Can B12 help with longevity?

Based on the provided context, there is no direct evidence that vitamin B12 supplementation extends longevity. B12 is crucial for red blood cell formation, neurological function, and DNA synthesis. Deficiency can cause fatigue and cognitive decline, which may indirectly affect healthspan. The context mentions a FUT2 gene variant (rs602662) associated with B12 levels, but no link to longevity is established. Consumer DNA tests may report such variants, but their effect sizes are small and clinical relevance for longevity is unclear. While adequate B12 is essential for overall health, claims that it directly prolongs lifespan are not supported by the given knowledge. Evidence is weak/unclear. Always address deficiencies first; megadosing for longevity lacks robust human evidence.