Is CLOCK useful for sleep?

The CLOCK gene is a core component of the circadian clock and has been linked to sleep timing and chronotype in GWAS. However, effect sizes are small, and genetic testing for CLOCK variants does not provide actionable guidance for improving sleep in most individuals. Lifestyle factors such as light exposure, meal timing, and sleep hygiene have a much larger impact. Evidence is rated as 'human-moderate' because associations are replicated but not clinically validated for intervention. Consumer DNA tests often overstate the relevance of single SNPs. For sleep issues, a sleep diary or actigraphy is more informative than a CLOCK gene test.