Evidence check: LCT in the context of sleep

The link between the LCT gene (lactase) and sleep lacks direct scientific evidence. LCT encodes lactase, the enzyme digesting lactose. Variants like rs4988235 determine lactase persistence in adults. No robust GWAS or interventional studies demonstrate a direct effect of LCT variants on sleep quality, duration, or architecture. Indirect effects are conceivable: lactose intolerance may cause bloating or abdominal discomfort that disturbs sleep, but this is symptom-mediated, not a direct genetic pathway. Additionally, milk is often recommended as a sleep aid (due to tryptophan), but lactose digestion genetics are irrelevant here. The evidence is therefore rated as 'unclear'. Consumer DNA tests provide no clinically actionable sleep information from LCT. For sleep issues, focus on stress, sleep hygiene, and medical evaluation.