What to watch with B12 and longevity?

The question of B12 and longevity is complex and often overhyped by marketing. Vitamin B12 is an essential cofactor for DNA synthesis, nerve myelination, and especially the methylation cycle – together with folate (or methylfolate) and the MTHFR enzyme. An MTHFR variant (as mentioned in the context) can slightly impair the conversion of folic acid to active methylfolate, theoretically increasing the need for methylfolate and B12. However, the effect of single SNPs is usually small and often overstated in direct-to-consumer tests. For longevity, there is no robust evidence that high-dose B12 extends lifespan. Associations between B12 status and longevity are mostly observational and confounded by factors like kidney function or inflammation. The FOXO3 gene (rs2802292), in contrast, shows reproducible, albeit modest, effects on human lifespan – independent of B12. Practically: if a deficiency is confirmed by blood test, supplementation is warranted, but blanket high dosing without deficiency is not evidence-based. Watch for interactions with medications (e.g., metformin, proton pump inhibitors) and measure B12 levels before supplementing. The evidence for B12 as a longevity elixir is weak; focus on a balanced diet with B12 sources (meat, fish, eggs, fortified products) is advisable.