What role does Cortisol play in Müdigkeit?

Cortisol, the primary human glucocorticoid, is often called the 'stress hormone' and plays a central role in circadian rhythm and energy metabolism. Chronically elevated cortisol – due to ongoing stress – can disrupt sleep, impair recovery, and contribute to fatigue. Conversely, adrenal insufficiency (low cortisol) also causes fatigue, lack of drive, and circulatory issues. Evidence for these links comes from endocrinological research and clinical observation, but single-point cortisol measurements (e.g., from saliva or blood) have limited predictive value due to strong diurnal variation. Direct-to-consumer tests that claim to diagnose 'fatigue' from a single cortisol level are not scientifically supported. A proper diagnosis requires multiple measurements (e.g., diurnal profile) and medical interpretation. The provided context lacks specific studies on cortisol and fatigue, so the evidence grade remains general and mechanistic.