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Cortisol Diurnal Rhythm

Meaning

The Cortisol Diurnal Rhythm describes the predictable, cyclical pattern of cortisol secretion by the adrenal cortex over a 24-hour period, which is a critical component of the body’s circadian system. Under normal physiological conditions, cortisol levels peak shortly after waking to mobilize energy and prepare the body for the day’s demands, then gradually decline throughout the day, reaching their nadir around midnight. This rhythmic fluctuation is essential for regulating sleep-wake cycles, metabolism, immune function, and the overall stress response. Clinically assessing this rhythm, often through multiple salivary measurements, provides a nuanced view of HPA axis function.