Evidence check: FTO in the context of sleep

The link between FTO variants and sleep is less clear than the well-established association with BMI and obesity. Some GWAS studies (e.g., on sleep duration or chronotype) have identified FTO as one of many loci, but with very small effect sizes. Most of these associations disappear or are greatly attenuated after adjusting for BMI, suggesting that the effect on sleep may be mediated indirectly through body composition. There are no robust intervention studies showing that FTO variants directly affect sleep quality or architecture. Consumer DNA tests tend to overstate such connections. In practice, an FTO risk allele should not be used as a sole explanation for sleep issues. Lifestyle factors (diet, exercise, sleep hygiene) have a far greater impact. Evidence: human-moderate (GWAS, but small effects and possible confounding).