What is the Origin of Diurnal Cortisol Pattern?

The term diurnal comes from the Latin diurnalis, meaning "of the day," emphasizing the day-night cycle that governs this physiological rhythm. The recognition of this specific pattern is fundamental to chronobiology and endocrinology, establishing cortisol as a primary marker of the body's synchronization with the light-dark cycle.

What is the Mechanism of Diurnal Cortisol Pattern?

The pattern is driven by the central circadian pacemaker in the suprachiasmatic nucleus (SCN) of the hypothalamus, which sends signals to the HPA axis. The SCN coordinates the pulsatile release of Corticotropin-Releasing Hormone (CRH) and Adrenocorticotropic Hormone (ACTH), which in turn stimulate the adrenal cortex to synthesize and release cortisol. Disruptions to this mechanism, often due to chronic stress or poor sleep, can flatten or invert the curve, leading to symptoms associated with HPA axis dysregulation and compromised well-being.

Diurnal Cortisol Pattern

Meaning

The Diurnal Cortisol Pattern refers to the predictable, cyclical fluctuation in the secretion and concentration of the stress hormone cortisol over a 24-hour period, which is a key output of the Hypothalamic-Pituitary-Adrenal (HPA) axis. This rhythm is characterized by a sharp rise shortly after waking, known as the Cortisol Awakening Response (CAR), followed by a gradual decline throughout the day, reaching its nadir around midnight. Clinically, assessing this pattern through multiple-point saliva or serum testing provides a nuanced view of adrenal function and stress adaptation, crucial for hormonal balance.