What to watch with Cortisol and sleep?

Cortisol and sleep are tightly linked: cortisol follows a circadian rhythm with peaks in the morning and troughs at night. Sleep deprivation or disruption can shift this rhythm, leading to elevated evening cortisol, which further impairs sleep quality. Genetic variants like COMT rs4680 (Val158Met) affect dopamine breakdown and indirectly stress response, but the effect on cortisol is small and not diagnostic. Consumer DNA tests do not measure cortisol directly. Focus on sleep hygiene: consistent bedtimes, reduced screen time, and avoiding caffeine in the evening. For persistent sleep issues or stress symptoms, clinical evaluation (e.g., salivary cortisol day profile) is recommended. The evidence for the cortisol-sleep link is solid (human-moderate), while the genetic component is weak and not suitable for individual prediction.