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Diurnal Cortisol Cycle

Meaning

The Diurnal Cortisol Cycle is the predictable, 24-hour rhythmic fluctuation of the stress hormone cortisol, serving as a core component of the body’s circadian system and metabolic preparedness. This cycle is characterized by the Cortisol Awakening Response (CAR), a sharp rise in cortisol immediately upon waking, followed by a steady decline throughout the day and the lowest point near midnight. The cycle’s integrity is a direct biomarker for the resilience and function of the hypothalamic-pituitary-adrenal (HPA) axis, with an optimized cycle supporting sustained energy and robust stress adaptation. Dysfunction in this cycle is often implicated in chronic fatigue and immune dysregulation.