. Details: Most research suggests that taking tyrosine orally improves cognitive function, particularly under stressful conditions. Small clinical studies in healthy adults show that taking tyrosine 100-300 mg/kg in the setting of exposure to stressors such as excessive cold, noise, or sleep deprivation improves cognitive performance measures, such as executive function and short-term memory, when compared with placebo (7215,81472,81476,81484,81501). Other small clinical studies in healthy patients show that taking tyrosine 2 grams may improve response time without detracting from performance and could improve some measures of cognitive response to conflict when compared with placebo (101082,111248). Some of these small studies may be inadequately powered to detect an effect on some cognitive function tests. Tyrosine has also been evaluated in combination with other ingredients for this purpose. A small clinical study in healthy adults with fatigue shows that taking tyrosine, serine, alanine, glutamate, and aspartate daily for 4 weeks improves measures of cognitive function including attention, spatial cognition, orientation, motivation, and time management when compared with placebo (111249). It is unclear if these effects are due to tyrosine, other ingredients, or the combination.
• Memory. Taking tyrosine orally seems to improve memory in patients exposed to stressors such as cold or those having to complete multiple tasks at once. Details: Small clinical studies in healthy adults show that taking tyrosine 150-300 mg/kg prior to acute exposure to stress that is cold-induced, noise-induced, or induced by multi-tasking improves memory performance when compared with placebo (81469,81477,81499,81501). However, tyrosine 150 mg/kg does not seem to improve memory in less stressful situations such as performing one simple task or testing when not exposed to cold (81469,81499).

POSSIBLY INEFFECTIVE

• Athletic performance. Oral tyrosine does not improve athletic performance when taken prior to exercise. Details: Clinical studies show that taking tyrosine orally prior to participating in treadmill or cycling exercises conducted at temperate temperatures or in the heat does not improve strength, endurance, or performance when compared with placebo (81471,81474,81504,91470,104403). Another very small clinical study in healthy males shows that taking a multi-ingredient pre-workout supplement containing L-tyrosine, beta-alanine, L-citrulline maleate, arginine alpha-ketoglutarate, L-taurine, and caffeine does not increase bench press strength endurance when compared with equivalent amounts of anhydrous caffeine (111250).

INSUFFICIENT RELIABLE EVIDENCE to RATE

• Alcohol use disorder. Oral tyrosine has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: Preliminary clinical research in patients with alcohol use disorder shows that taking a combination of tyrosine 900 mg, D,L-phenylalanine 1.5 grams, L-glutamine 300 mg, and L-tryptophan 400 mg daily along with a multivitamin supplement reduces withdrawal symptoms and decreases stress when compared with placebo (81552). It is unclear if these effects are due to tyrosine, other ingredients, or the combination.
• Attention deficit-hyperactivity disorder (ADHD). It is unclear if oral tyrosine is beneficial for improving ADHD symptoms. Details: A very small clinical study shows that taking tyrosine does not improve symptoms of ADHD in children when compared with baseline (7209). Furthermore, another very small clinical trial in adults with ADHD shows that taking tyrosine daily for 8 weeks does not improve inattention when compared with baseline. Some patients might have transient symptom improvement after 2 weeks, but seem to acquire tolerance by 6 weeks (7210). The validity of these findings is limited by the small study size and lack of control groups.
• Cocaine dependence. Oral tyrosine has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: A small clinical trial in patients with cocaine dependence shows that taking L-tyrosine 1 gram in the morning and L-tryptophan 1 gram in the evening for 14 days does not reduce drug cravings or withdrawal symptoms when compared with placebo (81480).
• Dementia. Oral tyrosine has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: A very small clinical study in patients with severe Alzheimer disease or multi-infarct dementia shows that taking a combination of tyrosine 4 grams, 5-HTP 800 mg, and carbidopa 100 mg orally daily does not improve clinical or psychological parameters in most patients when compared with baseline (918). The validity of this finding is limited by the small study size and a lack of control group.
• Depression. It is unclear if oral tyrosine is beneficial for improving major depressive disorder. Details: A small clinical study in patients with major depression shows that taking L-tyrosine 100 mg/kg daily for 4 weeks does not improve depressive symptoms when compared with placebo (7208).
• Erectile dysfunction (ED). Although there is interest in using oral tyrosine for ED, there is insufficient reliable information about the clinical effects of tyrosine for this condition.
• Fatigue. Oral tyrosine has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: A small clinical study in healthy adults with fatigue shows that taking tyrosine, serine, alanine, glutamate, and aspartate daily for 4 weeks does not improve subjective or objective measures of fatigue when compared with placebo (111249).
• Hypertension. It is unclear if oral tyrosine is beneficial for reducing hypertension of mild severity. Details: A very small clinical study in patients with mild essential hypertension shows that taking oral tyrosine 2.5 grams three times daily with meals for 2 weeks does not affect systolic or diastolic blood pressure when compared with control (81487).
• Mitochondrial myopathies. Although there is interest in using oral tyrosine for nemaline myopathy, a type of mitochondrial myopathy, there is insufficient reliable information about the clinical effects of tyrosine for this condition.
• Narcolepsy. It is unclear if oral tyrosine is beneficial for improving narcolepsy symptoms. Details: A small clinical study in patients with narcolepsy shows that taking capsules containing tyrosine 3 grams orally three times daily for 4 weeks might reduce feelings of tiredness or drowsiness when compared with placebo, but the overall effect is not clinically significant. Tyrosine also does not seem to improve sudden muscle weakness, sleep paralysis, night-time sleep, sleep latency, or speed and attention after waking when compared with placebo (81482).
• Obesity. Oral tyrosine has only been evaluated for in combination with other ingredients; its effect when used alone is unclear. Details: A small clinical study in overweight or obese patients shows that taking a supplement containing tyrosine 1.2 grams, cayenne 450 mg, green tea 1.5 grams, caffeine 150 mg, and calcium carbonate 3.89 grams daily for 8 weeks slightly reduces body fat mass by 0.9 kg when compared with placebo (81475). It is not clear if any potential benefit is due to tyrosine, other ingredients, or the combination.
• Opioid withdrawal. Oral tyrosine has only been evaluated for heroin withdrawal in combination with other ingredients; its effect when used alone is unclear. Details: A small clinical study in Chinese males undergoing detoxification for heroin addiction shows that taking a combination of tyrosine 50 mg/kg, 5-HTP 200 mg, phosphatidylcholine 1200 mg, and L-glutamine 50 mg/kg daily for 6 days can reduce insomnia and withdrawal symptoms and improve mood when compared with placebo (88178). It is not clear if this effect is due to tyrosine, other ingredients, or the combination.
• Parkinson disease. Although there is interest in using oral tyrosine for Parkinson disease, there is insufficient reliable information about the clinical effects of tyrosine for this condition.
• Premenstrual syndrome (PMS). Although there is interest in using oral tyrosine for PMS, there is insufficient reliable information about the clinical effects of tyrosine for this condition.
• Schizophrenia. It is unclear if oral tyrosine is beneficial for improving schizophrenia symptoms. Details: A very small clinical study in patients with schizophrenia shows that taking L-tyrosine 10 grams daily in four divided doses along with molindone 150 mg daily for 3 weeks does not improve symptoms of schizophrenia when compared with taking molindone alone (81554).
• Sleep deprivation. It is unclear if oral tyrosine is beneficial for improving alertness in sleep deprived adults. Details: A small clinical study shows that taking tyrosine 150 mg/kg after the loss of a night's sleep seems to delay performance decline in psychomotor tests by about 3 hours when compared with placebo (7215). Another small clinical study in sleep-deprived patients shows that taking tyrosine 150 mg/kg improves memory, reasoning, and vigilance when compared with placebo at 5.5 hours after ingestion, but not at 1.5 hours. Tyrosine was less effective than taking amphetamine, phentermine, or caffeine (81472).
• Stress. Although there is interest in using oral tyrosine for stress, there is insufficient reliable information about the clinical effects of tyrosine for this condition.
• Wrinkled skin. Topical tyrosine has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: A small study in patients with photodamaged skin shows that applying a topical preparation containing 10% vitamin C, acetyl tyrosine, zinc sulfate, sodium hyaluronate, and bioflavonoids (High Potency Serum, Cellex-C International Inc.) for 3 months to the face seems to improve fine and coarse wrinkling, yellowing and sallowness, roughness, and skin tone when compared with placebo (6155). It is unclear if the benefits are due to tyrosine, other ingredients, or the combination. More evidence is needed to rate the effectiveness of tyrosine for these uses.

(Read more about TYROSINE)

EFFECTIVE

• Imerslund-Grasbeck disease. Intramuscular vitamin B12 is effective for patients with this condition. Details: Administering intramuscular vitamin B12 (hydroxocobalamin) 1 mg daily for 10 days, followed by monthly injections for the remainder of a patient's life, is effective for treating familial selective vitamin B12 malabsorption (Imerslund-Grasbeck disease) (15,82862).
• Vitamin B12 deficiency. Administering vitamin B12 orally, intramuscularly, or intranasally is effective for preventing and treating vitamin B12 deficiency. Details: Vitamin B12 deficiency has varying definitions but is often defined as vitamin B12 (cobalamin) levels less than 180-200 pmol/L (or 240 pg/mL). Some believe that only intramuscular vitamin B12 is effective for treating vitamin B12 deficiency. However, clinical research shows that oral therapy increases cobalamin levels similarly to intramuscular administration, even in patients with pernicious anemia or malabsorption, if a high enough dose is given (2909,2911,2915,9335,82832) (82836,82949,82860,103976,103972,107141,107144). Some evidence suggests that the most effective oral dose is between 647-1032 mcg daily (13106). However, in certain situations, intramuscular treatment might be more appropriate. Guidelines by the British Committee for Standards in Hematology recommend only intramuscular vitamin B12 for initial treatment of severe vitamin B12 deficiency in patients with pernicious anemia, malabsorption disorders, or neurological involvement (94722). Intramuscular vitamin B12 is also appropriate in patients with diarrhea or vomiting and those likely to be nonadherent (103972). Vitamin B12 deficiency is especially common in older adults, primarily due to lack of intrinsic factor and malabsorption (2915,2919,9335). Daily supplementation with vitamin B12 50-100 mcg might be needed to correct deficiency (10126), while daily doses of 25-37.5 mcg help to maintain normal levels over time (9335). In addition to supplements, foods such as milk and bread fortified with vitamin B12 can be used and are approximately 55% to 60% absorbed by people over 60 years of age (10124). Vitamin B12 deficiency is also common in patients that have had gastric surgery, including gastrectomy and bariatric surgery (107144,107145). Taking vitamin B12 in the doses found in multivitamins or generic vitamin B supplements does not seem to prevent vitamin B12 deficiency following bariatric surgery (107145). However, taking methylcobalamin 500 mcg daily is beneficial for treating vitamin B12 deficiency associated with a total gastrectomy and taking cyanocobalamin 5000 mcg daily is beneficial for preventing vitamin B12 deficiency following gastric bypass (107144). Other people at risk for vitamin B12 deficiency include strict vegetarians who eat no animal products (vegans) and people with increased vitamin B12 requirements associated with pregnancy, thyrotoxicosis, hemolytic anemia, hemorrhage, malignancy, and hepatic and kidney disease. Moderate consumption of animal products may not be sufficient to restore and maintain vitamin B12 levels, especially in adolescents who had consumed macrobiotic (vegan type) diets for the first 6 years of life. High dietary intake of vitamin B12 or supplements is usually needed in order to restore and maintain optimal vitamin B12 levels in these adolescents (10125).

LIKELY EFFECTIVE

• Cyanide poisoning. Intravenous hydroxocobalamin (Cyanokit) is likely effective as an antidote for patients with suspected or known cyanide toxicity due to inhalation, ingestion, or skin exposure. Details: Treatment of cyanide poisoning with hydroxocobalamin (Cyanokit) up to 10 grams has been approved by the US Food and Drug Administration (FDA) and recommended by the Australian Resuscitation Council (82870,82905,82906). Hydroxocobalamin is also FDA-approved for treating cyanide toxicity during pregnancy (82904).

POSSIBLY EFFECTIVE

• Canker sores. Sublingual or topical vitamin B12 seems to reduce canker sore symptoms. Details: Clinical research in patients with canker sores shows that applying a topical ointment containing vitamin B12 500 mcg in four divided doses daily for 2 days reduces pain levels by 80% when compared with a control ointment not containing vitamin B12 (96176). Other preliminary clinical research shows that taking vitamin B12 1000 mcg sublingually daily for 6 months reduces the duration of canker sore outbreaks, the number of ulcers, and level of pain when compared with placebo in patients with normal vitamin B12 levels (17242).
• Hyperhomocysteinemia. Oral vitamin B12 in combination with folic acid, and sometimes with vitamin B6, reduces homocysteine levels. Details: While folic acid 0.5-5 mg daily lowers fasting homocysteine levels by an average of 25%, adding vitamin B12 0.5 mg daily produces an additional decrease of about 7% on average (6883,9400,9401,9405,9409,50145,107136). Vitamin B12 in combination with folic acid and other vitamins also reduces homocysteine levels in patients with kidney failure, sickle cell disease, and those receiving nitrous oxide general anesthesia (1489,6883,6884,7289,7881,9324,9414,9415,9416,9481,82941). Some researchers recommend routine use of vitamin B12 with homocysteine-lowering regimens to avoid the risk of neuropathy in people with undetected vitamin B12 deficiency (9405). Using vitamin B12 alone has a limited effect on homocysteine levels, and probably only in those people with vitamin B12 deficiency (2147,9410,9512). Hyperhomocysteinemia is considered by some to be an independent risk factor for atherosclerosis, recurrent thromboembolism, deep vein thrombosis, myocardial infarction, and ischemic stroke (1899,2147,3323,9402,9405,9408,9409). Clinical research suggests that supplementation with folic acid, pyridoxine, and vitamin B12 decreases homocysteine levels and reduces the atherosclerosis progression in patients at risk for atherosclerosis when compared with placebo (50133,50056,82806). However, other research suggests that elevated homocysteine levels may be a marker, as opposed to a cause, of vascular disease (11387,11388). A 5 µmol/L increase in plasma homocysteine increases the risk of cerebrovascular disease by 50%, and the odds of coronary heart disease by 60% and 80% in males and females, respectively (9407,9411). However, it is not clear if reducing homocysteine levels results in reduced cardiovascular morbidity and mortality (1489,6883,6884,9400,9405,9409,96417). Folic acid, vitamin B6, and vitamin B12 supplementation can reduce total homocysteine from 13.4 to 11 µmol/L. However, this reduction does not seem improve endothelial function or help with secondary prevention of death or myocardial infarction, and some research even suggests an increase in cardiovascular disease (CVD) risk (11387,13482,50373,50314,97619). There is also some debate about whether supplementation with homocysteine-lowering B vitamins can reduce the risk of stroke. A number of large clinical studies and meta-analyses show that supplementation with folic acid, vitamin B6, and vitamin B12, alone or in combination, does not reduce the risk of stroke in patients with CVD or impaired kidney function (11387,13482,50423,83050,96150). However, a more recent meta-analysis of 10 clinical trials including over 44,000 patients shows that B vitamin supplementation reduces the relative risk of stroke by 10% when compared with placebo in patients at risk or with a history of CVD (97619). Also, a meta-analysis in adults with a history of stroke shows that B vitamin supplementation modestly reduces the relative risk of stroke recurrence by 13% and vascular death by 11% when compared with placebo (107136).
• Postherpetic neuralgia. Subcutaneous injections of vitamin B12 seem to reduce postherpetic neuralgia symptoms. Details: Clinical research in patients with subacute herpetic neuralgia shows that subcutaneous injection of vitamin B12 (methylcobalamin) 1000 mcg six times weekly for 4 weeks reduces pain when compared with oral vitamin B12 or subcutaneous lidocaine (90394). Another clinical study shows that administering local subcutaneous injections of methylcobalamin 1000 mcg plus lidocaine up to 20 mg daily for 12 injections over 14 days, starting within 7 days of the onset of subacute ophthalmic herpetic neuralgia, decreases the mean pain score by 63% to 79% when compared with intravenous lidocaine and intramuscular methylcobalamin. Less than 2 patients need to be treated to achieve a pain reduction to ≤3 out of 10. Healing of rash, itching, numbness, and tingling were also improved (96175). Additional clinical research in patients with postherpetic pain and itching shows that this same dosing regimen of subcutaneous vitamin B12 reduces pain and analgesic requirements when compared to baseline (90396).

POSSIBLY INEFFECTIVE

• Age-related cognitive decline. Oral vitamin B12 does not seem to improve cognitive function in older adults when used alone or in combination with other B vitamins. Details: Taking vitamin B12 100-1000 mcg plus folic acid 400-2000 mcg, with or without vitamin B6 3-50 mg, daily for up to about 2 years does not seem to improve tests of cognitive function in adults aged 65 or older, most of whom do not report cognitive impairment at baseline (14392,50225,50510,90392,107140). Also, supplementation with vitamin B12 does not seem to improve cognitive function in elderly individuals with low vitamin B12 levels (12305).
• Alzheimer disease. Oral vitamin B12, when used in combination with other B vitamins, does not seem to improve cognitive function in patients with Alzheimer disease. Details: Clinical research in patients with probable Alzheimer disease using routine medication shows that taking vitamin B12 1 mg, folic acid 5 mg, and vitamin B6 25 mg daily for 18 months does not have a beneficial effect on cognitive function or the severity of disease when compared with placebo. In this study, all patients were consuming a folate-fortified diet (50319). Also, a meta-analysis of clinical research in elderly adults with mild cognitive impairment or dementia shows that taking vitamin B12, usually with other B vitamins, does not improve cognitive function (50510). Observational research has also found that higher vitamin B12 intake over 3 years in a population consuming a folate-fortified diet is not associated with a decreased risk of developing Alzheimer disease (15270). In contrast, preliminary clinical research in patients with probable Alzheimer disease who are not consuming a folate-fortified diet shows that taking vitamin B12 50 mcg daily plus folic acid 1.2 mg daily for 6 months modestly improves some measures of cognitive performance and decreases levels of homocysteine when compared with placebo (107150). More research is needed to determine if any changes in this latter study are clinically relevant.
• Cataracts. Oral vitamin B12 does not seem to reduce cataract development. Details: Clinical research in women with existing cardiovascular disease (CVD) or at increased risk of CVD shows that taking a combination of folic acid 2.5 mg daily, vitamin B6 50 mg daily, and vitamin B12 1 mg daily for an average of 7.3 years does not reduce the risk of cataracts and seems to increase the risk of cataract extraction by 28% when compared with placebo (96149).
• Circadian rhythm sleep disorders. Oral vitamin B12 does not seem to improve sleep disorders. Details: Oral vitamin B12 (methylcobalamin) does not seem to be effective for treating delayed sleep phase syndrome. Methylcobalamin 0.5-1 mg three times daily, with or without bright light therapy, also does not seem to help people with primary circadian rhythm sleep disorders (1344,1345,1346,1347,1348).
• Cognitive impairment. Oral vitamin B12 does not seem to be beneficial for older adults with cognitive impairment. Details: A meta-analysis of clinical research in elderly adults with mild cognitive impairment or dementia shows that taking vitamin B12, usually with other B vitamins, does not improve cognitive function (50510). One clinical trial in elderly people with memory complaints shows that taking a combination of B vitamins, including folic acid 0.8 mg, vitamin B12 0.5 mg, and vitamin B6 (form not specified) 20 mg daily for 24 months reduces cerebral atrophy in the gray matter regions associated with Alzheimer disease by up to seven-fold when compared with placebo. However, this protection does not occur in patients with the lowest average blood levels of homocysteine (90374).
• Fall prevention. Oral vitamin B12 does not seem to reduce the risk of falls. Details: Clinical research shows that taking B vitamins, including folic acid 400 mcg and vitamin B12 500 mcg, daily for 2 years does not prevent falls when compared with placebo in elderly individuals also taking vitamin D (96148).
• Osteoporosis. Oral vitamin B12 does not seem to reduce the risk of osteoporotic fractures. Details: Clinical research in elderly patients or patients with a history of cerebrovascular disease shows that taking vitamin B12 500 mcg and folic acid 0.4-2 mg, with or without vitamin B6 25 mg, daily for 2-3 years does not seem to reduce the risk for osteoporotic fractures when compared with placebo (90377,90393). A 5-7 year follow-up of this research has also found no benefit (103981).
• Physical performance. Oral vitamin B12 does not seem to improve physical performance in older adults. Details: Clinical research shows that taking B vitamins, including folic acid 400 mcg and vitamin B12 500 mcg, daily for 2 years does not increase hand strength or improve performance such as walking when compared with placebo in elderly individuals also taking vitamin D (96148).

INSUFFICIENT RELIABLE EVIDENCE to RATE

• Age-related macular degeneration (AMD). Oral vitamin B12 has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: A large-scale clinical study shows that taking vitamin B12 1000 mcg, folic acid 2.5 mg, and vitamin B6 50 mg daily, reduces the risk of developing AMD in females over 40 years of age with a history of cardiovascular disease (CVD) or at least three risk factors for CVD. Those who took this combination for an average of 7.3 years had a 34% reduced risk of developing AMD and a 41% reduced risk of visually significant AMD when compared with placebo (14620). It is unclear if this effect is due to vitamin B12, other ingredients, or the combination.
• Amyotrophic lateral sclerosis (ALS, Lou Gehrig's disease). It is unclear if high-dose intramuscular vitamin B12 improves the prognosis of ALS. Details: A clinical study in patients with ALS symptoms for 3 years or less shows that intramuscular vitamin B12 (methylcobalamin) 25-50 mg twice weekly for 3.5 years does not slow functional decline or increase the time until ventilation or death when compared with placebo. However, other clinical research in patients with early-stage ALS shows that intramuscular methylcobalamin 50 mg twice weekly for 16 weeks is associated with slower functional decline and a longer period of time until death or full ventilation when compared with placebo (104947,111556). These effects seem to be particularly notable in fine and gross motor skills, but not bulbar or respiratory functions. Furthermore, vitamin B12 and riluzole slowed clinical progression of ALS more than riluzole alone (111556).
• Angioplasty. Oral vitamin B12 has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: Some evidence suggests that vitamin B12 400 mcg, folic acid 1 mg, and vitamin B6 10 mg daily can decrease the rate of restenosis in patients treated with balloon angioplasty (8009,9412,34540). However, this combination does not seem to be as effective for reducing restenosis in patients after coronary stenting (8009). An intravenous loading dose of folic acid, pyridoxine, and vitamin B12 followed by oral administration of folic acid 1.2 mg, pyridoxine 48 mg, and vitamin B12 60 mcg daily after bare metal coronary stenting also does not seem to reduce restenosis and might actually increase restenosis (12150,12151,34540). Due to the lack of evidence of benefit and potential for harm, this combination of vitamins should not be recommended for patients receiving coronary stents (12151). It is unclear if any effects are due to vitamin B12, other ingredients, or the combination.
• Anxiety. Although there is interest in using oral vitamin B12 for anxiety and panic attacks, there is insufficient reliable information about the clinical effects of vitamin B12 for these uses.
• Asthma. Although there is interest in using oral vitamin B12 for asthma, there is insufficient reliable information about the clinical effects of vitamin B12 for this condition.
• Atherosclerosis. Oral vitamin B12 has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: One small clinical study in patients with intermediate risk for coronary heart disease shows that taking vitamin B12 100 mcg, aged garlic extract 250 mg, folic acid 300 mcg, vitamin B6 12.5 mg, and L-arginine 100 mg daily for 12 months reduces coronary artery calcium progression when compared with placebo (88385). It is unclear if this effect is due to vitamin B12, other ingredients, or the combination.
• Atopic dermatitis (eczema). It is unclear if topical vitamin B12 reduces the severity of eczema. Details: Preliminary clinical research shows that applying a specific topical vitamin B12 0.07% cream (Regividerm) twice daily reduces the extent and severity of atopic dermatitis when compared with placebo (15765).
• Attention. Although there is interest in using oral vitamin B12 for improving attention and focus, there is insufficient reliable information about the clinical effects of vitamin B12 for this use.
• Cancer. It is unclear if oral vitamin B12 reduces overall cancer risk when used in combination with other B vitamins. Details: An ancillary clinical study in middle-aged and elderly adults with cardiovascular disease shows that taking a combination of vitamin B12 (cyanocobalamin) 0.02 mg, folic acid 0.56 mg, and vitamin B6 3 mg, with or without eicosapentaenoic acid (EPA) 400 mg plus docosahexaenoic acid (DHA) 200 mg, for a median of 4.7 years does not reduce the risk of cancer when compared with placebo (90666). An additional secondary analysis of clinical research in patients recovering from stroke or transient ischemic attack shows that taking vitamin B12 500 mcg, folic acid 2 mg, and vitamin B6 25 mg daily for around 3.4 years does not reduce the risk of cancer when compared with placebo (90378). The validity of these findings is limited because the studies were not designed nor adequately powered to test for cancer risk.
• Cardiovascular disease (CVD). Oral vitamin B12, taken along with other B vitamins, does not seem to improve secondary prevention of death or myocardial infarction in patients with CVD. However, it might slightly reduce the risk of stroke. Details: Overall evidence from clinical research and meta-analyses shows that taking vitamin B12 in combination with folic acid and/or vitamin B6 does not seem to reduce the risk for secondary death or myocardial infarction in patients with or at risk for CVD (11387,13482,34540,50423,83050,90379,97619). In fact, some research suggests that long-term supplementation with vitamin B6, folic acid, and vitamin B12 for secondary prevention increases the risk of CVD by 20% despite lowering homocysteine levels by 30% (13482). However, other research shows that taking vitamin B12 in combination with other B vitamins modestly reduces the risk of stroke, although results are conflicting (11387,13482,50423,83050,96150,96165,97619,107136). It is unclear which specific combination of B vitamins, if any, might be optimal for reducing stroke risk and which patients are most likely to benefit. In 2001, prior to the publication of the highest quality research on this topic, the US Food and Drug Administration (FDA) approved a qualified health claim stating that, as part of a well-balanced diet that is low in saturated fat and cholesterol, folic acid, vitamin B6, and vitamin B12 may reduce the risk of vascular disease (102368).
• Cervical cancer. It is unclear if oral vitamin B12 reduces cervical cancer risk. Details: Some epidemiological evidence has found that increasing vitamin B12 intake from dietary and supplement sources, along with folic acid, thiamine, and riboflavin, might decrease the risk of precancerous cervical lesions (11074). Also, an analysis of two case control studies has found that increased intake of vitamin B12 is associated with a 75% reduced odds of cervical cancer (34609).
• Chemotherapy-induced peripheral neuropathy. Oral vitamin B12 has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: Preliminary clinical research in patients receiving chemotherapy shows that a combination of B vitamins that includes vitamin B12 (cyanocobalamin) 1000 mcg, taken daily starting one week prior to treatment and finishing 12 weeks after treatment is completed, does not prevent peripheral neuropathy when compared with placebo (96173).
• Child development. It is unclear if oral vitamin B12 is beneficial for child development. Details: Population research has found that daily dietary intake of less than 2.26 mcg vitamin B12 in the third trimester of pregnancy is associated with an increased risk of poorer outcomes in the offspring for some measures of speech and mathematics ability, including vocabulary at 24 months, combining words at 38 months, speech intelligibility at 6 years, and math comprehension between ages 8-11 years, when compared with dietary intakes of at least 2.26 mcg daily. There was no association between prenatal vitamin B12 intake and reading or spelling abilities, vocabulary at other ages, or full-scale Intelligence Quotient (IQ) at ages 8 or 15 (107143). Furthermore, a very large clinical study in infants of pregnant adults, 71% of whom were deficient in vitamin B12 at baseline, shows that taking vitamin B12 50 mcg daily starting in early pregnancy (<15 weeks gestation) until 6 months postpartum does not improve neurodevelopment as measured by language, motor, socioemotional, or cognitive scores at 12 months old and may worsen early motor performance at 8-12 weeks when compared with placebo. However, the negative effects on motor performance resolved by 6 and 12 months of age (112431).
• Child growth. Oral vitamin B12 taken by pregnant adults does not seem to be beneficial for infant growth. Details: A very large clinical study in infants of pregnant adults, 71% of whom were deficient in vitamin B12 at baseline, shows that taking vitamin B12 50 mcg daily starting in early pregnancy (<15 weeks gestation) until 6 months postpartum does not improve the infant's linear growth, length, or weight at 12 months of age (112431).
• Chronic obstructive pulmonary disease (COPD). It is unclear if oral vitamin B12 reduces the risk of COPD. Details: Clinical research in patients with COPD shows that taking vitamin B12 500 mg daily for 8 weeks modestly improves endurance on the cycle ergometer, but does not improve oxygen consumption, when compared with placebo (96172).
• Cognitive function. Oral vitamin B12 has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: A moderate-sized clinical study in healthy, middle-aged adults shows that taking a combination product containing vitamin B12, other B vitamins, bacopa, and gingko biloba twice daily for 12 weeks does not improve measures of memory, attention, cognition, mood, or stress reactivity when compared with placebo (111334).
• Colorectal cancer. It is unclear if oral vitamin B12 reduces colorectal cancer risk. Details: Some epidemiological evidence has found that increased dietary intake of vitamin B12 is associated with a reduced risk of developing colorectal cancer (90383). However, preliminary clinical research shows that taking vitamin B12 1 mg, folic acid 2.5 mg, and vitamin B6 50 mg daily for up to 7.3 years does not reduce the risk of colorectal adenoma in females at high risk for cardiovascular disease (90389). Furthermore, a secondary analysis of clinical research in elderly patients suggests that taking vitamin B12 500 mcg and folic acid 400 mcg daily for 2 years might increase the risk of colorectal cancer when compared with placebo (90393).
• Coronavirus disease 2019 (COVID-19). It is unclear if oral vitamin B12 is beneficial for patients with COVID-19. Details: A small observational study in hospitalized patients with COVID-19 pneumonia has found that higher plasma vitamin B12 levels may be associated with an increased risk of transfer to intensive care or death than lower plasma levels. However, when multivariate regression was conducted, only patient age was associated with worsened outcomes. Additionally, the total study population was small, with only nine of 49 patients experiencing the worsened outcomes (107138).
• Dementia. It is unclear if oral vitamin B12 reduces the risk of developing dementia. Details: A large cohort of Danish adults has found that vitamin B12 levels or intake does not seem to impact the risk of developing Alzheimer disease or other dementias (104922). However, vitamin B12 might be beneficial in specific patient populations. A small observational study in patients with Parkinson disease has found that higher vitamin B12 levels (648.5 ng/L) are associated with a lower risk of developing dementia when compared with lower vitamin B12 levels (452 ng/L) (103975). It is not yet known if supplementation with vitamin B12 reduces the risk for dementia in these patients.
• Depression. It is unclear if oral vitamin B12 is beneficial for reducing depression risk. Details: A meta-analysis of epidemiological research has found that the highest dietary intake of vitamin B12 is associated with a 14% reduced risk of depression. However, in a sub-analysis, this association was not significant in males (107133). In contrast, one epidemiological study in older males included in the analysis has found that daily dietary intake of at least 4.79 mcg vitamin B12 is linked with a 58% lower risk of depression when compared with daily intake of less than 3.16 mcg. In this study, this inverse association was not observed in females (96168). Other observational research has found that low-normal serum vitamin B12 levels are associated with a 3.8 times increased risk for depression during pregnancy when compared with normal vitamin B12 levels (102384). It is unclear if increased intake of vitamin B12 through the diet or supplements reduces the risk for depression or is beneficial for treating symptoms of depression in any population. However, a meta-analysis of clinical research in elderly populations shows that supplementation with vitamin B12 100-1000 mcg daily, usually in combination with folic acid 400-2000 mcg daily, does not reduce symptoms of depression. Most individuals in these studies were not specifically diagnosed with depression (107140).
• Diabetes. It is unclear if oral vitamin B12 improves glycemic indices or prevents loss of skeletal muscle in patients with diabetes. Details: A small clinical study in patients with diabetes in India who are stabilized on metformin and/or a sulfonylurea shows that taking vitamin B12 (methylcobalamin) 500 mcg with or without folic acid 5 mg daily for 8 weeks seems to reduce glycated hemoglobin (HbA1C) by 1.3% to 1.5%, compared with a 0.3% increase with placebo (104917). This study is limited due its small sample size and lack of blinding. In elderly adults with type 2 diabetes, population research has found a lower dietary intake of vitamin B12 (average of 11.2 mcg daily) in individuals with a loss of skeletal muscle mass of at least 1.2%, compared with an average intake of 13.4 mcg daily in those with a skeletal muscle mass loss of less than 1.2%. However, further analysis determined that any relationship between vitamin B12 intake and loss of skeletal muscle mass was only significant in individuals with insufficient energy intake overall (107151).
• Diabetic neuropathy. Small clinical studies suggest that oral vitamin B12 may modestly improve pain in patients with diabetic neuropathy. Details: Two small clinical studies in patients with diabetic peripheral neuropathy show that taking vitamin B12 (methylcobalamin) 1-1.5 mg for 4-12 months modestly improves pain when compared with baseline or placebo (82841,104923). Some research also shows that vitamin B12 may be beneficial in combination with other ingredients. Studies have evaluated products containing vitamin B12 (methylcobalamin or cyanocobalamin), benfotiamine, and vitamin B6 daily for 9-12 weeks (82931,82939); and vitamin B12 (methylcobalamin) 2 mg, folic acid (L-methylfolate) 3 mg, and vitamin B6 (pyridoxal-5'-phosphate) 35 mg (Metanx; Pamlab) daily for 24 weeks (90375).
• Diarrhea. It is unclear if oral vitamin B12 is beneficial for reducing diarrhea in children. Details: Preliminary clinical research in children aged 6-30 months from low- and middle-income countries shows that taking vitamin B12 at twice the recommended dietary allowance, with or without folic acid, does not reduce the risk for diarrhea when compared with placebo (90391).
• Fatigue. It is unclear if intramuscular vitamin B12 is beneficial for improving well-being in those with fatigue or tiredness. Details: A small crossover trial in patients complaining of tiredness or fatigue shows that receiving intramuscular injections of vitamin B12 (hydroxocobalamin) 5 mg twice weekly for 2 weeks seems to improve general well-being and happiness, and has a trend toward improving fatigue, when compared with placebo (10127). The validity of this study is limited by a large drop-out rate and unstandardized outcome measures.
• Hearing loss. Oral vitamin B12 has only been evaluated in combination with adenosine triphosphate; its effect when used alone is unclear. Details: A small observational study in adults with idiopathic sudden sensorineural hearing loss has found that taking vitamin B12 1.5 mg with adenosine triphosphate 300 mg daily for 8-16 weeks is associated with modestly reduced hearing loss at 4-6 months after starting treatment when compared with taking the combination for less than 8 weeks (104924). This finding is limited due to its observational nature and lack of a control group.
• Hepatitis C. It is unclear if intramuscular vitamin B12 is beneficial for sustaining viral response in patients with chronic hepatitis C infection. Details: A small clinical study in patients with chronic hepatitis C infection shows that intramuscular vitamin B12 (cyanocobalamin) 5000 mcg every 4 weeks along with standard care improves sustained viral response when compared with standard of care alone (90386).
• Hypertriglyceridemia. It is unclear if oral vitamin B12 is beneficial for reducing triglyceride levels. Details: Some evidence shows that taking vitamin B12 7.5 mcg with fish oil 5 grams might be superior to fish oil alone when used daily to reduce total serum cholesterol and triglycerides. This suggests vitamin B12 might have an independent effect in lowering serum cholesterol and triglycerides, but further investigation is needed to confirm this effect (8694).
• Hypotension. It is unclear if oral vitamin B12 is beneficial for treating hypotension. Details: A meta-analysis of 3 observational studies in patients hospitalized with hypotension secondary to cardiac surgery vasoplegia suggests that administration of intravenous vitamin B12 (hydroxocobalamin) is associated with an 8 mmHg higher mean arterial pressure (MAP) at 1 hour but no change in vasopressor dosage at 1 hour or mortality rate when compared with methylene blue (112264). The validity of these findings is limited by the inclusion of only retrospective studies.
• Infant development. It is unclear if taking oral vitamin B12 during pregnancy is beneficial for improving infant development. Giving oral vitamin B12 to infants does not seem to be beneficial. Details: Clinical research shows that supplementation with vitamin B12 50 mcg daily from less than 14 weeks gestation until 6 weeks postpartum does not improve cognitive development in infants by 9 months of age when compared with placebo (96174). When these children were evaluated at 30 months of age, a very small benefit of vitamin B12 on expressive language was identified; however, there was no effect on cognition, receptive language, fine motor skills, or gross motor skills (100169). It is unknown whether a longer duration of postpartum supplementation or supplementation in specific populations might be beneficial. Vitamin B12 supplementation in infants has also been evaluated. A large clinical trial in marginally stunted Nepalese infants aged 6-11 months shows that giving vitamin B12 (cyanocobalamin) 2 mcg daily for 12 months reduces homocysteine levels, but does not improve motor or cognitive development, when compared with placebo (104926).
• Inflammatory bowel disease (IBD). Although there is interest in using oral vitamin B12 for IBD, there is insufficient reliable information about the clinical effects of vitamin B12 for this condition.
• Lung cancer. Oral vitamin B12 has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: The association between vitamin B12 and lung cancer is unclear. Some population research found no relationship between blood levels of vitamin B12 and lung cancer (9454). However, other observational research involving over 5,000 case-control pairs found that higher vitamin B12 levels are linked with an increased risk for lung cancer (102383). It is unclear if increased intake of vitamin B12, either through the diet or supplementation, directly affects the risk of lung cancer.
• Male infertility. Oral vitamin B12 has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: A retrospective study in adult males with idiopathic and varicocele-related infertility suggests that taking a combination product containing vitamin B12 1.5 mcg, L-carnitine, acetyl L-carnitine, citric acid, selenium, coenzyme Q10, vitamin C, zinc, and folic acid (Proxeed Plus) twice daily for 6 months is associated with improvements in ejaculate volume, sperm count, sperm concentration, total motility, and progressive motility in patients with idiopathic infertility when compared to baseline. However, improvement in sperm morphology was lacking. Furthermore, patients with more severe varicocele seem to benefit most, especially with regard to progressive motility (111296). The validity of these findings is limited by a lack of comparator group. Further, it is unclear if these effects are due to vitamin B12, other ingredients, or the combination.
• Mastalgia. Oral vitamin B12 has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: A small clinical trial in patients with mastalgia shows that taking a combination of vitamin B12 as methylcobalamin 100 mg, gamma-linolenic acid, and vitamin C daily for 12 weeks does not improve the proportion of patients with minimal or no pain when compared with placebo (111059).
• Multiple sclerosis (MS). Although there is interest in using oral vitamin B12 for MS, there is insufficient reliable information about the clinical effects of vitamin B12 for this condition.
• Nonalcoholic fatty liver disease (NAFLD). It is unclear if oral vitamin B12 is beneficial for NAFLD. Details: A small clinical study in adults with NAFLD shows that taking vitamin B12 1000 mcg daily for 12 weeks reduces serum levels of homocysteine but has no effect on serum aminotransferases, measures of steatosis, fibrosis scores, fasting blood glucose, serum insulin, measures of insulin resistance, triglycerides, low-density lipoprotein (LDL) cholesterol, or high-density lipoprotein (HDL) cholesterol when compared with placebo (111555).
• Pancreatic cancer. It is unclear if oral vitamin B12 is beneficial for reducing the risk of pancreatic cancer. Details: Most population research has found that increased intake of vitamin B12, as a supplement or in the diet, is not associated with a reduced risk of pancreatic cancer (9327,104927). However, a small, retrospective population study in which smoking and non-smoking adults recalled past eating habits found that increased dietary intake of vitamin B12 is associated with a 33% reduction in pancreatic cancer risk (97976). These conflicting findings may be related to study methodology, as well as the age, gender, or smoking status of the included patients.
• Periodontitis. Although there is interest in using oral vitamin B12 for periodontitis, there is insufficient reliable information about the clinical effects of vitamin B12 for this condition.
• Peripheral neuropathy. Oral vitamin B12 has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: Preliminary clinical research shows that taking a specific product containing vitamin B12 3 mcg, folic acid 400 mcg, and uridine monophosphate 50 mg (Keltican) daily for 60 days reduces pain by 44% and decreases analgesic use by over 75% when compared to baseline in patients with peripheral neuropathy, including those with lumbar/lumbosacral radiculopathy, sciatic pain, and cervical radiculopathy (90384). The validity of this finding is limited by the lack of a control group. Furthermore, it is unclear if the benefits are due to vitamin B12, other ingredients, or the combination.
• Psoriasis. Topical vitamin B12 has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: Preliminary clinical research shows that a specific cream containing vitamin B12 and avocado oil (Regividerm, Regeneratio Pharma AG) reduces symptoms of psoriasis as effectively as calcipotriol ointment (Psorcutan) after 12 weeks of therapy. The vitamin B12 combination cream also causes less irritation than calcipotriol (14909). It is unclear if the benefits are due to vitamin B12, other ingredients, or the combination.
• Respiratory tract infections. A small study suggests that oral vitamin B12 does not reduce the rate of respiratory tract infections in children. Details: Preliminary clinical research in children aged 6-30 months from low-and middle-income countries suggests that taking vitamin B12 at twice the recommended dietary allowance with or without folic acid does not reduce the risk for lower respiratory tract infections when compared with placebo (90391).
• Schizophrenia. Oral vitamin B12 has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: Clinical research shows that taking a combination of vitamin B12 400 mcg and folic acid 2 mg daily for 16 weeks improves negative symptoms when compared with placebo in patients with schizophrenia who have persistent symptoms and a specific genetic variant of the folate transporter gene FOLHI. This variant normally results in reduced folate absorption. However, in patients without this genetic variant, folate is not beneficial with respect to negative symptom improvement (90387).
• Sickle cell disease. Oral vitamin B12 has only been evaluated in combination with other B vitamins; its effect when used alone is unclear. Details: Preliminary clinical research in adults with sickle cell disease shows that taking vitamin B12 4.2-6 mcg, folic acid 700 mcg, and vitamin B6 4.2-6 mg daily might lower homocysteine levels. However, it is unknown if this will reduce the risk of endothelial damage in these patients (9324).
• Stroke. It is unclear if oral vitamin B12, either alone or with other B vitamins, is beneficial for stroke prevention. Details: Epidemiological research has found that people with a higher intake of vitamin B12 from dietary sources do not have a reduced risk of ischemic or hemorrhagic stroke (14316). A number of clinical studies and meta-analyses show that supplementation with folic acid, vitamin B6, and vitamin B12, alone or in combination, does not reduce the risk of stroke in patients with cardiovascular disease (CVD) or impaired kidney function (11387,13482,50420,50423,83050,90379,90380,96150). However, a more recent meta-analysis of 10 clinical trials including over 44,000 patients shows that B vitamin supplementation modestly reduces the relative risk of stroke by 10% when compared with placebo in patients at risk or with a history of CVD (97619). This meta-analysis differed from some of the earlier analyses due to the inclusion of several additional clinical trials. Also, a meta-analysis in adults with a history of stroke shows that B vitamin supplementation modestly reduces the relative risk of stroke recurrence by 13% and vascular death by 11% when compared with placebo (107136). In 2001, prior to the publication of the highest quality research on this topic, the US Food and Drug Administration (FDA) allowed a qualified health claim stating that, as part of a well-balanced diet that is low in saturated fat and cholesterol, folic acid, vitamin B6, and vitamin B12 may reduce the risk of vascular disease (102368). Unfortunately, even after the publication of higher quality research, it is still unclear which specific combination of B vitamins is optimal and which patients are most likely to benefit. One network meta-analysis suggests that a combination of folic acid and vitamin B6 lowers the risk of stroke more effectively than B vitamin mixtures that include vitamin B12 (96165). However, this analysis is limited because it didn't account for dosing. Another meta-analysis suggests that exposure to low, but not high, amounts of vitamin B12 (cyanocobalamin) seems to reduce stroke risk (96150).
• Tinnitus. It is unclear if intramuscular vitamin B12 is beneficial in patients with tinnitus. Details: A small clinical study shows that intramuscular vitamin B12 2500 mcg weekly for 6 weeks reduces tinnitus severity by 22% when compared to baseline in patients with chronic tinnitus and vitamin B12 deficiency, but not in patients with normal levels of vitamin B12. Vitamin B12 does not improve pitch or volume in either group of patients (96170). The validity of this finding is limited by the lack of a control group.
• Venous thromboembolism (VTE). It is unclear if oral vitamin B12 is beneficial for preventing VTE. Details: Epidemiological research has found that low levels of vitamin B12 are associated with an increased risk for VTE. However, clinical trials evaluating the use of B vitamins for prevention of VTE have shown conflicting results (90398). More evidence is needed to rate vitamin B12 for these uses.

(Read more about VITAMIN B12)

EFFECTIVE

• Pyridoxine-dependent epilepsy. Intravenous vitamin B6 is effective for controlling pyridoxine-dependent seizures. Details: Pyridoxine-dependent seizures are a rare type of refractory seizures in neonates that do not respond to anticonvulsant drugs. These seizures are typically controlled within minutes of intravenous administration of pyridoxine, a form of vitamin B6. Pyridoxine-dependent seizures can be due to genetic (autosomal recessive) pyridoxine dependency, or more commonly, a result of the use of high-dose pyridoxine during pregnancy (8197,8198).
• Sideroblastic anemia. Oral vitamin B6 is effective for treating hereditary sideroblastic anemia. Details: Taking vitamin B6 (pyridoxine) orally is effective for treating hereditary sideroblastic anemia (15,9518). Taking the active form of vitamin B6 (pyridoxal-5'-phosphate) also seems to be effective in cases in which the patient does not respond to pyridoxine (93049).
• Vitamin B6 deficiency. Oral vitamin B6 is effective for preventing and treating vitamin B6 deficiency. Details: Taking oral vitamin B6 can prevent and treat vitamin B6 deficiency (15).

LIKELY EFFECTIVE

• Hyperhomocysteinemia. Taking vitamin B6 orally, alone or in combination with folic acid, is effective for reducing hyperhomocysteinemia. Details: Vitamin B6 (pyridoxine) seems to lower homocysteine concentrations when folic acid and vitamin B12 are at physiologic levels or when given with folic acid and vitamin B12 supplements (9451,83042,107136). A combination of vitamin B6 100 mg and folic acid 0.5 mg daily seems to lower homocysteine levels by about 35% and is recommended for people with postprandial hyperhomocysteinemia (1489,9406). Other research shows that taking pyridoxine 50-200 mg daily reduces postprandial homocysteine levels by 32% to 35% (9406,10350). Pyridoxine also seems to reduce homocysteine levels in patients with kidney failure, kidney transplant patients (1489,6884,9414,9415), or patients who receive general anesthesia with nitrous oxide (9481). However, some research in healthy adults suggests that adding pyridoxine to folic acid might not provide any additional benefit over folic acid alone (9400,9405,9409,50145). Hyperhomocysteinemia is considered by some to be an independent risk factor for atherosclerosis, recurrent thromboembolism, deep vein thrombosis, myocardial infarction, and ischemic stroke (1899,3323,9402,9405,9408,9409). However, elevated homocysteine levels may be a marker, as opposed to a cause, of vascular disease (11387,11388). A 5 µmol/L increase in plasma homocysteine increases the risk of cerebrovascular disease by 50% and the odds of coronary heart disease by 60% and 80% in males and females, respectively (9407,9411). However, it is not clear if reducing homocysteine levels results in reduced cardiovascular morbidity and mortality (1489,6883,6884,9308,9400,9405,9409). Folic acid, vitamin B6, and vitamin B12 supplementation can reduce total homocysteine from 13.4 to 11 µmol/L. However, this reduction does not seem to help with secondary prevention of death or myocardial infarction, and some research even suggests an increase in cardiovascular disease (CVD) risk (11387,13482,50423,83050,97619). There is also debate about whether supplementation with homocysteine-lowering B vitamins can reduce the risk of stroke. A number of large clinical studies and meta-analyses show that supplementation with folic acid, vitamin B6, and vitamin B12, alone or in combination, does not reduce the risk of stroke in patients with CVD or impaired renal function (11387,13482,50423,83050,96150). However, a more recent meta-analysis shows that B vitamin supplementation modestly reduces the relative risk of stroke by 10% when compared with placebo in patients at risk for or with a history of CVD (97619). Also, a meta-analysis in patients with a history of stroke shows that B vitamin supplementation modestly reduces the relative risk of stroke recurrence by 13% and the risk of vascular death by 11% when compared with placebo (107136).

POSSIBLY EFFECTIVE

• Antipsychotic-induced hyperprolactinemia. It is unclear if oral vitamin B6 is beneficial for patients with antipsychotic-induced hyperprolactinemia. Details: Clinical research in male patients with hyperprolactinemia who are on a consistent antipsychotic dose shows that taking vitamin B6 300 mg twice daily for 16 weeks reduces serum prolactin levels by 68%, compared with 37% in patients taking aripiprazole 5 mg twice daily. Also, 67% of patients taking vitamin B6 had prolactin levels less than 40 mcg/mL versus 2% of those taking aripiprazole (107128).
• Kidney stones (nephrolithiasis). Oral vitamin B6 seems to decrease urinary oxalate levels and decrease the risk of kidney stone formation in some patients. Details: There is some evidence that taking vitamin B6 (pyridoxine) orally, alone or in combination with magnesium, can decrease urinary oxalate levels in people with type I primary hyperoxaluria, a hereditary disorder (1201,6437,6438,6439,6440,8548,8549,8550). Additionally, a small clinical study in this population suggests that intravenous pyridoxine hydrochloride can reduce urinary oxalate by 25.5% when compared to baseline (90796). In patients with idiopathic hyperoxaluria, taking a combination of pyridoxine 25mg and magnesium oxide 400 mg for 3 months decreases urinary oxalate by approximately 16%, with 68% of patients experiencing a reduction. However, supplementation is less effective than following a low-oxalate diet, which reduces urinary oxalate in 91% of patients by an average of 31% (107127). There is also preliminary evidence that higher pyridoxine intake in females with no history of kidney stones is associated with decreased risk of kidney stone formation (6441), but this association has not been found in males (6442).
• Pregnancy-induced nausea and vomiting. Oral vitamin B6 may reduce nausea and vomiting in some pregnant patients and is sometimes used in combination with doxylamine. Details: While some conflicting evidence exists, most small clinical studies suggest that oral vitamin B6 is effective for improving nausea and vomiting associated with pregnancy when compared with baseline or placebo. However, vitamin B6 may not be as effective as ginger (110459). Two small clinical studies show that taking vitamin B6 (pyridoxine) 25 mg every 8 hours for 3-4 days decreases pregnancy-induced nausea severity and vomiting incidence when compared with placebo (6168,16306). A larger clinical trial shows that taking lower doses of vitamin B6, 10 mg every 8 hours over 5 days, improves pregnancy-induced nausea, but not vomiting, when compared with placebo (6167). A small clinical study in patients with mild to moderate nausea and vomiting shows that taking a higher dose of 40 mg twice daily for 4 days is more effective than placebo, but no better than ginger 500 mg twice daily (99404). The American College of Obstetrics and Gynecology (ACOG) considers vitamin B6 at a dose of 10-25 mg 3 to 4 times daily a first-line treatment for pregnancy-induced nausea and vomiting due to its benign safety profile (111601). However, it is not effective for all patients, such as those with hyperemesis gravidarum, a severe form of pregnancy-induced nausea and vomiting. Adding vitamin B6 20 mg three times daily for 2 weeks to intravenous rehydration, metoclopramide, and thiamine seems to be no more effective than placebo for reducing vomiting in hyperemesis gravidarum (99405). Vitamin B6 is also sometimes used in combination with doxylamine. In fact, a combination of vitamin B6 plus doxylamine (Diclegis or Bonjesta, Duchesnay Inc., and various generics) has been approved by the US Food and Drug Administration (FDA) as a prescription product111601). ACOG recommends vitamin B6 in combination with doxylamine as another first-line treatment option (111601). However, the clinical trial used to obtain FDA approval has some methodological problems, and the significance of the results has been questioned. The improvement in symptom scores seen with Diclegis was less than one point on a 13-point scale, which is unlikely to be clinically significant (97998). Also, some clinical research shows that taking pyridoxine 25 mg and doxylamine 12.5 mg is less effective than ondansetron 4 mg when taken every 8 hours for 5 days. Only 41% of the patients using pyridoxine and doxylamine had a clinically significant reduction in nausea, compared to 92% of patients using ondansetron (90797). The combination of vitamin B6 and doxylamine is also studied with acupuncture. A large clinical study in patients with moderate to severe pregnancy-induced nausea and vomiting conducted in China shows that taking vitamin B6-doxylamine (Diclegis, Duchesnay, Inc) 20 to 40 mg each at bedtime for 14 days in combination with daily acupuncture modestly improves patient-reported nausea and vomiting scores when compared with either intervention alone (111820). However, it is unclear whether this improvement is clinically significant.
• Premenstrual syndrome (PMS). Oral vitamin B6 seems to reduce PMS symptoms. Details: There is some evidence that taking vitamin B6 (pyridoxine) orally can improve symptoms of PMS such as breast pain or tenderness (mastalgia) and depression in some patients. Pyridoxine in doses of at least 50 mg daily, plus magnesium oxide 200 mg daily, seems to relieve PMS-related anxiety and other symptoms (8555,39007,82962). Although some clinicians advocate doses of pyridoxine 200-500 mg daily for PMS, doses of 50-100 mg daily seem to work just as well. There is no apparent dose-response curve for PMS, so the lowest effective dose should be used. Higher doses might increase the risk of side effects (3093).

POSSIBLY INEFFECTIVE

• Age-related cognitive decline. Oral vitamin B6 does not seem to slow age-related cognitive decline. Details: One clinical trial in elderly people with memory complaints shows that taking a combination of B vitamins, including folic acid 0.8 mg, vitamin B12 0.5 mg, and vitamin B6 (form not specified) 20 mg daily for 24 months reduces cerebral atrophy in the gray matter regions associated with Alzheimer disease by up to seven-fold when compared with placebo. However, this protection does not occur in patients with the lowest average blood levels of homocysteine (90374). Furthermore, other clinical research shows that taking vitamin B6 (pyridoxine) 3-75 mg daily in combination with folic acid and vitamin B12 does not improve cognitive function in elderly adults (14392,50225,50510).
• Alzheimer disease. Oral vitamin B6 does not seem to improve cognitive function in patients with Alzheimer disease when used in combination with other B vitamins. Also, oral vitamin B6 does not seem to reduce the risk of developing this condition. Details: Clinical research in patients with probable Alzheimer disease taking routine medications shows that taking vitamin B6 25 mg with folic acid 5 mg and vitamin B12 1 mg daily for 18 months does not have a beneficial effect on cognitive function or the severity of disease when compared with placebo. In this study, all patients were consuming a folate-fortified diet (50319). Also, population research in elderly adults has found that a high intake of vitamin B6 from dietary or supplemental sources is not associated with a decreased risk of Alzheimer disease when compared to lower vitamin B6 intake (13165,15270).
• Carpal tunnel syndrome. Oral vitamin B6 does not seem to reduce symptoms of carpal tunnel syndrome. Details: Most research shows that people with carpal tunnel syndrome are not generally deficient in vitamin B6 and do not benefit from taking vitamin B6 supplements (8203,8937,9448,9450,9478,9482). Although early studies by a single group of researchers, as well as anecdotal reports, suggest that taking vitamin B6 may relieve carpal tunnel symptoms, more reliable research has not supported these findings (8202,9445,9447,9449,9483,15955,83086).
• Cataracts. Oral vitamin B6 does not seem to slow cataract development. Details: Clinical research in females with existing cardiovascular disease (CVD) or at increased risk of CVD shows that taking a combination of folic acid 2.5 mg, vitamin B6 (form not specified) 50 mg, and vitamin B12 1 mg daily for an average of 7.3 years does not reduce the risk of cataracts when compared with placebo. Furthermore, the risk of cataract extraction was increased by 28% (96149).
• Chemotherapy-induced acral erythema. While some conflicting evidence exists, most research suggests that oral or topical vitamin B6 does not seem to prevent or reduce the severity of acral erythema induced by chemotherapy. Details: A meta-analysis of 10 clinical trials and 4 observational studies shows that taking vitamin B6 60-500 mg daily for up to 8 chemotherapy cycles does not prevent chemotherapy-induced acral erythema or reduce the incidence of severe cases when compared with control. Most studies used capecitabine chemotherapy alone or in combination, and one study used pegylated liposomal doxorubicin; however, no subgroup analysis was conducted to differentiate chemotherapy regimens. Results did not seem to vary based on study location, study design, or vitamin B6 dose (104930). However, a more recent preliminary clinical study in patients receiving doxorubicin for multiple myeloma shows that taking vitamin B6 100 mg on the first day of chemotherapy then twice daily for 7 days with each cycle reduces the risk of developing acral erythema by 72%, but does not improve the severity of acral erythema, when compared with no vitamin B6 supplementation (110458). Also, one small, low-quality clinical study suggests that taking vitamin B6 400 mg daily reduces the risk of moderate or severe chemotherapy-induced acral erythema when compared with vitamin B6 200 mg daily; however, the higher dose also seems to be associated with worsened tumor response and increased treatment failure (97620). Topical vitamin B6 has also failed to show benefit. A small clinical study in patients with acral erythema from capecitabine or pegylated liposomal doxorubicin shows that applying vitamin B6 1% cream to affected areas three times daily for 6 weeks does not improve symptoms when compared with placebo (104929).
• Colorectal adenoma. Oral vitamin B6 does not seem to reduce the risk of developing colorectal adenomas. Details: Clinical research shows that taking a combination of B vitamins, including folic acid 2.5 mg, vitamin B6 (pyridoxine) 50 mg, and vitamin B12 1 mg, daily for up to 9.2 years does not reduce the risk of colorectal adenoma in females at high risk of cardiovascular disease when compared with placebo (90389).
• Eclampsia. Oral or intramuscular vitamin B6 does not seem to reduce the risk of eclampsia. Details: Meta-analyses of limited clinical research in pregnant patients show that taking vitamin B6 (pyridoxine), either as 25 mg daily or a single dose of 100 mg orally or intramuscularly, does not reduce the risk of eclampsia when compared with control (83046,96166).
• Osteoporosis. Oral vitamin B6 does not seem to reduce the risk of osteoporotic fractures. Details: Clinical research in patients with cerebrovascular disease shows that taking a combination of B vitamins, including folic acid 2 mg, vitamin B6 (form not specified) 25 mg, and vitamin B12 500 mcg daily for up to 10.5 years does not prevent osteoporotic fractures when compared with placebo (90377). Furthermore, a secondary analysis of two large studies in patients with cardiovascular disease has found that taking vitamin B6 (pyridoxine) 40 mg daily in addition to folic acid and vitamin B12 for 1-3 years is associated with a 42% increased risk of hip fracture over an 11-year period when compared with only folic acid and vitamin B12 (96163). This finding is limited because these studies were not designed to assess the effects of vitamin B6 on fracture risk and the analyses were not adjusted for baseline bone health or fall risk.
• Pre-eclampsia. Oral or intramuscular vitamin B6 does not seem to reduce the risk of pre-eclampsia. Details: Meta-analyses of limited clinical research in pregnant patients show that taking vitamin B6 (pyridoxine), either as 25 mg daily or a single dose of 100 mg orally or intramuscularly, does not reduce the risk of pre-eclampsia when compared with placebo (83046,96166).
• Preterm labor. Oral or intramuscular vitamin B6 does not seem to reduce the risk of preterm labor. Details: Meta-analyses of limited clinical research in pregnant patients shows that taking vitamin B6 (pyridoxine), either as 25 mg daily or a single dose of 100 mg orally or intramuscularly, does not reduce the risk of preterm labor when compared with placebo (83046,96166).

INSUFFICIENT RELIABLE EVIDENCE to RATE

• Acne. Oral vitamin B6 has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: Preliminary clinical research in adults and children with inflammatory acne shows that taking 1-4 tablets of a specific product (NicAzel, Elorac Inc.) containing vitamin B6 (pyridoxine), nicotinamide, azelaic acid, zinc, copper, and folic acid for 8 weeks reduces inflammatory lesions and improves appearance in 88% and 81% of patients, respectively, when compared to baseline (90800). The validity of these findings is limited by the lack of a comparator group.
• Age-related macular degeneration (AMD). Oral vitamin B6 has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: A large-scale clinical study shows that taking vitamin B6 (pyridoxine) 50 mg, vitamin B12 1000 mcg, and folic acid 2.5 mg daily reduces the risk for AMD in females over 40 years of age with a history of cardiovascular disease (CVD) or with risk factors for CVD. Those who took this combination for an average of 7.3 years had a 34% reduced risk of developing AMD and a 41% reduced risk of visually significant AMD when compared with placebo (14620). It is unclear if this effect is due to vitamin B6, other ingredients, or the combination.
• Angioplasty. Oral vitamin B6 has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: Some evidence suggests that vitamin B6 (pyridoxine) 10 mg, folic acid 1 mg, and vitamin B12 400 mcg daily can decrease the rate of restenosis in patients treated with balloon angioplasty (8009,9412). However, this combination does not seem to be as effective for reducing restenosis in patients after coronary stenting (8009). An intravenous loading dose of folic acid, vitamin B6 (pyridoxine), and vitamin B12 followed by oral administration of folic acid 1.2 mcg, vitamin B6 (pyridoxine) 48 mg, and vitamin B12 60 mcg daily after bare metal coronary stenting also does not seem to reduce restenosis and might actually increase restenosis (12150,12151). Due to the lack of evidence of benefit and potential for harm, this combination of vitamins should not be recommended for patients receiving coronary stents (12151). It is unclear if any effects are due to vitamin B6, other ingredients, or the combination.
• Antipsychotic-induced metabolic side effects. It is unclear if oral vitamin B6, as an adjunct to progesterone, is beneficial in patients with antipsychotic-induced amenorrhea. Details: A small clinical study in females with antipsychotic-induced amenorrhea shows that taking vitamin B6 80 mg three times daily for 1 month plus intramuscular progesterone daily for 5 days increases levels of estradiol and follicle stimulating hormone, reduces prolactin levels, and increases the rate of clinical efficacy, defined as the normalization of menstruation and improvement in endocrine indicators, by 14% when compared with progesterone alone (110457).
• Anxiety. It is unclear if oral vitamin B6 is beneficial in patients with anxiety. Details: Clinical research in college students shows that taking vitamin B6 100 mg daily for one month does not reduce anxiety scores when compared with placebo (110453). However, because a diagnosis of anxiety was not a requirement for study participation, it is unclear if these findings can be generalized to patients diagnosed with anxiety.
• Asthma. It is unclear if oral vitamin B6 is beneficial in patients with asthma. Details: Preliminary clinical studies show that taking vitamin B6 (pyridoxine) 200-300 mg daily may improve symptoms of asthma in some patients, but not others, when compared with placebo (7064,7065). Studies have yielded conflicting results, with some research suggesting that it may only be beneficial in children with severe asthma (7065). Additionally, some research suggests that theophylline may lower vitamin B6 levels, although it is unclear if vitamin B6 supplementation is beneficial (4522,7066,9503).
• Atherosclerosis. Oral vitamin B6 has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: Clinical research in patients with intermediate risk for coronary heart disease shows that taking a specific supplement (Kyolic, Total Heart Health, Formula 108, Wakunga) containing vitamin B6 12.5 mg, aged garlic extract 250 mg, vitamin B12 100 mcg, folic acid 300 mcg, and L-arginine 100 mg daily for 12 months reduces coronary artery calcium progression when compared with placebo (88385). It is unclear if this effect is due to vitamin B6, other ingredients, or the combination.
• Atopic dermatitis (eczema). It is unclear if oral vitamin B6 is beneficial in patients with eczema. Details: A small clinical study in children with eczema shows that taking vitamin B6 (pyridoxine hydrochloride) 50 mg daily for 4 weeks does not reduce symptoms such as redness and itchiness when compared with placebo (83090).
• Attention deficit-hyperactivity disorder (ADHD). It is unclear if oral vitamin B6 is beneficial for ADHD. Details: A small crossover study in children with ADHD shows that taking vitamin B6 600 mg, niacinamide and ascorbic acid 3 grams, and calcium pantothenate 1.2 grams daily for 6 weeks does not improve behavior scores when compared with placebo (9957).
• Autism spectrum disorder. Although there is interest in using oral vitamin B6 for autism, there is insufficient reliable information about the clinical effects of vitamin B6 for this condition.
• Bipolar disorder. It is unclear if oral vitamin B6 is beneficial in patients with bipolar disorder. Details: A small clinical trial in patients with type 1 bipolar disorder who are taking lithium and experiencing an acute episode of mania shows that taking vitamin B6 80 mg daily for 8 weeks does not improve cognitive function or the severity of mania when compared with placebo. Cognitive function was reduced in patients taking vitamin B6; any effect on sleep was unclear (107132).
• Cancer. It is unclear if oral vitamin B6 reduces overall cancer risk. Details: Population research has found that higher dietary intake of vitamin B6 is associated with a 22% reduced risk of cancer, including esophageal, pancreatic, gastric, colorectal, and breast cancer. However, when dietary and supplemental vitamin B6 intake is considered, the inverse association between vitamin B6 and cancer risk is weaker and limited to fewer tumor sites. Furthermore, a meta-analysis of 9 clinical studies shows that taking vitamin B6 3-100 mg orally daily for 2-7.3 years, in combination with vitamin B12 and folate, does not reduce the risk of cancer in patients with cardiovascular disease or kidney failure (96164).
• Cardiovascular disease (CVD). Oral vitamin B6, taken along with other B vitamins, does not seem to improve secondary prevention of death or myocardial infarction in patients with CVD. However, it might slightly lower the risk of stroke. Details: Overall evidence from clinical research and meta-analyses shows that taking vitamin B6 in combination with folic acid and/or vitamin B12 does not seem to help with secondary prevention of death or myocardial infarction in patients with or at risk for CVD (11387,13482,34540,50423,83050,90379,97619). In fact, some research suggests that long-term supplementation with vitamin B6, folic acid, and vitamin B12 for secondary prevention increases the risk of CVD by 20% despite lowering homocysteine levels by 30% (13482). However, some research shows that taking vitamin B6 in combination with other B vitamins modestly reduces the risk of stroke, although results are conflicting (11387,13482,50423,83050,96150,96165,97619,107136). Additionally, it is unclear which specific combination of B vitamins is optimal for reducing stroke risk and which patients are most likely to benefit. In 2001, prior to the publication of the highest quality research on this topic, the US Food and Drug Administration (FDA) approved a qualified health claim stating that, as part of a well-balanced diet that is low in saturated fat and cholesterol, folic acid, vitamin B6, and vitamin B12 may reduce the risk of vascular disease (102368).
• Cognitive function. Oral vitamin B6 has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: A moderate-sized clinical study in healthy adults aged 40-65 years shows that taking a supplement containing vitamin B6, ginkgo leaf, bacopa, and other B vitamins twice daily for 12 weeks does not improve memory or attention when compared with placebo (111334).
• Colorectal cancer. It is unclear if oral vitamin B6 reduces the risk of colorectal cancer. Details: A meta-analysis of observational studies suggests that the highest dietary intake of vitamin B6 is associated with a 20% reduced risk of colorectal cancer when compared with the lowest dietary intake. However, this association was not shown in subgroup analyses of studies conducted in Australia, Europe, or North America (111600). The validity of this analysis is limited by the heterogeneity of the included studies.
• Dental caries. There is limited evidence on the oral use of vitamin B6 for dental decay during pregnancy. Details: Meta-analyses of limited clinical research show that taking vitamin B6 (pyridoxine), 25 mg daily or a single dose of 100 mg orally or intramuscularly, may reduce the risk of dental decay during pregnancy when compared with placebo (83046,96166).
• Depression. It is unclear if oral vitamin B6 reduces the risk of developing depression or improves symptoms of depression. Details: Clinical research in healthy college students shows that taking vitamin B6 100 mg daily for one month does not reduce depression scores when compared with placebo (1104453). However, because a diagnosis of depression was not a requirement for study participation, it is unclear if these findings can be generalized to patients diagnosed with depression. Whether vitamin B6 reduces the risk of developing depression is also unclear. A meta-analysis of population research has found that the highest dietary intake of vitamin B6 is associated with a 19% lower risk of depression when compared with the lowest intake. However, sub-analyses suggest that this association is only relevant in females and not males (107133). In one individual population study in community dwelling older adults included in the analysis, the consumption of at least 1.71 mg of vitamin B6 daily from food was associated with a 43% reduction in the likelihood of becoming depressed when compared with the consumption of 1.33 mg or less daily in females. However, there was no association between vitamin B6 levels and risk of depression in males, and the finding in females was no longer significant when adjusted for total energy intake, since foods rich in vitamin B6 are energy-dense (96168). Another observational longitudinal study in healthy adults starting oral contraceptives containing ethinyl estradiol and levonorgestrel has found that taking vitamin B6 25 mg daily for 6-12 months is associated with a 40% lower risk of depression when compared with no supplementation (90789). Most available studies are cross-sectional in nature, making any conclusions related to causation difficult.
• Diabetes. It is unclear if oral vitamin B6 is beneficial in patients with type 2 diabetes or gestational diabetes. Details: Observational research in Chinese adults with type 2 diabetes has found that dietary intake of vitamin B6 in the highest quartile is associated with 53% lower odds of developing cardiovascular disease, defined as a non-fatal myocardial infarction, non-fatal stroke, or hospitalization for unstable angina, when compared with vitamin B6 intake in the lowest quartile (110452). Small clinical studies in patients with gestational diabetes and vitamin B6 deficiency shows that taking vitamin B6 (pyridoxine) 100 mg daily for 2 weeks improves glucose tolerance and blood glucose levels when compared with baseline (82967,83088). However, there is concern that these findings were confounded by dietary alterations. This benefit was not observed in a subsequent small case series in patients with gestational diabetes (22380).
• Diabetic neuropathy. Oral vitamin B6 has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: Clinical research suggests that taking a combination of B vitamins, including folic acid (L-methylfolate), vitamin B12 (methylcobalamin), and vitamin B6 (pyridoxal-5'-phosphate) for 24 weeks does not improve neural dysfunction based on vibration perception when compared with placebo in patients with diabetic neuropathy. However, taking this combination appears to modestly improve neuropathy symptoms and quality of life related to mental functioning when compared with placebo (90375).
• Dysmenorrhea. It is unclear if oral vitamin B6 is beneficial in patients with dysmenorrhea. Details: Preliminary clinical research shows that taking vitamin B6 (form not specified) 200 mg daily reduces pain associated with dysmenorrhea when compared with placebo. However, taking vitamin B6 in combination with magnesium does not reduce pain when compared with placebo (77388).
• Fibromyalgia. It is unclear if oral vitamin B6 is beneficial in patients with fibromyalgia. Details: A small clinical study in patients with fibromyalgia shows that taking vitamin B6 80 mg daily for 8 weeks does not improve pain, disease severity, anxiety, depression, or quality of life when compared with placebo (110454).
• Gastroenteritis-associated nausea and vomiting. It is unclear if oral vitamin B6 is beneficial in children with gastroenteritis. Details: A small clinical study in children aged 6 months to 12 years with acute viral gastroenteritis shows that taking vitamin B6 (form not specified) does not improve symptoms of dehydration or the frequency of vomiting when compared with placebo (90793).
• Hypertension. It is unclear if oral vitamin B6 reduces blood pressure. Details: One small clinical study in patients with essential hypertension shows that taking vitamin B6 (pyridoxine hydrochloride) 5 mg/kg daily for 4 weeks can reduce systolic and diastolic blood pressure when compared with baseline (83091). The validity of this finding is limited by the lack of a control group.
• Hypertriglyceridemia. It is unclear if oral vitamin B6 reduces triglyceride levels. Details: Preliminary clinical research shows that vitamin B6 (form not specified) 50 mg daily for 12 weeks does not reduce triglyceride levels in people with hypertriglyceridemia when compared with placebo. However, vitamin B6 appears to decrease total cholesterol and high-density lipoprotein (HDL) cholesterol by approximately 9% in these patients (59028).
• Infertility. Although there is interest in using oral vitamin B6 for infertility, there is insufficient reliable information about the clinical effects of vitamin B6 for this condition.
• Insomnia. Oral vitamin B6 has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: Clinical research in healthy adults with self-reported sleep difficulty shows that taking a specific product (LZ Complex3, Sanofi Consumer Healthcare Pty Ltd.) containing vitamin B6, zizyphus extract, hops extract, hydrolyzed milk protein (Lactium), and magnesium oxide nightly, 30 minutes before bed, for 2 weeks does not improve sleep quality, daytime functioning, or physical fatigue when compared with placebo. However, due to the large improvement seen in both the treatment and placebo groups, the effectiveness of this product is unclear (95971).
• Isoniazid-induced neuropathy. It is unclear if oral vitamin B6 prevents the development of neuropathy in patients taking isoniazid. Details: Preliminary clinical research in patients taking isoniazid for tuberculosis shows that taking vitamin B6 (pyridoxine) 6 mg daily reduces the development of neuropathy when compared with control (83068).
• Lactation. It is unclear if oral vitamin B6 helps to suppress postpartum lactation. Details: A meta-analysis of two small clinical trials shows that taking vitamin B6 (pyridoxine) 400-600 mg daily for 6-7 days postpartum does not suppress lactation when compared with no treatment (83047).
• Levetiracetam-induced side effects. While some conflicting evidence exists, several small, low-quality studies suggest that oral vitamin B6 (pyridoxine) may reduce some neuropsychiatric adverse effects related to the use of levetiracetam. Details: In an analysis of case reports, retrospective studies, and a single low-quality prospective study, improvement in levetiracetam-associated neuropsychiatric symptoms occurred in approximately 73% of patients taking pyridoxine (107137). A more recent preliminary clinical trial in children ages 1-17 years shows that taking pyridoxine 10 or 15 mg/kg daily as needed based on symptoms improves behavioral side effects associated with levetiracetam by a small amount when compared with low-dose pyridoxine 0.5 mg/kg daily used as placebo (107124). Also, observational research in children ages 9 months to 14 years has found that taking vitamin B6 is associated with improved behavior and a 44% lower risk of levetiracetam discontinuation when compared with no vitamin B6 supplementation (110455). Some observational research in adults with levetiracetam-associated irritability has found that taking vitamin B6 is associated with an improvement in irritability in 45% of patients when compared to baseline (107129). However, a small clinical trial in adults with epilepsy shows that taking pyridoxine 40 mg daily for 3 weeks does not improve levetiracetam-related psychiatric adverse effects when compared with placebo (110456). This study may have been underpowered to detect differences between groups. Pyridoxine doses used in the studies above have ranged from 50-400 mg daily in children and 40-600 mg daily in adults (107124,107129,107137,110456).
• Lung cancer. It is unclear if dietary or oral vitamin B6 reduces lung cancer risk. Details: Epidemiological research has found that higher serum levels of vitamin B6 in male smokers is associated with a lower risk of lung cancer (9454). Also, people with blood levels of vitamin B6 in the top quartile have a modestly lower risk of lung cancer when compared with those whose levels are in the lowest quartile. The association is stronger for males and for people who have smoked (97999). However, other epidemiological research found that increased dietary intake of vitamin B6 is not associated with a reduced risk of lung cancer (96164).
• Menopausal symptoms. Although there is interest in using oral vitamin B6 for menopausal symptoms, there is insufficient reliable information about the clinical effects of vitamin B6 for this condition.
• Motion sickness. Although there is interest in using oral vitamin B6 for motion sickness, there is insufficient reliable information about the clinical effects of vitamin B6 for this condition.
• Nausea and vomiting. It is unclear if oral vitamin B6 is beneficial for nausea and vomiting in patients using oral contraceptives. Details: An observational longitudinal study in healthy females taking oral contraceptives containing ethinyl estradiol and levonorgestrel has found that taking vitamin B6 25 mg daily for 6-12 months is associated with a 43% reduced risk of nausea when compared with no supplementation (90789).
• Nonalcoholic fatty liver disease (NAFLD). It is unclear if oral vitamin B6 for patients with NAFLD. Details: A small clinical trial in patients with NAFLD shows that taking vitamin B6 (pyridoxine) 30 mg three times daily for 12 weeks does not reduce levels of liver transaminases or plasma lipids when compared with baseline. However, hepatic fat accumulation was modestly reduced (107130). The validity of this study is limited by the lack of a comparator group.
• Obesity. It is unclear if oral vitamin B6 in beneficial in overweight or obese individuals. Details: A small clinical trial in females with a body mass index (BMI) of at least 25 kg/m² shows that taking vitamin B6 as pyridoxine 80 mg daily for 8 weeks reduces fat mass and improves insulin resistance and triglyceride levels by a small amount when compared with placebo. Although some other anthropometric and metabolic indices were improved when compared with baseline, there was no effect of pyridoxine on body weight, visceral adiposity, or other endpoints when compared with placebo (107131).
• Overall mortality. It is unclear if oral vitamin B6 reduces the risk of overall mortality. Details: Observational research in US adults has found that dietary intake of vitamin B6 in the highest quintile is associated with a 12% to 21% lower risk of all-cause mortality and a 31% to 44% lower risk of cardiovascular mortality when compared with the lowest quintile of dietary vitamin B6 intake (110451).
• Pancreatic cancer. It is unclear if oral vitamin B6 reduces the risk of pancreatic cancer. Details: Observational research has found that higher dietary intake of vitamin B6 is associated with a 37% lower risk of developing pancreatic cancer when compared with lower intake (104927).
• Postpartum depression. It is unclear if oral vitamin B6 is beneficial in patients with postpartum depression. Details: Preliminary clinical research in individuals considered at increased risk for postpartum depression, but without clinical depression, shows that taking vitamin B6 80 mg daily from the 28th week of pregnancy until birth, and then 40 mg daily for one month, reduces symptoms of depression 1.5 months after birth when compared with baseline (measured during the third trimester) and when compared with placebo. However, it is unclear if any of the patients included in the study developed postpartum depression, as there were no changes in overall symptoms in patients taking placebo (107126).
• Restless legs syndrome (RLS). It is unclear if oral vitamin B6 is beneficial in patients with RLS. Details: A small clinical study in adults with RLS who are beginning treatment with pramipexole shows that also taking vitamin B6 40 mg daily for 2 months moderately improves RLS scores and sleep quality scores when compared with pramipexole and placebo (110052).
• Schizophrenia. It is unclear if oral vitamin B6 is beneficial for patients with treatment-resistant schizophrenia. Details: Clinical research in male patients with treatment-resistant schizophrenia who are on a consistent antipsychotic dose shows that adding vitamin B6 300 mg twice daily for 16 weeks modestly improves psychotic symptoms and some measures of cognitive performance when compared with adding aripiprazole 5 mg twice daily (107128). More research is needed to determine if these benefits are clinically relevant.
• Seizures. It is unclear if oral vitamin B6 is beneficial for preventing seizures in patients with glycosylphosphatidylinositol (GPI) deficiency. Details: Observational case series in a small number of children and young adults with GPI deficiency has found that taking vitamin B6 20-30 mg/kg daily for 3-12 months is associated with some reduction in seizure frequency in 9 of 13 patients. However, no patient reached seizure freedom (107125,107135). In one case series, treatment for 12 months was associated with modest developmental improvements in almost all patients (107135). The study patient populations were slightly different in terms of age and underlying genetic causes for GPI deficiency.
• Sickle cell disease. Oral vitamin B6 has only been evaluated in combination with other B vitamins; its effect when used alone is unclear. Details: Preliminary clinical research in adults with sickle cell disease shows that taking vitamin B6 4.2-6 mg, vitamin B12 4.2-6 mcg, and folic acid 700 mcg daily might lower homocysteine levels. However, it is unknown if this will reduce the risk of endothelial damage in these patients (9324).
• Stroke. It is unclear if oral vitamin B6, either alone or with other B vitamins, is beneficial for stroke prevention. Details: There is some debate about whether supplementation with homocysteine-lowering B vitamins, including vitamin B6, can reduce the risk of stroke. A number of clinical studies and meta-analyses show that supplementation with folic acid, vitamin B6, and vitamin B12, alone or in combination, does not reduce the risk of stroke in patients with cardiovascular disease (CVD) or impaired kidney function (11387,13482,50423,83050,96150). However, a more recent meta-analysis of 10 clinical trials, including over 44,000 patients at risk for or with a history of CVD, shows that B vitamin supplementation reduces the relative risk of stroke by 10% when compared with placebo (97619). This meta-analysis differed from some of the earlier analyses due to the inclusion of several additional clinical trials. Also, another meta-analysis of three clinical trials including 9900 patients with a history of stroke shows that B vitamin supplementation reduces the relative risk of stroke recurrence by 13% when compared with placebo, although this finding was determined to have a low level of certainty. Based on two clinical trials, there was also a 17% reduced risk of vascular death and an 11% reduction in the combined risk of stroke, myocardial infarction, and vascular death (107136). In 2001, prior to the publication of the highest quality research on this topic, the US Food and Drug Administration (FDA) allowed a qualified health claim stating that, as part of a well-balanced diet that is low in saturated fat and cholesterol, folic acid, vitamin B6, and vitamin B12 may reduce the risk of vascular disease (102368). Unfortunately, even after the publication of higher quality research, it is still unclear which specific combination of B vitamins is optimal and which patients are most likely to benefit. One network meta-analysis shows that a combination of folic acid and vitamin B6 lowers the risk of stroke more effectively than B vitamin mixtures that include vitamin B12 (96165). However, this analysis is limited because it didn't account for dosing. Exposure to low, but not high amounts, of vitamin B12 (cyanocobalamin) seems to reduce stroke risk (96150).
• Tardive dyskinesia. It is unclear if oral vitamin B6 prevents tardive dyskinesia in patients taking neuroleptic drugs. Details: A small clinical study in patients taking neuroleptic drugs for schizophrenia shows that taking vitamin B6 (form not specified) 400 mg daily seems to improve Parkinsonian, dystonic, and dyskinetic symptoms when compared with placebo (8558).
• Tourette syndrome. Oral vitamin B6 has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: A small, nonblinded clinical study in children aged 4-17 years with untreated Tourette syndrome or with chronic tic disorder and associated symptoms of anxiety shows that taking a liquid nutritional supplement providing vitamin B6 2.8 mg and L-theanine 200 mg daily for 2 months improves scores on the Yale Global Tic Severity Scale, but does not reduce anxiety, when compared with patients receiving psychoeducation (108555). This study may have been inadequately powered to detect a difference between groups.
• Vincristine-induced neuropathy. Oral vitamin B6 has only been evaluated in combination with pyridostigmine; its effect when used alone is unclear. Details: A small clinical study in children ages 11 months to 13 years with neuropathy due to vincristine treatment for acute lymphoblastic leukemia, shows that taking vitamin B6 150 mg/m2 and pyridostigmine 3 mg/kg twice daily for 3 months is associated with reduced severity of sensory and motor neuropathy when compared with baseline (104928). The validity of this finding is limited by the lack of a control group. More evidence is needed to rate vitamin B6 for these uses.

(Read more about VITAMIN B6)

LIKELY SAFE ...when used orally and appropriately. Acetyl-L-carnitine has been used safely in doses up to 3 grams daily in clinical trials lasting up to 33 months (42,1589,1594,1595,1596,1597,1598,1599,3600,3601) (9105,9791,10076,12743,12745,58375,90755,90756,90759,90761)(90766,90767,90768,95063,95067,111862).

POSSIBLY SAFE ...when used parenterally and appropriately under medical supervision (1591,1592,12743).

CHILDREN: POSSIBLY SAFE
when used orally and appropriately, short-term. Acetyl-L-carnitine has been safely used orally in children for up to 6 weeks (90754).

PREGNANCY AND LACTATION:
Insufficient reliable information available; avoid using.

(Read more about ACETYL-L-CARNITINE)

POSSIBLY SAFE ...when used orally and appropriately. Alpha-GPC has been used with apparent safety at doses of 400 mg three times daily (1200 mg/day) for up to 6 months (12102,12176). ...when used intramuscularly and appropriately. Alpha-GPC has been administered intramuscularly with apparent safety at doses of 1000-1200 mg/day for 28 to 90 days (12100,12102).

PREGNANCY AND LACTATION:
Insufficient reliable information available; avoid using.

(Read more about ALPHA-GPC)

LIKELY SAFE ...when used orally and appropriately. Choline is safe in adults when taken in doses below the tolerable upper intake level (UL) of 3.5 grams daily (3094) ...when used intravenously and appropriately. Intravenous choline 1-4 grams daily for up to 24 weeks has been used with apparent safety (5173,5174).

POSSIBLY UNSAFE ...when used orally in doses above the tolerable upper intake level (UL) of 3. 5 grams daily. Higher doses can increase the risk of adverse effects (3094).

CHILDREN: LIKELY SAFE
when used orally and appropriately (3094). Choline is safe in children when taken in doses below the tolerable upper intake level (UL), which is 1 gram daily for children 1-8 years of age, 2 grams daily for children 9-13 years of age, and 3 grams daily for children 14-18 years of age (3094).

CHILDREN: POSSIBLY UNSAFE
when used orally in doses above the UL. High doses can increase the risk of adverse effects (3094).

PREGNANCY AND LACTATION: LIKELY SAFE
when used orally and appropriately. Choline is safe when taken in doses below the tolerable upper intake level (UL), which is 3 grams daily during pregnancy and lactation in those up to 18 years of age and 3.5 grams daily for those 19 years and older (3094,92114). There is insufficient reliable information available about the safety of choline used in higher doses during pregnancy and lactation.

(Read more about CHOLINE)

LIKELY SAFE ...when used orally or parenterally and appropriately. Folic acid has been safely used in amounts below the tolerable upper intake level (UL). The UL for folic acid is based only on supplemental folic acid and is expressed in mcg folic acid. Dietary folate is not included in UL calculations, as dietary folate consumption has not been associated with adverse effects. The UL for folic acid in adults is 1000 mcg (6241). In cases of megaloblastic anemia resulting from folate deficiency or malabsorption disorders such as sprue, oral doses of 1-5 mg per day can also be used safely until hematologic recovery is documented, as long as vitamin B12 levels are routinely measured (6241,7725,8739).

POSSIBLY SAFE ...when L-5-methyltetrahydrofolate (L-5-MTHF), the reduced form of folate, is used orally and appropriately, short-term. L-5-MTHF has been used with apparent safety at a dose of 416 mcg daily for 16 weeks (104913,104914) and a dose of 113 mcg daily for 24 weeks (104920). A specific L-5-MTHF product (Metafolin, Eprova) has been used with apparent safety at a dose of 1.3 mg daily for 12 weeks (104912).

POSSIBLY UNSAFE ...when used orally in large doses, long-term. Clinical research shows that taking folic acid daily in doses of 800 mcg to 1200 mcg for 3-10 years significantly increases the risk of developing cancer and adverse cardiovascular effects compared to placebo (12150,13482,16822,17041). Doses above 1 mg per day should also be avoided if possible to prevent precipitation or exacerbation of neuropathy related to vitamin B12 deficiency (6241,6242,6245). However, there is contradictory evidence suggesting that higher doses may not be harmful. There is some evidence that doses of 5 mg per day orally for up to 4 months can be used safely if vitamin B12 levels are routinely measured (7725). Also, other clinical research suggests that folic acid supplementation at doses up to 5 mg, usually in combination with vitamin B12, does not increase the risk of cancer when taken for 2-7 years (91312). Very high doses of 15 mg per day can cause significant central nervous system (CNS) and gastrointestinal side effects (505).

CHILDREN: LIKELY SAFE
when used orally and appropriately. Folic acid has been safely used in children in amounts below the tolerable upper intake level (UL). The ULs for folic acid are based only on supplemental folic acid and are expressed in mcg folic acid. Dietary folate is not included in UL calculations, as dietary folate consumption has not been associated with adverse effects. The UL for children is: 1-3 years of age, 300 mcg; 4-8 years of age, 400 mcg; 9-13 years of age, 600 mcg; 14-18 years of age, 800 mcg (6241).

CHILDREN: POSSIBLY SAFE
when L-5-methyltetrahydrofolate (L-5-MTHF), the reduced form of folate, is used orally and appropriately. One clinical study in infants aged 27 days and younger shows that consuming a formula containing L-5-MTHF (Metafolin, Merck & Cie) 10.4 mcg/100 mL daily has been used with apparent safety for up to 12 weeks (104918).

PREGNANCY AND LACTATION: LIKELY SAFE
when used orally and appropriately. Folic acid 300-400 mcg is commonly used during pregnancy for prevention of neural tube defects (8739). Miscarriage rates and negative impacts on fetal growth have not been shown to increase with peri-conception supplemental folic acid intakes of 4 mg per day (91320,91322). However, other research shows that taking more than 5 mg per day during pregnancy may reduce development of cognitive, emotional, and motor skills in infants (91318). Also, the tolerable upper intake level (UL) of folic acid for pregnant or lactating women is 800 mcg daily for those 14-18 years of age and 1000 mcg daily for those 19 years and older (6241).

PREGNANCY AND LACTATION: POSSIBLY SAFE
when L-5-methyltetrahydrofolate (L-5-MTHF), the reduced form of folate, is used orally and appropriately, short-term. L-5-MTHF has been used with apparent safety at a dose of 416 mcg daily for 16 weeks during lactation. Compared to folic acid, this form seems to further increase the folate concentration of red blood cells, but not breast milk (104913,104914).

(Read more about FOLIC ACID)

LIKELY SAFE ...when niacin is taken in food or as a supplement in amounts below the tolerable upper intake level (UL) of 30 mg daily for adults 18 years of age and 35 mg daily for adults 19 years and older (6243). ...when prescription products are used orally and appropriately in doses of up to 2 grams daily (12033). CHILDREN:

LIKELY SAFE ...when used orally in amounts that do not exceed the tolerable upper intake level (UL). The ULs of niacin for children are: 1-3 years of age, 10 mg daily; 4-8 years of age, 15 mg daily; 9-13 years of age, 20 mg daily; 14-18 years of age, 30 mg daily (6243).

PREGNANCY AND LACTATION: LIKELY SAFE
when used orally in amounts that do not exceed the tolerable upper intake level (UL). The UL of niacin during pregnancy and lactation is 30 mg daily for 14-18 years of age and 35 mg daily for 19 years and older (6243). There is insufficient reliable information available about the safety of larger oral doses of niacin during pregnancy or lactation; avoid using.

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POSSIBLY SAFE ...when used orally and appropriately. Phosphatidylserine has been used with apparent safety at dose of up to 300 mg daily for up to 6 months (2255,2437,2438,2439,2440,2441,7118,15539,68855).

CHILDREN: POSSIBLY SAFE
when used orally and appropriately, short-term (7117). Phosphatidylserine has been used with apparent safety in clinical research in doses of 200-300 mg daily for up to 4 months in children aged 4-18 years (7117,89498).

PREGNANCY AND LACTATION:
Insufficient reliable information available; avoid using.

(Read more about PHOSPHATIDYLSERINE)

LIKELY SAFE ...when used orally in amounts commonly found in foods. Tyrosine has Generally Recognized as Safe (GRAS) status in the US (4912).

POSSIBLY SAFE ...when used orally and appropriately in medicinal amounts, short-term. Tyrosine has been used safely in doses up to 150 mg/kg daily for up to 3 months (7210,7211,7215). ...when used topically and appropriately (6155).

PREGNANCY AND LACTATION:
There is insufficient reliable information available about the safety of tyrosine during pregnancy and lactation when used in medicinal amounts. Some pharmacokinetic research shows that taking a single dose of tyrosine 2-10 grams orally can modestly increase levels of free tyrosine in breast milk. However, total levels are not affected, and levels remain within the range found in infant formulas. Therefore, it is not clear if the increase in free tyrosine is a concern (91467).

(Read more about TYROSINE)

LIKELY SAFE ...when used orally, topically, intravenously, intramuscularly, or intranasally and appropriately. Vitamin B12 is generally considered safe, even in large doses (15,1344,1345,1346,1347,1348,2909,6243,7289,7881)(9414,9416,10126,14392,15765,82832,82949,82860,82864,90386)(111334,111551).

PREGNANCY: LIKELY SAFE
when used orally in amounts that do not exceed the recommended dietary allowance (RDA). The RDA for vitamin B12 during pregnancy is 2.6 mcg daily (6243). There is insufficient reliable information available about the safety of larger amounts of vitamin B12 during pregnancy.

LACTATION: LIKELY SAFE
when used orally in amounts that do not exceed the recommended dietary allowance (RDA). The RDA of vitamin B12 during lactation is 2.8 mcg daily (6243). There is insufficient reliable information available about the safety of larger amounts of vitamin B12 while breastfeeding.

(Read more about VITAMIN B12)

LIKELY SAFE ...when used orally and appropriately in doses that do not exceed the tolerable upper intake level (UL) of 100 mg daily for adults (15). ...when used parenterally and appropriately. Injectable vitamin B6 (pyridoxine) is an FDA-approved prescription product (15).

POSSIBLY SAFE ...when used orally and appropriately in doses of 101-200 mg daily (6243,8558).

POSSIBLY UNSAFE ...when used orally in doses at or above 500 mg daily. High doses, especially those exceeding 1000 mg daily or total doses of 1000 grams or more, pose the most risk. However, neuropathy can occur with lower daily or total doses (6243,8195). ...when used intramuscularly in high doses and frequency due to potential for rhabdomyolysis (90795).

CHILDREN: LIKELY SAFE
when used orally and appropriately (3094).

CHILDREN: POSSIBLY SAFE
when used orally and appropriately in amounts exceeding the recommended dietary allowance (5049,8579,107124,107125,107135).

CHILDREN: POSSIBLY UNSAFE
when used orally in excessive doses, long-term (3094).

PREGNANCY: LIKELY SAFE
when used orally and appropriately. A special sustained-release product providing vitamin B6 (pyridoxine) 75 mg daily is FDA-approved for use in pregnancy. Vitamin B6 (pyridoxine) is also considered a first-line treatment for nausea and vomiting in pregnancy by the American College of Obstetrics and Gynecology (111601). However, it should not be used long-term or without medical supervision and close monitoring.

PREGNANCY: POSSIBLY UNSAFE
when used orally in excessive doses. There is some concern that high-dose maternal vitamin B6 (pyridoxine) can cause neonatal seizures (4609,6397,8197).

LACTATION: LIKELY SAFE
when used orally in doses not exceeding the recommended dietary allowance (RDA) (3094). The RDA in lactating women is 2 mg daily. There is insufficient reliable information available about the safety of vitamin B6 when used in higher doses in breast-feeding women.

(Read more about VITAMIN B6)

ACENOCOUMAROL (Sintrom) Interaction Rating = Moderate Be cautious with this combination. Severity = High •  Occurrence = Possible •  Level of Evidence = D Theoretically, acetyl-L-carnitine might increase the anticoagulant effects of acenocoumarol.  Details L-carnitine, the parent compound of acetyl-L-carnitine, might enhance the anticoagulant effects of acenocoumarol, an oral anticoagulant that is similar to warfarin, but shorter-acting (9878,12165). There are at least two case reports of INR elevation when L-carnitine was taken with acenocoumarol. In one case, a 33-year-old male with a previously stable INR had an elevated INR of 4.65 after L-carnitine was started and continued for 10 weeks. INR normalized after discontinuation of the L-carnitine-containing product (12165). It is unclear if such an interaction would also occur with acetyl-L-carnitine.

SEROTONERGIC DRUGS Interaction Rating = Moderate Be cautious with this combination. Severity = High •  Occurrence = Possible •  Level of Evidence = D Theoretically, acetyl-L-carnitine might increase the risk of serotonergic side effects, including serotonin syndrome and cerebral vasoconstrictive disorders, when taken with serotonergic drugs.  Details Animal research shows that acetyl-L-carnitine can increase levels of serotonin in the brain (95065).

THYROID HORMONE Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Probable •  Level of Evidence = B Theoretically, acetyl-L-carnitine might decrease the effectiveness of thyroid hormone replacement.  Details L-carnitine appears to act as a peripheral thyroid hormone antagonist by inhibiting entry of thyroid hormone into the nucleus of cells (12761). Taking L-carnitine also seems to diminish some of the symptoms of hyperthyroidism (8047). It is unclear if such an interaction would occur with acetyl-L-carnitine.

WARFARIN (Coumadin) Interaction Rating = Moderate Be cautious with this combination. Severity = High •  Occurrence = Possible •  Level of Evidence = D Theoretically, acetyl-L-carnitine might increase the anticoagulant effects of warfarin.  Details L-carnitine, the parent compound of acetyl-L-carnitine, might increase the anticoagulant effects of acenocoumarol, a shorter-acting oral anticoagulant similar to warfarin (9878,12165). There is not enough information to know whether this interaction occurs with acetyl-L-carnitine and warfarin.

(Read more about ACETYL-L-CARNITINE)

SCOPOLAMINE (Transderm Scop) Interaction Rating = Minor Be watchful with this combination. Severity = Mild •  Occurrence = Possible •  Level of Evidence = B Theoretically, alpha-GPC might decrease the effects of scopolamine.  Details A small clinical study shows that alpha-GPC can partially counteract the attention and memory impairment effects caused by scopolamine given intramuscularly (12103). Whether alpha-GPC can decrease the beneficial anti-motion sickness effects of the scopolamine patch (Transderm Scop) is unclear.

(Read more about ALPHA-GPC)

ATROPINE Interaction Rating = Minor Be watchful with this combination. Severity = Mild •  Occurrence = Possible •  Level of Evidence = D Theoretically, choline might decrease the effects of atropine in the brain.  Details Animal research shows that administering choline one hour before administering atropine can attenuate atropine-induced decreases in brain levels of acetylcholine (42240). Theoretically, concomitant use of choline and atropine may decrease the effects of atropine.

(Read more about CHOLINE)

5-FLUOROURACIL Interaction Rating = Moderate Be cautious with this combination. Severity = High •  Occurrence = Possible •  Level of Evidence = D Theoretically, high doses of folic acid might increase the toxicity of 5-fluorouracil.  Details Increases in gastrointestinal side effects of 5-fluorouracil, such as stomatitis and diarrhea, have been described in two clinical studies when leucovorin, a form of folic acid, was administered with 5-fluorouracil (16845).

CAPECITABINE (Xeloda) Interaction Rating = Moderate Be cautious with this combination. Severity = High •  Occurrence = Possible •  Level of Evidence = D Use of high-dose folic acid might contribute to capecitabine toxicity.  Details Clinical research suggests that higher serum folate levels are associated with an increased risk for moderate or severe toxicity during capecitabine-based treatment for colorectal cancer (105402). Additionally, in one case report, taking folic acid 15 mg daily might have contributed to increased toxicity, including severe diarrhea, vomiting, edema, hand-foot syndrome, and eventually death, in a patient prescribed capecitabine (16837).

METHOTREXATE (Trexall, others) Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Probable •  Level of Evidence = B Folic acid might reduce the efficacy of methotrexate as a cancer treatment when given concurrently.  Details Methotrexate exerts its cytotoxic effects by preventing conversion of folic acid to the active form needed by cells. There is some evidence that folic acid supplements reduce the efficacy of methotrexate in the treatment of acute lymphoblastic leukemia, and theoretically they could reduce its efficacy in the treatment of other cancers (9420). Advise cancer patients to consult their oncologist before using folic acid supplements. In patients treated with long-term, low-dose methotrexate for rheumatoid arthritis (RA) or psoriasis, folic acid supplements can reduce the incidence of side effects, without reducing efficacy (768,2162,4492,4493,4494,4546,9369).

PHENOBARBITAL (Luminal) Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Probable •  Level of Evidence = B Folic acid might have antagonistic effects on phenobarbital and increase the risk for seizures.  Details Folic acid can have direct convulsant activity in some people, reversing the effects of phenobarbital and worsening seizure control (4427,9357,9358). Monitor closely for increased seizure activity.

PHENYTOIN (Dilantin) Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Probable •  Level of Evidence = B Folic acid might reduce serum levels of phenytoin in some patients.  Details Folic acid may be a cofactor in phenytoin metabolism (4471). Folic acid, in doses of 1 mg daily or more, can reduce serum levels of phenytoin in some patients (4471,4477,4531,4536). Increases in seizure frequency have been reported. If folic acid supplements are added to established phenytoin therapy, monitor serum phenytoin levels closely. If phenytoin and folic acid are started at the same time and continued together, adverse changes in phenytoin pharmacokinetics are avoided (4471,4472,4473,4531). Note that phenytoin also reduces serum folate levels.

PRIMIDONE (Mysoline) Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Probable •  Level of Evidence = B Folic acid might have antagonistic effects on primidone and increase the risk for seizures.  Details Folic acid can have direct convulsant activity in some people, reversing the effects of primidone and worsening seizure control (4427,9357,9358). Monitor closely for increased seizure activity. Note that primidone also reduces serum folate levels.

PYRIMETHAMINE (Daraprim) Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Probable •  Level of Evidence = D Folic acid might antagonize the effects of pyrimethamine.  Details Folic acid can antagonize the antiparasitic effects of pyrimethamine against toxoplasmosis and Pneumocystis carinii pneumonia. Folic acid doesn't antagonize the effects of pyrimethamine in the treatment of malaria, because malarial parasites cannot use exogenous folic acid. Use folinic acid as an alternative to folic acid when indicated (9380).

(Read more about FOLIC ACID)

ALCOHOL (Ethanol) Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Probable •  Level of Evidence = D Concomitant use of alcohol and niacin might increase the risk of flushing and hepatotoxicity.  Details Alcohol can exacerbate the flushing and pruritus associated with niacin (4458,11689). Large doses of niacin might also exacerbate liver dysfunction associated with chronic alcohol use. A case report describes delirium and lactic acidosis in a patient taking niacin 3 grams daily who ingested 1 liter of wine (14510). Advise patients to avoid large amounts of alcohol while taking niacin.

ALLOPURINOL (Zyloprim) Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Probable •  Level of Evidence = C Theoretically, niacin might antagonize the therapeutic effects of uricosurics such as allopurinol.  Details Large doses of niacin can reduce urinary excretion of uric acid, potentially resulting in hyperuricemia (4860,4863,12033). Doses of uricosurics such as allopurinol might need to be increased to maintain control of gout in patients who start taking niacin (4458). People who have frequent attacks of gout despite uricosuric therapy should avoid niacin (4863).

ANTICOAGULANT/ANTIPLATELET DRUGS Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Possible •  Level of Evidence = D Theoretically, niacin may have additive effects when used with anticoagulant or antiplatelet drugs.  Details Several cases of clotting factor synthesis deficiency and coagulopathy have been reported in patients taking sustained-release niacin (25915). Also, thrombocytopenia has been reported in patients treated with niacin or niacin plus lovastatin (25916).

ANTIDIABETES DRUGS Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Probable •  Level of Evidence = B Niacin can increase blood glucose levels and may diminish the effects of antidiabetes drugs.  Details Niacin impairs glucose tolerance in a dose-dependent manner, probably by causing or aggravating insulin resistance and increasing hepatic production of glucose (4860,4863,11692,11693). In diabetes patients, niacin 4.5 grams daily for 5 weeks can increase plasma glucose by an average of 16% and glycated hemoglobin (HbA1c) by 21% (4860). However, lower doses of 1.5 grams daily or less appear to have minimal effects on blood glucose (12033). In some patients, glucose levels increase when niacin is started, but then return to baseline when a stable dose is reached (12033,93344). Up to 35% of patients with diabetes may need adjustments in hypoglycemic therapy when niacin is added (4458,4860,4863,11689,12033).

ANTIHYPERTENSIVE DRUGS Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Possible •  Level of Evidence = B Theoretically, niacin may increase the risk of hypotension when used with antihypertensive drugs.  Details The vasodilating effects of niacin can cause hypotension (4863,12033,93341). Furthermore, some clinical evidence suggests that a one-hour infusion of niacin can reduce systolic, diastolic, and mean blood pressure in hypertensive patients. This effect is not observed in normotensive patients (25917).

ASPIRIN Interaction Rating = Minor Be watchful with this combination. Severity = Insignificant •  Occurrence = Likely •  Level of Evidence = B Large doses of aspirin might alter the clearance of niacin.  Details Aspirin is often used with niacin to reduce niacin-induced flushing (4458,11689). Doses of 80-975 mg aspirin have been used, but 325 mg appears to be optimal (4458,4852,4853,11689). Aspirin also seems to reduce the clearance of niacin by competing for glycine conjugation. Taking aspirin 1 gram seems to reduce niacin clearance by 45% (14524). This is probably a dose-related effect and not clinically significant with the more common aspirin dose of 325 mg (11689,14524).

BILE ACID SEQUESTRANTS Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Possible •  Level of Evidence = D Bile acid sequestrants can bind niacin and decrease absorption. Separate administration by 4-6 hours to avoid an interaction.  Details In vitro studies show that colestipol (Colestid) binds about 98% of available niacin and cholestyramine (Questran) binds 10% to 30% (14511).

GEMFIBROZIL (Lopid) Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Possible •  Level of Evidence = D Theoretically, concomitant use of niacin and gemfibrozil might increase the risk of myopathy in some patients.  Details A case of myopathy from concomitant use of niacin and gemfibrozil has been reported (25920). Niacin alone has also been associated with cases of myopathy (26100,26111). Using gemfibrozil with niacin might further increase the risk of developing myopathy.

HEPATOTOXIC DRUGS Interaction Rating = Moderate Be cautious with this combination. Severity = High •  Occurrence = Possible •  Level of Evidence = D Theoretically, concomitant use of niacin and hepatotoxic drugs might increase the risk of hepatotoxicity.  Details Niacin has been associated with cases of liver toxicity, especially when used in pharmacologic doses (4863,11689,11691,25929,25930,25931). Sustained-release niacin preparations appear to be associated with a higher risk of hepatotoxicity than immediate-release niacin (11691,25930,25931,93342).

HMG-CoA REDUCTASE INHIBITORS ("Statins") Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Possible •  Level of Evidence = D Theoretically, concomitant use of niacin and statins might increase the risk of myopathy and rhabdomyolysis in some patients.  Details Some case reports have raised concerns that niacin might increase the risk of myopathy and rhabdomyolysis when combined with statins (14508,25918). However, a significantly increased risk of myopathy has not been demonstrated in clinical trials, including those using an FDA-approved combination of lovastatin and niacin (Advicor) (7388,11689,12033,14509).

PROBENECID (Benemid) Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Probable •  Level of Evidence = C Theoretically, niacin might antagonize the therapeutic effects of uricosurics such as probenecid.  Details Large doses of niacin reduce urinary excretion of uric acid, potentially causing hyperuricemia (4863,12033). Doses of uricosurics such as probenecid might need to be increased to maintain control of gout in patients who start taking niacin (4458). People who have frequent attacks of gout despite uricosuric therapy should avoid niacin (4863).

SULFINPYRAZONE (Anturane) Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Probable •  Level of Evidence = C Theoretically, niacin might antagonize the therapeutic effects of uricosurics such as sulfinpyrazone.  Details Large doses of niacin reduce urinary excretion of uric acid, potentially causing hyperuricemia (4863,12033). Doses of uricosurics such as sulfinpyrazone might need to be increased to maintain control of gout in patients who start taking niacin (4458). People who have frequent attacks of gout despite uricosuric therapy should avoid niacin (4863).

THYROID HORMONE Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Probable •  Level of Evidence = D Theoretically, niacin might antagonize the therapeutic effects of thyroid hormones.  Details Clinical research and case reports suggests that taking niacin can reduce serum levels of thyroxine-binding globulin by up to 25% and moderately reduce levels of thyroxine (T4) (25916,25925,25926,25928). Patients taking thyroid hormone for hypothyroidism might need dose adjustments when using niacin.

TRANSDERMAL NICOTINE (Nicoderm) Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Possible •  Level of Evidence = D Theoretically, concomitant use of niacin and transdermal nicotine might increase the risk of flushing and dizziness.  Details Niacin and nicotine can both cause flushing and dizziness (496,96211).

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ANTICHOLINERGIC DRUGS Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Possible •  Level of Evidence = B Theoretically, phosphatidylserine might decrease the effectiveness anticholinergic drugs.  Details Phosphatidylserine is thought to increase acetylcholine levels (2437,8857,8858), which could theoretically interfere with the activity of anticholinergic agents.

CHOLINERGIC DRUGS Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Possible •  Level of Evidence = B Theoretically, phosphatidylserine might have additive effects with cholinergic drugs.  Details Phosphatidylserine is thought to increase acetylcholine levels (2437,8857,8858), which could theoretically lead to additive cholinergic effects when used with cholinergic drugs.

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LEVODOPA Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Probable •  Level of Evidence = D Theoretically, tyrosine might decrease the effectiveness of levodopa.  Details Tyrosine and levodopa compete for absorption in the proximal duodenum by the large neutral amino acid (LNAA) transport system (2719). Advise patients to separate doses of tyrosine and levodopa by at least 2 hours.

THYROID HORMONE Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Probable •  Level of Evidence = D Theoretically, tyrosine might have additive effects with thyroid hormone medications.  Details Tyrosine is a precursor to thyroxine and might increase levels of thyroid hormones (7212).

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(Read more about VITAMIN B12)

AMIODARONE (Cordarone) Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Possible •  Level of Evidence = B Theoretically, vitamin B6 might increase the photosensitivity caused by amiodarone.  Details Despite initial case reports suggesting that pyridoxine may have a protective effect against amiodarone-induced photosensitivity, preliminary clinical research suggests that pyridoxine may actually exacerbate this adverse effect (8892,8893).

ANTIHYPERTENSIVE DRUGS Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Possible •  Level of Evidence = B Theoretically, vitamin B6 may have additive effects when used with antihypertensive drugs.  Details Research in hypertensive rats shows that vitamin B6 can decrease systolic blood pressure (30859,82959,83093). Similarly, clinical research in patients with hypertension shows that taking high doses of vitamin B6 may reduce systolic and diastolic blood pressure, possibly by reducing plasma levels of epinephrine and norepinephrine (83091).

LEVODOPA Interaction Rating = Minor Be watchful with this combination. Severity = Moderate •  Occurrence = Unlikely •  Level of Evidence = D Vitamin B6 may increase the metabolism of levodopa when taken alone, but not when taken in conjunction with carbidopa.  Details Vitamin B6 (pyridoxine) enhances the metabolism of levodopa, reducing its clinical effects. However, this interaction does not occur when carbidopa is used concurrently with levodopa (Sinemet). Therefore, it is not likely to be a problem in most people (3046).

PHENOBARBITAL (Luminal) Interaction Rating = Moderate Be cautious with this combination. Severity = High •  Occurrence = Possible •  Level of Evidence = D High doses of vitamin B6 may reduce the levels and clinical effects of phenobarbital.  Details Preliminary clinical evidence suggests that vitamin B6 200 mg daily can reduce plasma levels of phenobarbital, possibly by increasing metabolism. It is not known whether lower doses have any effect. Advise people taking phenobarbital to avoid high doses of vitamin B6 (3046,10801).

PHENYTOIN (Dilantin) Interaction Rating = Moderate Be cautious with this combination. Severity = High •  Occurrence = Possible •  Level of Evidence = D High doses of vitamin B6 may reduce the levels and clinical effects of phenytoin.  Details Preliminary clinical evidence suggests that vitamin B6 200 mg daily can reduce plasma levels of phenytoin, possibly by increasing metabolism. It is not known whether lower doses have any effect. Advise people taking phenytoin to avoid high doses of vitamin B6 (3046,10801).

(Read more about VITAMIN B6)

General ...Orally, acetyl-L-carnitine is generally well tolerated.
Most Common Adverse Effects:
Orally: Agitation, dry mouth, headache, insomnia, and reduced appetite. A metabolite of acetyl-L-carnitine has been reported to cause a fishy odor of the urine, breath, and sweat.

Cardiovascular ...Orally, one patient in a pharmacokinetic study reported high blood pressure 8 hoursafter taking acetyl-L-carnitine 500 mg; however, it is unclear if this was due to acetyl-L-carnitine or another factor (95061).

Dermatologic ...Orally, a combination of acetyl-L-carnitine and alpha-lipoic acid may cause rash (90441).

Gastrointestinal ...Orally, acetyl-L-carnitine may cause nausea, vomiting, diarrhea, constipation, hiccups, abdominal distension and gastrointestinal upset or pain. However, gastrointestinal symptoms do not usually occur more often in patients receiving acetyl-L-carnitine than in patients receiving placebo (1596,1599,12743,13007,58922,90755,95063,95067,111889,111894). Acetyl-L-carnitine may also cause dry mouth and anorexia (58342). When taken orally, a combination of acetyl-L-carnitine and alpha-lipoic acid may cause diarrhea, constipation, and dyspepsia (90441).

Neurologic/CNS ...Orally, acetyl-L-carnitine may cause headache and insomnia (90760,90767,95063). In one clinical trial, two patients with antiretroviral toxic neuropathy reported paresthesia, pain, and neuropathy after taking acetyl-L-carnitine 1000 mg daily (58342). A case of mania has been reported for a patient with bipolar I disorder currently in remission. The patient presented with symptoms after taking multiple supplements for the past 4 weeks including acetyl-L-carnitine 1000 mg twice daily. The symptoms appeared 3 days after beginning to take acetyl-L-carnitine and worsened over the next week. The patient had increased speech rate and volume and reported increased energy levels and racing thoughts. The patient's parent reported irritability and an increase in loud behaviors at home, similar to a previous episode of mania. The patient was advised to discontinue acetyl-L-carnitine, and the manic symptoms disappeared 3 days later (95062).

Psychiatric ...Orally, acetyl-L-carnitine may cause agitation (restlessness and motor overactivity) (1596,1599,12743,13007). Side effects reported in people with Alzheimer disease include psychiatric disturbances such as depression, mania, confusion and aggression, but it is not clear whether these are due to acetyl-L-carnitine or the condition itself (1594,1595,1596,1597,1598,1599,9105,10391).

Other ...One of the metabolites of acetyl-L-carnitine can cause the urine, breath, and sweat to have a fishy odor (12756). Also, foul smelling urine has been reported following oral use of a combination of acetyl-L-carnitine and alpha-lipoic acid (90441).

(Read more about ACETYL-L-CARNITINE)

General ...Orally, alpha-GPC seems to be well tolerated.
Serious Adverse Effects (Rare):
Orally: Stroke.

Dermatologic ...Orally, some patients can experience skin rash (12102). Intramuscularly, alpha-GPC can cause erythema at the injection site (12101).

Gastrointestinal ...Orally, alpha-GPC has been rarely associated with diarrhea, heartburn, nausea, and vomiting (12102).
Intramuscularly, alpha-GPC has been rarely associated with diarrhea, heartburn, nausea, and vomiting (12102).

Neurologic/CNS ...Orally, alpha-GPC has been rarely associated with dizziness, excitation, headache, and insomnia (12102). Alpha-GPC use for at least 2 months has also been associated with an elevated risk of stroke when compared with non-users or those who used alpha-GPC for less than 2 months (108883).
Intramuscularly, alpha-GPC has been rarely associated with confusion, excitation, fainting, headache, and insomnia (12102).

(Read more about ALPHA-GPC)

General ...Orally, choline is well tolerated when used appropriately. Adverse effects have been reported with doses exceeding the tolerable upper intake level (UL) of 3.5 grams daily.
Most Common Adverse Effects:
Orally: Fishy body odor. At high doses of at least 9 grams daily, choline has been reported to cause diarrhea, nausea, salivation, sweating, and vomiting.

Cardiovascular ...Orally, doses of choline greater than 7. 5 grams daily may cause low blood pressure (94648).

Gastrointestinal ...Orally, large doses of choline can cause nausea, vomiting, salivation, and anorexia (42275,91231). Gastrointestinal discomfort has reportedly occurred with doses of 9 grams daily, while gastroenteritis has reportedly occurred with doses of 32 grams daily (42291,42310). Doses of lecithin 100 grams standardized to 3.5% choline have reportedly caused diarrhea and fecal incontinence (42312).

Genitourinary ...Orally, large doses of choline greater than 9 grams daily have been reported to cause urinary incontinence (42291).

Neurologic/CNS ...Orally, high intake of choline may cause sweating due to peripheral cholinergic effects (42275).

Oncologic ...In one population study, consuming large amounts of choline was associated with an increased risk of colorectal cancer in females, even after adjusting for red meat intake (14845). However, more research is needed to confirm this finding.

Psychiatric ...Orally, large doses of choline (9 grams daily) have been associated with onset of depression in patients taking neuroleptics. Further research is needed to clarify this finding (42270).

Other ...Orally, choline intake may cause a fishy body odor due to intestinal metabolism of choline to trimethylamine (42285,42275,42310,92111,92112).

(Read more about CHOLINE)

General ...Orally, folic acid is generally well-tolerated in amounts found in fortified foods, as well as in supplemental doses of less than 1 mg daily.
Most Common Adverse Effects:
Orally: At doses of 5 mg daily - abdominal cramps, diarrhea, and rash. At doses of 15 mg daily - bitter taste, confusion, hyperactivity, impaired judgment, irritability, nausea, sleep disturbances.
Serious Adverse Effects (Rare):
Orally: Cancer (long-term use), cardiovascular complications, liver injury, seizures.
All ROAs: Allergic reactions such as bronchospasm and anaphylactic shock.

Cardiovascular ...There is some concern that high oral doses of folic acid might increase the risk of adverse cardiovascular outcomes. Clinical research shows that taking doses of 800 mcg to 1.2 mg/day might increase the risk of adverse cardiovascular events in patients with cardiovascular disease (12150,13482). High doses of folic acid might promote cell growth by providing large amounts of the biochemical precursors needed for cell replication. Overgrowth of cells in the vascular wall might increase the risk of occlusion (12150). Although some research suggests that use of folic acid might increase the need for coronary revascularization, analysis of multiple studies suggests that taking folic acid up to 5 mg/day for up to 24 months does not appear to affect coronary revascularization risk (90798).

Dermatologic ...Orally, folic acid 1-5 mg daily can cause rash (7225,90375,91319). Folic acid 15 mg daily can sometimes cause allergic skin reactions (15).

Gastrointestinal ...Orally, folic acid 5 mg daily can cause abdominal cramps and diarrhea (7225). Folic acid 15 mg daily can sometimes cause nausea, abdominal distention, flatulence, and bitter taste in the mouth (15). In children aged 6-30 months at risk of malnourishment, taking a nutritional supplement (Nutriset Ltd) enriched in folic acid 75-150 mcg daily, with or without vitamin B 12 0.9-1.8 mcg daily, for 6 months increases the likelihood of having persistent diarrhea (90391).

Hepatic ...Liver dysfunction, with jaundice and very high liver enzymes, occurred in a 30-year-old pregnant patient with severe nausea and vomiting taking a folic acid supplement (Folic acid, Nature Made) 400 mcg daily. Based on the timing of ingestion, the lack of other etiological factors, a positive drug-induced lymphocyte stimulation test, and liver function normalization once the folic acid had been stopped, the authors suggest the folic acid supplement was the cause. However, the authors did not determine which substance in the folic acid supplement was responsible and therefore it cannot be determined that folic acid itself was the cause (91309).

Neurologic/CNS ...Orally, folic acid 15 mg daily can sometimes cause altered sleep patterns, vivid dreaming, irritability, excitability, hyperactivity, confusion, and impaired judgment (15). Large doses of folic acid can also precipitate or exacerbate neuropathy in people deficient in vitamin B12 (6243). Use of folic acid for undiagnosed anemia has masked the symptoms of pernicious anemia, resulting in lack of treatment and eventual neurological damage (15). Patients should be warned not to self-treat suspected anemia. There is also some concern that consuming high amounts of folic acid from the diet and/or supplements might worsen cognitive decline in older people. A large-scale study suggests that people over 65 years of age, who consume large amounts of folic acid (median of 742 mcg/day), have cognitive decline at a rate twice as fast as those consuming smaller amounts (median of 186 mcg/day). It's not known if this is directly attributable to folic acid. It is theorized that it could be due to folic acid masking a vitamin B12 deficiency. Vitamin B12 deficiency is associated with cognitive decline (13068). More evidence is needed to determine the significance of this finding. For now, suggest that most patients aim for the recommended folic acid intake of 400 mcg/day.

Oncologic ...There is some concern that high dose folic acid might increase the risk of cancer, although research is unclear and conflicting. A large-scale population study suggests that taking a multivitamin more than 7 times per week with a separate folic acid supplement significantly increased the risk of prostate cancer (15607). Clinical research also shows that taking folic acid 1 mg daily increase the absolute risk of prostate cancer by 6.4% over a 10-year period when compared with placebo. However, those with a higher baseline dietary intake of folic acid had a lower rate of prostate cancer, but this was not statistically significant. Also, folate and folic acid intake in patients with prostate cancer is not associated with the risk of prostate cancer recurrence after radical prostatectomy (91317). However, it is possible that discrepancies are due to dietary folate versus folic acid intake. Large analyses of population studies suggest that while dietary folate/folic acid is not associated with prostate cancer, high blood folate/folic acid increases the risk of prostate cancer (50411,91316).
Additional clinical research shows that taking folic acid 800 mcg daily, in combination with vitamin B12 400 mcg, significantly increases the risk of developing cancer, especially lung cancer, and all-cause mortality in patients with cardiovascular disease (17041). However, this may be due to vitamin B12, as other observational research found that higher vitamin B12 levels are linked with an increased risk for lung cancer (102383). Meta-analyses of large supplementation trials of folic acid at levels between 0.5-2.5 mg daily also suggest an increased risk of cancer (50497,110318). Also, in elderly individuals, taking folic acid 400 mcg daily with vitamin B12 500 mcg daily increased the risk of cancer. The risk was highest in individuals over 80 years of age and in females and mainly involved gastrointestinal and colorectal cancers (90393).
Not all researchers suspect that high intake of folic acid supplements might be harmful. Some research suggests that increased dietary intake of folic acid, along with other nutrients, might be protective against cancer (16822). A meta-analysis of multiple clinical trials suggests that folic acid supplementation studies with folic acid levels between 500 mcg to 50 mg/day does not increase the risk of general or site-specific cancer for up to 7 years (91312,91321). Also, a post-hoc subgroup analysis of results from clinical research in adults with a history of recent stroke or ischemic attack suggests that taking folic acid, vitamin B12, and vitamin B6 does not increase cancer risk overall, although it was associated with an increased risk of cancer in patients who also had diabetes (90378).

Psychiatric ...Orally, folic acid 15 mg daily can sometimes cause exacerbation of seizure frequency and psychotic behavior (15).

Pulmonary/Respiratory ...Folic acid use in late pregnancy has been associated with an increased risk of persistent and childhood asthma at 3. 5 years in population research (50380). When taken pre-pregnancy or early in pregnancy, population research has not found an association with increased risk of asthma or allergies in childhood (90799,103979). Folic acid use in pregnancy has been associated with a slightly increased risk of wheeze and lower respiratory tract infections up to 18 months of age in population research (50328).

(Read more about FOLIC ACID)

General ...Orally, niacin is well tolerated in the amounts found in foods. It is also generally well tolerated in prescription doses when monitored by a healthcare provider.
Most Common Adverse Effects:
Orally: Flushing, gastrointestinal complaints (abdominal pain, constipation, diarrhea, heartburn, nausea, vomiting), and elevated liver enzymes.
Serious Adverse Effects (Rare):
Orally: Hepatotoxicity, myopathy, thrombocytopenia, and vision changes.

Cardiovascular ...Orally, flushing is a common dose-related adverse reaction to niacin. A large meta-analysis of clinical studies shows that up to 70% of patients may experience flushing (96211). Although flushing can occur with doses of niacin as low as 30 mg daily, it is more common with the larger doses used for treatment of dyslipidemia. The flushing reaction is due to prostaglandin-induced blood vessel dilation and can also include symptoms of burning, tingling, urticaria, erythema, pain, and itching of the face, arms, and chest. There may also be increased intracranial blood flow and headache (4889,26089,93341,104933). Onset is highly variable and ranges from within 30 minutes to as long as 6 weeks after the initial dose (6243). Flushing can be minimized via various strategies, including taking doses with meals, slow dose titration, using extended release formulations, pretreating with non-steroidal anti-inflammatory drugs, taking regular-release niacin with meals, or taking the sustained-release product at bedtime (4852,4853,4854,4857,4858,25922,26073,26084). Flushing often diminishes with continued use but can recur when niacin is restarted after missed doses (4863,6243,26081). The vasodilating effects of niacin can also cause hypotension, dizziness, tachycardia, arrhythmias, syncope, and vasovagal attacks, especially in patients who are already taking antihypertensive drugs (4863,12033,93341,110494).
High doses of niacin can raise homocysteine levels. A 17% increase has been reported with 1 gram daily and a 55% increased has been reported with 3 grams daily. Elevated homocysteine levels are an independent risk factor for cardiovascular disease (490); however, the clinical significance of this effect is unknown. A large-scale study (AIM-HIGH) found that patients receiving extended-release niacin (Niaspan) 1500-2000 mg daily with a statin had an over two-fold increased risk of ischemic stroke (1.6%) when compared with those receiving only simvastatin (0.7%). However, when the risk was adjusted for confounding factors, niacin was not found to be associated with increased stroke risk (17627,93354). A meta-analysis of three clinical trials conducted in approximately 29,000 patients showed a higher risk of mortality in patients taking niacin in addition to a statin when compared with a statin alone. However, with a p-value of 0.05 and confidence interval including 1, the validity of this finding remains unclear (97308).

Endocrine ...Orally, niacin can impair glucose tolerance in a dose-dependent manner. Dosages of 3-4 grams daily appear to increase blood glucose in patients with or without diabetes, while dosages of 1.5 grams daily or less have minimal effects (12033). Niacin is thought to impair glucose tolerance by increasing insulin resistance or increasing hepatic output of glucose (4863,11692,11693). In patients with diabetes, niacin 4.5 grams daily for 5 weeks has been associated with an average 16% increase in plasma glucose and 21% increase in glycated hemoglobin (HbA1C) (4860). Up to 35% of patients with diabetes may need to increase the dose or number of hypoglycemic agents when niacin is started (4458,4860,4863,11689,12033). Occasionally, severe hyperglycemia requiring hospitalization can occur (11693). In patients with impaired fasting glucose levels, niacin may also increase fasting blood glucose, and adding colesevelam might attenuate this effect (93343).
Although patients without diabetes seem to only experience small and clinically insignificant increases in glucose (4458), niacin might increase their risk of developing diabetes. A meta-analysis of clinical research involving over 26,000 patients shows that using niacin over 5 years is associated with increased prevalence of new onset type 2 diabetes at a rate of 1 additional case of diabetes for every 43 patients treated with niacin (96207). This finding is limited because the individual trials were not designed to assess diabetes risk and the analysis could not be adjusted for confounding factors like obesity. One small clinical study shows that taking extended-release niacin with ezetimibe/simvastatin does not increase the risk of a new diagnosis of diabetes or need for antidiabetic medication when compared with ezetimibe/simvastatin alone after 16 months (93344). This may indicate that the increased risk of developing diabetes is associated with niacin use for more than 16 months.
Niacin therapy has also been linked with hypothyroidism and its associated alterations in thyroid hormone and binding globulin tests (such as decreased total serum thyroxine, increased triiodothyronine, decreased thyroxine-binding globulin levels, and increased triiodothyronine uptake) (25916,25925,25926,25928).

Gastrointestinal ...Orally, large doses of niacin can cause gastrointestinal disturbances including nausea, vomiting, bloating, heartburn, abdominal pain, anorexia, diarrhea, constipation, and activation of peptic ulcers (4458,4863,12033,26083,93341,96211). These effects may be reduced by taking the drug with meals or antacid, and usually disappear within two weeks of continued therapy (4851,26094). Gastrointestinal effects may be more common with time-release preparations of niacin (11691).

Hematologic ...Orally, sustained-release niacin has been associated with cases of reversible coagulopathy, mild eosinophilia, and decreased platelet counts (4818,25915,26097,93340). Also, there have been reports of patients who developed leukopenia while taking niacin for the treatment of hypercholesterolemia (25916).

Hepatic ...Orally, niacin is associated with elevated liver function tests and jaundice, especially with doses of 3 grams/day or more, and when doses are rapidly increased (4458,4863,6243). The risk of hepatotoxicity appears to be higher with slow-release and extended-release products (4855,4856,4863,6243,11691,12026,12033,93342). Niacin should be discontinued if liver function tests rise to three times the upper limit of normal (4863). There are rare cases of severe hepatotoxicity with fulminant hepatitis and encephalopathy due to niacin (4863,6243,11691). Also, there is at least one case of niacin-induced coagulopathy resulting from liver injury without liver enzyme changes (93340).

Musculoskeletal ...Orally, niacin has been associated with elevated creatine kinase levels (4818,4888). Also, several cases of niacin-induced myopathy have been reported (26100,26111). Concomitant administration of niacin and HMG-CoA reductase inhibitors may increase the risk of myopathy and rhabdomyolysis (14508,25918,26111); patients should be monitored closely.

Neurologic/CNS ...Orally, high-dose niacin has been associated with cases of neuropsychiatric adverse events such as extreme pain and psychosis. Two 65-year-old males taking niacin orally for 5 months for the treatment of dyslipidemias developed severe dental and gingival pain. The pain was relieved by the discontinuation of niacin. The pain was thought to be due to inflammation and pain referral to the teeth (4862). In one case report, a 52-year-old male with no history of psychiatric illness who initially complained of hot flushes when taking niacin 500 mg daily, presented with an acute psychotic episode involving mania after niacin was increased to 1000 mg daily (93350).

Ocular/Otic ...Orally, chronic use of large amounts of niacin has been associated with dry eyes, toxic amblyopia, blurred vision, eyelid swelling, eyelid discoloration, loss of eyebrows and eyelashes, proptosis, keratitis, macular edema, and cystic maculopathy, which appear to be dose-dependent and reversible (4863,6243,26112).

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General ...Orally, phosphatidylserine is generally well tolerated.
Most Common Adverse Effects:
Orally: Flatulence, gastrointestinal upset, headache, insomnia, and nausea.

Gastrointestinal ...Orally, phosphatidylserine can cause gastrointestinal upset such as flatulence or nausea. Gastrointestinal upset can occur at doses of 200-300 mg/day (7116,7121,15539,68862,90711).

Neurologic/CNS ...Orally, phosphatidylserine can cause insomnia. Insomnia is more likely to occur with a higher dose of 600 mg (7121,68844). Headache has also been reported (90711).

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General ...Orally, tyrosine seems to be well tolerated. No serious adverse effects have been documented; however, a thorough evaluation of safety outcomes has not been conducted.
Most Common Adverse Effects:
Orally: Fatigue, headache, heartburn, and nausea.

Gastrointestinal ...Orally, tyrosine can cause nausea and heartburn when taken at a dose of 150 mg/kg (7211). Taking tyrosine 4 grams daily in combination with 5-hydroxytryptophan 800 mg and carbidopa 100 mg can cause diarrhea, nausea, and vomiting. These effects can be mitigated by lowering the dosage (918).

Musculoskeletal ...Orally, larger doses of tyrosine (150 mg/kg) can cause arthralgia, but this is uncommon (7211).

Neurologic/CNS ...Orally, larger doses of tyrosine (150 mg/kg) can cause headache and fatigue (7211). Taking a combination of tyrosine 4 grams, 5-hydroxytryptophan 800 mg, and carbidopa 100 mg can cause drowsiness and agitation. These effects can be mitigated by lowering the dosage (918).

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General ...Orally, intramuscularly, and topically, vitamin B12 is generally well-tolerated.
Most Common Adverse Effects:
Intramuscular: Injection site reactions.
Serious Adverse Effects (Rare):
Intramuscularly: Severe hypokalemia has been rarely linked with correction of megaloblastic anemia with vitamin B12.

Cardiovascular ...In human clinical research, an intravenous loading dose of folic acid, vitamin B6, and vitamin B12, followed by daily oral administration after coronary stenting, increased restenosis rates (12150). Hypertension following intravenous administration of hydroxocobalamin has been reported in human research (82870,82864).

Dermatologic ...Orally or intramuscularly, vitamin B12 can cause allergic reactions such as rash, pruritus, erythema, and urticaria. Theoretically, allergic reactions might be caused by the cobalt within the vitamin B12 molecule (82864,90373,90381,103974). In one case report, oral methylcobalamin resulted in contact dermatitis in a 59-year-old Japanese female with a cobalt allergy (103974). In another case report, a 69-year-old female developed a symmetrical erythematous-squamous rash for 5 years after oral vitamin B12 supplementation for 10 years. A patch test confirmed that the systemic allergic dermatitis was due to vitamin B12 supplementation, which resolved 3 months after discontinuation (114578).
Vitamin B12 (intramuscular or oral) has also been associated with at least 19 cases of acneiform eruptions which resolved upon discontinuation of vitamin B12 (90365,90369,90388). High-dose vitamin B12 (20 mcg daily) and vitamin B6 (80 mg daily) have been associated with cases of rosacea fulminans characterized by intense erythema with nodules, papules, and pustules. Symptoms may last up to four months after the supplement is stopped and can be treated with systemic corticosteroids and topical therapy (10998,82870,82871).

Gastrointestinal ...Intravenously, vitamin B12 (hydroxocobalamin) 2. 5-10 grams can cause nausea and dysphagia (82864).

Genitourinary ...Intravenously, vitamin B12 (hydroxocobalamin) 5-15 grams has been associated with chromaturia in clinical research (82870,82871,112282,112264).

Hematologic ...According to case report data, the correction of megaloblastic anemia with vitamin B12 may result in fatal hypokalemia (82914).

Musculoskeletal ...According to case report data, correction of megaloblastic anemia with vitamin B12 has precipitated gout in susceptible individuals (82879).

Neurologic/CNS ...Treatment with vitamin B12 has been rarely associated with involuntary movements in infants with vitamin B12 deficiency (90370,90385,90397). In some cases these adverse reactions were misdiagnosed as seizures or infantile tremor syndrome (90370,90385). These adverse reactions presented 2-5 days after treatment with vitamin B12 and resolved once vitamin B12 was discontinued (90370,90385,90397).

Oncologic ...Although some epidemiological research disagrees (9454), most research has found that elevated plasma levels of vitamin B12 are associated with an increased risk of various types of cancer, including lung and prostate cancers and solid tumors (50411,102383,107743). One study found, when compared with blood levels of vitamin B12 less than 1000 ng/mL, plasma vitamin B12 levels of at least 1000 ng/mL was strongly associated with the occurrence of solid cancer (107743). It is unclear if increased intake of vitamin B12, either through the diet or supplementation, directly affects the risk of cancer. It is possible that having cancer increases the risk of vitamin B12 elevation. However, one observational study has found that the highest quintile of dietary intake of vitamin B12 is associated with a 75% increased incidence of developing esophageal cancer when compared with the lowest quintile in never drinkers, but not drinkers (107147).

Renal ...There is a case report of oxalate nephropathy in a 54-year-old male which was determined to be related to the use of intravenous hydroxocobalamin as treatment for cyanide poisoning. Intermittent hemodialysis was started 5 days after admission, along with a low-oxalate diet, oral calcium acetate, and pyridoxine 5 mg/kg daily (107148). A review of the use of intravenous hydroxocobalamin for suspected cyanide poisoning in 21 intensive care units in France between 2011 and 2017 resulted in a 60% increased odds of acute kidney injury and a 77% increased odds of severe acute kidney injury in the first week. However, biopsies were not conducted and a direct link with use of hydroxocobalamin could not be made (107139).

Other ...Several studies have found that higher vitamin B12 levels may be associated with increased mortality or decreased survival rates in hospitalized elderly patients (82889,82812,82857,82895). Human research has also found a positive correlation between vitamin B12 status and all-cause mortality in Pima Indians with diabetes (82863).

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General ...Orally or by injection, vitamin B6 is well tolerated in doses less than 100 mg daily.
Most Common Adverse Effects:
Orally or by injection: Abdominal pain, allergic reactions, headache, heartburn, loss of appetite, nausea, somnolence, vomiting.
Serious Adverse Effects (Rare):
Orally or by injection: Sensory neuropathy (high doses).

Dermatologic ...Orally, vitamin B6 (pyridoxine) has been linked to reports of skin and other allergic reactions and photosensitivity (8195,9479,90375). High-dose vitamin B6 (80 mg daily as pyridoxine) and vitamin B12 (20 mcg daily) have been associated with cases of rosacea fulminans characterized by intense erythema with nodules, papules, and pustules. Symptoms may persist for up to 4 months after the supplement is stopped, and may require treatment with systemic corticosteroids and topical therapy (10998).

Gastrointestinal ...Orally or by injection, vitamin B6 (pyridoxine) can cause nausea, vomiting, heartburn, abdominal pain, mild diarrhea, and loss of appetite (8195,9479,16306,83064,83103,107124,107127,107135). In a clinical trial, one patient experienced infectious gastroenteritis that was deemed possibly related to taking vitamin B6 (pyridoxine) orally up to 20 mg/kg daily (90796). One small case-control study has raised concern that long-term dietary vitamin B6 intake in amounts ranging from 3.56-6.59 mg daily can increase the risk of ulcerative colitis (3350).

Hematologic ...Orally or by injection, vitamin B6 (pyridoxine) can cause decreased serum folic acid concentrations (8195,9479). One case of persistent bleeding of unknown origin has been reported in a clinical trial for a patient who used vitamin B6 (pyridoxine) 100 mg twice daily on days 16 to 35 of the menstrual cycle (83103). It is unclear if this effect was due to vitamin B6 intake.

Musculoskeletal ...Orally or by injection, vitamin B6 (pyridoxine) can cause breast soreness or enlargement (8195).

Neurologic/CNS ...Orally or by injection, vitamin B6 (pyridoxine) can cause headache, paresthesia, and somnolence (8195,9479,16306). Vitamin B6 (pyridoxine) can also cause sensory neuropathy, which is related to daily dose and duration of intake. Doses exceeding 1000 mg daily or total doses of 1000 grams or more pose the most risk, although neuropathy can occur with lower daily or total doses as well (8195). The mechanism of the neurotoxicity is unknown, but is thought to occur when the liver's capacity to phosphorylate pyridoxine via the active coenzyme pyridoxal phosphate is exceeded (8204). Some researchers recommend taking vitamin B6 as pyridoxal phosphate to avoid pyridoxine neuropathy, but its safety is unknown (8204). Vitamin B6 (pyridoxine) neuropathy is characterized by numbness and impairment of the sense of position and vibration of the distal limbs, and a gradual progressive sensory ataxia (8196,10439). The syndrome is usually reversible with discontinuation of pyridoxine at the first appearance of neurologic symptoms. Residual symptoms have been reported in patients taking more than 2 grams daily for extended periods (8195,8196). Tell patients daily doses of 100 mg or less are unlikely to cause problems (3094).

Oncologic ...In females, population research has found that a median intake of vitamin B6 1. 63 mg daily is associated with a 3.6-fold increased risk of rectal cancer when compared with a median intake of 1.05 mg daily (83024). A post-hoc subgroup analysis of results from clinical research in adults with a history of recent stroke or ischemic attack suggests that taking folic acid, vitamin B12, and vitamin B6 does not increase cancer risk overall, although it was associated with an increased risk of cancer in patients who also had diabetes (90378). Also, in patients with nasopharyngeal carcinoma, population research has found that consuming at least 8.6 mg daily of supplemental vitamin B6 during treatment was associated with a lower overall survival rate over 5 years, as well as a reduced progression-free survival, when compared with non-users and those with intakes of up to 8.6 mg daily (107134).

(Read more about VITAMIN B6)