Evidence check: LCT in the context of longevity

The LCT gene encodes lactase, the enzyme needed to digest lactose, the sugar in milk. Variants such as rs4988235 determine whether an individual maintains lactase production into adulthood (lactase persistence) or becomes lactose intolerant. In the context of longevity, direct evidence linking LCT variants to lifespan is weak. Some observational studies have associated dairy consumption with reduced mortality, but results are inconsistent and confounded by lifestyle, diet, and socioeconomic factors. The effect of lactase persistence on health is indirect: it allows dairy intake, which provides calcium, vitamin D, and protein, but also saturated fats. Genome-wide association studies (GWAS) on longevity occasionally include LCT, but effect sizes are tiny and not consistently replicated. Therefore, interpreting LCT genotype alone for longevity is not evidence-based. A balanced diet and healthy lifestyle are far more influential. For those with lactose intolerance, lactose-free alternatives or supplements can be used without expected harm to longevity. The evidence is moderate, based on observational data; no randomized trials demonstrate a causal effect.