Morning cortisol is a marker of adrenal function and stress response. It follows a diurnal rhythm, peaking in the early morning and declining throughout the day. Very low morning cortisol (<5 mcg/dL) may indicate adrenal insufficiency, while elevated levels suggest chronic stress or Cushing's syndrome.
Chronically elevated cortisol directly suppresses the HPT axis, lowering testosterone production. Addressing cortisol through stress management and sleep optimization can improve testosterone levels.