What role does LCT play in longevity?

The LCT gene encodes lactase, the enzyme that breaks down lactose in dairy. A common SNP (rs4988235) determines adult lactose tolerance. Direct evidence linking LCT to longevity is weak. Some observational studies suggest that lactose-tolerant individuals consume more dairy, which may benefit bone health and vitamin D status – factors that could modestly influence lifespan. However, effect sizes are small, confounded by lifestyle and ancestry, and no robust longevity association has been replicated. Mechanistically, LCT is not a core longevity gene. The evidence grade is 'mechanistic/unclear'. A DNA test for LCT can guide personalized nutrition (e.g., avoiding lactose if intolerant) but should not be marketed as a longevity predictor. Caveat: No direct lifespan studies in the provided context.