What is the Origin of Cortisol Nadir?

The term pairs "cortisol" (the primary stress hormone) with "nadir," an astronomical term of Arabic origin meaning the point directly opposite the zenith, used metaphorically to mean the lowest point. In endocrinology, it precisely denotes the minimum value in the hormone's critical circadian rhythm.

What is the Mechanism of Cortisol Nadir?

The necessary suppression of cortisol production to the nadir is governed by the robust negative feedback loop of the HPA axis and the dominant influence of the circadian rhythm, signaled by the suprachiasmatic nucleus. Melatonin secretion, which peaks during periods of darkness, further supports this suppression, promoting the transition into deep, restorative sleep. Failure to reach this nadir often indicates chronic physiological stress or HPA axis dysregulation, severely interfering with metabolic repair and cellular recovery processes.

Cortisol Nadir

Meaning

The lowest point of the naturally occurring 24-hour cycle of cortisol secretion, which typically occurs around midnight or in the very early hours of deep sleep. This minimum concentration is a critical physiological benchmark, signifying the necessary resting phase and disengagement of the hypothalamic-pituitary-adrenal (HPA) axis. A properly achieved cortisol nadir is absolutely essential for restorative sleep, metabolic repair, and the cyclical regeneration of the adrenal glands.