Vitamin B12

Vitamin B12 is commonly taken to improve cognitive function or to supplement dietary deficiencies. To evaluate whether vitamin B12 supplementation is actually needed, we reviewed the literature for impacts on cognitive function. We combine this review with deficiency rates and our knowledge of deficiency symptoms. In general, we reserve vitamin B12 supplementation for those that can't get it in their diet.

For background, vitamin B12 is an essential vitamin involved in the healthy function of the central nervous system, DNA, and red blood cells. It is primarily found in meat and foods of animal origin such as eggs and milk. Because vitamin B12 is found primarily in animal-based sources, vegans and some vegetarians have an higher risk of being deficient in this vitamin. Seeking vitamin B12 sources is important, as Vitamin B12 deficiency is serious and leads to neurologic issues, dementia, anemia, weakened immune system, weight loss, fatigue, and infertility.

However, for otherwise healthy individuals, a systematic review of 16 randomized trials found that supplementation with B12 has no impact on cognitive function.¹ B12 supplementation in individuals with dementia and low B12 levels also showed no improvement in cognitive function in a review of 3 eligible studies.² Overall, the evidence of B12 being a brain booster is weak.

Given the limited evidence for cognitive function improvement, we reserve B12 for the primary use of avoiding deficiencies. That is, we recommend B12 primarily for vegans who don't have access to animal by-products and for vegetarians who don't eat many animal by-products.