What role does Cortisol play in Schlaf?

Cortisol, a glucocorticoid hormone from the adrenal cortex, follows a distinct circadian rhythm: it peaks in the early morning (cortisol awakening response) and declines throughout the day, reaching its nadir around midnight. This rhythm is crucial for regulating the sleep-wake cycle. Elevated cortisol levels in the evening or during the night can disrupt sleep architecture, reducing slow-wave sleep and increasing nighttime awakenings. Chronic stress, leading to sustained high cortisol, is strongly linked to insomnia and poor sleep quality. Conversely, restorative sleep helps maintain normal cortisol regulation. The evidence is robust from human studies, though individual variability exists due to genetics and lifestyle. Consumer tests like MyBody-X do not measure cortisol dynamics directly; they may offer indirect insights via stress-related SNPs, but these are not diagnostic. For persistent sleep issues, clinical assessment is recommended.