Is Vitamin D 25-OH useful for longevity?

Whether vitamin D (25-OH) is useful for longevity is not definitively answered by current science. Vitamin D is critical for bone health, immune regulation, and inflammation control—all processes linked to healthy aging. Observational studies consistently associate low 25-OH levels with higher all-cause mortality, especially in older adults. However, randomized controlled trials (RCTs) have not shown that supplementing vitamin D in people with adequate levels extends lifespan. The evidence is moderate at best, largely from observational and mechanistic data; causal longevity benefits remain unproven. High-dose supplementation carries risks (hypercalcemia, kidney stones). Practical takeaway: correcting a deficiency is evidence-based, but megadosing for longevity is not supported. The effect likely depends on baseline status, genetics, and lifestyle. Overall, vitamin D is a marker of health rather than a direct longevity agent.