What is the Origin of Morning Cortisol Peak?

This concept is central to clinical endocrinology and stress physiology, with the CAR being one of the most studied and reliable biomarkers of HPA axis function. The mechanism is a proactive, feed-forward response, not merely a reaction to immediate stressors. Its measurement is a standard procedure in functional hormone testing, providing insight into adrenal reserve and stress adaptation capacity.

What is the Mechanism of Morning Cortisol Peak?

The peak is orchestrated by the suprachiasmatic nucleus (SCN), the master clock, which signals the HPA axis to initiate the cascade of CRH and ACTH release, culminating in the adrenal glands secreting cortisol. Physiologically, this cortisol surge rapidly increases blood glucose availability, modulates immune function, and primes the central nervous system for alertness. A blunted or absent CAR suggests chronic HPA axis dysregulation or exhaustion, correlating with fatigue and poor stress coping mechanisms.

Morning Cortisol Peak

Meaning

The Morning Cortisol Peak, clinically known as the Cortisol Awakening Response (CAR), is the sharp, transient increase in cortisol secretion that occurs approximately 30 to 45 minutes after waking. This physiological surge is a crucial component of the diurnal cortisol rhythm, serving to mobilize energy reserves, enhance cognitive readiness, and prepare the body for the metabolic and psychological demands of the day. A healthy, robust CAR is an indicator of a resilient and well-regulated Hypothalamic-Pituitary-Adrenal (HPA) axis.