B vitamins are important for cell metabolism. Vitamins B6 (pyridoxine), B9 (folic acid), and B12 (cobalamin) can also reduce levels of the amino acid homocysteine. Homocysteine levels are commonly high in people over 65 and are linked to strokes, coronary artery disease, and dementia. In clinical trials, vitamin B supplements did not improve cognition but other trials suggest they may protect against cognitive decline in people with high homocysteine levels. At recomended doses, vitamin B supplements are generally safe.
Multiple meta-analyses and systematic reviews have examined the cognitive effects of vitamin B supplementation, but the outcomes vary depending on baseline cognitive status and homocysteine levels. Our search found:
• 8 meta-analyses of numerous clinical trials examining the effects of B vitamin supplementation on cognitive function • 4 meta-analyses of numerous observational studies examining the links between homocysteine levels, B vitamin levels, cognitive decline, and dementia • 1 randomized controlled study in patients with mild cognitive impairment • Numerous preclinical studies
B vitamin supplements will not improve cognition in most adults [1][2], but it may protect from cognitive decline in some high risk groups. High homocysteine levels have been consistently associated with dementia risk [3][4], and a randomized controlled trial suggests that B vitamin supplementation slows cognitive decline in select groups, including people with mild cognitive impairment and high baseline homocysteine levels [5-7][12][13]. A large meta-analysis did show that while B vitamins lowered homocysteine levels, they did not affect cognitive function [1]. But, the results were questioned due to the lack of people experiencing cognitive decline in the trials and other factors [8-11].
The evidence is mixed on whether B vitamins selectively affect APOE4 carriers versus non-carriers. Two cross-sectional epidemiological studies reported that high homocysteine levels are associated with worse cognitive function for APOE4 carriers, but not non-carriers, suggesting that APOE4 carriers are more likely to benefit from homocysteine-lowering B vitamins [14][15]. However, at least three other observational studies [16-18] report little to no interaction between APOE genotype and vitamin B12 in terms of cognitive function or dementia risk. For more information on what the APOE4 gene allele means for your health, read our APOE4 information page.
Although moderate beneficial effects on memory have been reported for patients with mild cognitive impairment, particularly in people with high baseline homocysteine levels [5][6], no benefits have been reported for Alzheimer's disease patients in clinical trials [6][19].
Vitamin B supplements are considered safe for most healthy people when taken at recommended doses, though drug interactions are possible. High folic acid levels can mask the anemia symptoms of vitamin B12 deficiency, which can delay diagnosis and increase the risk for serious long-term harm such as severe anemia and neurologic disturbances, including dementia. While some studies detected a relationship between folic acid intake and changes in cancer risk [20], a meta-analysis of clinical trials concluded folic acid neither increases nor decreases cancer incidence [21].
NOTE: This is not a comprehensive safety evaluation or complete list of potentially harmful drug interactions. It is important to discuss safety issues with your physician before taking any new supplement or medication.
B vitamins are available over the counter as pills, chewable tablets, extended release capsules, and in liquid form. In clinical trials, daily supplementation with 20 mg of vitamin B6, 0.5-5.0 mg of folic acid, and 0.5 mg of vitamin B12 reduced homocysteine levels. However, appropriate doses depend on a person’s age, dietary intake, and baseline levels of B vitamins. The ability to absorb vitamin B12 from the gut can become impaired for some people, particularly the elderly [22], leading to serious B12 deficiencies that must be clinically treated often with injections or high doses of oral B12 therapy.
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Vitamin B6: Fact Sheet for Consumers, National Institutes of Health, Office of Dietary Supplements
Vitamin B12: Fact Sheet for Consumers, National Institutes of Health, Office of Dietary Supplements
Folate: Fact Sheet for Consumers, National Institutes of Health, Office of Dietary Supplements
United States Pharmacopeial Convention (USP), ConsumerLab, and FDA Information on Dietary Supplements provide information on B vitamin supplements.
Check for drug-drug and drug-supplement interactions on Drugs.com