Cortisol is a glucocorticoid hormone synthesized and secreted by the zona fasciculata of the adrenal cortex in response to adrenocorticotropic hormone (ACTH) from the anterior pituitary. It plays a central role in the hypothalamic-pituitary-adrenal (HPA) axis and is the primary stress-response hormone in humans. Cortisol levels exhibit a well-characterized diurnal rhythm, peaking in the early morning and declining to a nadir in the late evening. Cortisol regulates glucose metabolism by promoting gluconeogenesis and glycogenolysis, modulates immune and inflammatory responses, influences protein and lipid catabolism, and maintains vascular tone and fluid balance. Its release is governed by a negative feedback loop in which elevated cortisol suppresses CRH and ACTH secretion from the hypothalamus and pituitary, respectively. Chronic physiological or psychological stress, illness, and circadian disruption can significantly alter this regulatory axis.
Cortisol is a glucocorticoid hormone produced by the adrenal cortex in response to ACTH signaling from the pituitary. It regulates glucose metabolism, immune function, blood pressure, and the inflammatory response. Cortisol follows a strong diurnal rhythm, with peak levels occurring within 30-60 minutes of waking and a nadir around midnight.
Chronically elevated cortisol is associated with Cushing syndrome, characterized by central adiposity, muscle wasting, hyperglycemia, and immune suppression. Low morning cortisol may indicate adrenal insufficiency (Addison disease) or HPA axis suppression from exogenous glucocorticoid use. Single-timepoint cortisol has limitations due to pulsatile secretion and diurnal variation.
Exercise is a potent acute stimulus for cortisol release, with magnitude proportional to intensity and duration. Post-exercise cortisol elevation is a normal part of the stress-recovery cycle. However, persistently elevated cortisol — particularly resting morning cortisol — in the context of declining performance and mood changes is a recognized feature of overtraining syndrome (non-functional overreaching).
Turnaround Time
3 days (up to 12 days)
Fasting Required
No
Method
Immunoassay (ECLIA)
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