How are CLOCK and sleep related?

The CLOCK gene (Circadian Locomotor Output Cycles Kaput) is a core component of the human circadian clock, interacting with BMAL1, PER, and CRY to regulate 24-hour sleep-wake cycles, hormone secretion, and metabolism. Variants in CLOCK, especially rs1801260 (T3111C), have been associated in candidate gene and GWAS studies with sleep duration, sleep onset latency, and daytime sleepiness. However, effect sizes are small and often not replicated across populations. Evidence level: human-moderate (observational/GWAS). A direct-to-consumer DNA test result for a CLOCK SNP does not provide actionable information for sleep optimization. Sleep is influenced by light exposure, lifestyle, stress, and many other genes. Therefore, relying on such a test for sleep advice is not evidence-based. For persistent sleep issues, clinical evaluation (sleep diary, actigraphy, polysomnography) is far more informative than a single genetic variant.