Is Cortisol useful for sleep?

Cortisol follows a strong circadian rhythm: levels peak in the morning to promote wakefulness and decline in the evening to allow sleep onset. A disrupted cortisol pattern – due to chronic stress, shift work, or inflammation – can impair sleep quality. Cortisol itself is not 'useful' for sleep; rather, a normal daily cortisol curve is a prerequisite for healthy sleep. Persistently high evening cortisol is associated with insomnia and lighter sleep. This knowledge comes from endocrine and sleep physiology, not from consumer DNA or microbiome tests. MyBody-X reports do not measure cortisol directly. For sleep issues, focus on stress reduction, sleep hygiene, and medical evaluation if needed. Evidence grade: mechanistic – well-established physiology, but not supported by the provided context.