Evidence check: Cortisol in the context of fatigue

The provided context does not contain specific evidence on cortisol in relation to fatigue. Cortisol is a stress hormone involved in energy metabolism, but a single measurement (e.g., from saliva or blood) is not clinically interpretable in isolation. Chronically high or low cortisol may indicate dysregulation linked to fatigue – for example, in adrenal insufficiency or Cushing's syndrome. However, such diagnoses require comprehensive testing (e.g., ACTH stimulation, dexamethasone suppression test). Consumer cortisol tests alone cannot explain fatigue. The evidence for cortisol as a standalone biomarker for fatigue is weak; many factors (sleep, diet, stress, thyroid) contribute. Without medical evaluation, self-treatment is not advised.