Vitamin B12 (Cobalamin) for Cognitive Function

Research suggests that the relationship between vitamin B12 and cognitive function is modest and context-dependent, with the clearest signals emerging in specific populations such as older adults with elevated homocysteine levels or people with type 2 diabetes taking metformin, where observational data indicate associations between sufficient B12 status and better cognitive performance. Two Cochrane systematic reviews of randomized controlled trials found that folic acid supplementation combined with vitamin B12 reliably lowered homocysteine levels but did not consistently translate into measurable cognitive improvements in unselected older adults, though one included trial did observe memory and processing speed benefits in a subgroup with high baseline homocysteine. Additional observational and cross-sectional studies point to possible sex-specific differences in how B12 levels relate to dementia risk, and newer metabolomic and genetic research is refining how deficiency is detected and understood at a biological level, though these findings do not yet speak directly to supplementation outcomes. Overall, the evidence base is limited by small sample sizes, heterogeneous populations, and a reliance on study designs that cannot establish causation, leaving the question of whether B12 supplementation meaningfully protects cognitive function in the general population unresolved.