Is B12 useful for longevity?

Whether vitamin B12 is useful for longevity requires a nuanced, evidence-based answer. B12 is essential for DNA synthesis, nerve myelination, and homocysteine metabolism. Deficiency – common in vegans, older adults, and those with malabsorption (e.g., pernicious anemia, gastric bypass) – leads to elevated homocysteine, cognitive decline, and increased cardiovascular risk. Observational studies link low B12 status with accelerated aging and frailty, but randomized controlled trials directly testing B12 supplementation for lifespan extension are lacking. Thus, the evidence is 'human-moderate': sufficient to support healthspan relevance, but insufficient to claim longevity extension. Correcting a deficiency is clearly beneficial, but supraphysiological doses in replete individuals offer no proven advantage. Consumer DNA tests like MyBody-X do not measure B12 levels; they analyze genetic variants (e.g., MTHFR, FUT2) that modestly influence B12 metabolism. These effects are small and not diagnostic. For accurate assessment, blood biomarkers (holotranscobalamin, homocysteine) are required. Marketing claims portraying B12 as a 'longevity miracle' should be viewed skeptically.