What to watch with Vitamin D 25-OH and longevity?

Vitamin D (25-OH) is frequently discussed in the context of longevity, but the evidence is largely observational and not causal. Optimal 25-OH levels (e.g., 50–80 nmol/L) are associated with lower all-cause mortality, yet randomized trials have not shown a clear benefit from supplementation in replete individuals. Genetic variants in VDR, GC, or CYP2R1 can influence vitamin D metabolism, but their effect on longevity is small. Caution: very high levels (>125 nmol/L) may be toxic. A MyBody-X test can measure your 25-OH level, but interpretation should always consider lifestyle, sun exposure, and kidney function. Evidence: human-moderate (observational studies).