What role does Vitamin D 25-OH play in longevity?

Vitamin D 25-OH (25-hydroxyvitamin D) is a key biomarker for vitamin D status and is associated with several health outcomes that may influence longevity. Observational studies consistently link low 25-OH-D levels with increased all-cause mortality, cardiovascular disease, certain cancers, and infections. However, large randomized controlled trials (e.g., VITAL) have not demonstrated a clear causal benefit of vitamin D supplementation on lifespan in generally healthy populations. The evidence is thus moderate and largely associative. Excessively high levels can be toxic (hypercalcemia). Optimal levels are typically 50–80 nmol/L, but individual factors such as genetics (e.g., VDR polymorphisms), sun exposure, and kidney function modulate requirements. Direct longevity effects remain unproven; vitamin D status is better viewed as a marker of overall health rather than a direct longevity intervention. Caution: supplementation without medical guidance may cause harm at high doses.