Cortisol

Cortisol is the principal glucocorticoid hormone in humans. It is produced in the zona fasciculata of the adrenal cortex and released under control of the hypothalamic-pituitary-adrenal, or HPA, axis. Cortisol helps regulate energy metabolism, cardiovascular function, immune activity, and the body's response to physical and psychological challenges .¹

Cortisol secretion follows a daily rhythm as well as responding to stress. Concentrations are typically higher around the start of the active day and lower later in the rest period, with superimposed pulses. Stress, illness, exercise, sleep timing, medications, and many other factors can alter this pattern. Cortisol also feeds back to the hypothalamus and pituitary to help regulate further hormone release .¹

Calling cortisol simply a stress hormone is incomplete. Stress can increase cortisol, but cortisol is continuously involved in normal physiology even without an acute stressor. Its effects also depend on concentration, timing, tissue sensitivity, and duration of exposure. A single blood, saliva, or urine measurement therefore captures only part of a dynamic hormonal system, and different tests are designed to answer different physiological or clinical questions .¹