Evidence check: Cortisol in the context of stress

Cortisol is a key stress hormone produced by the adrenal cortex and regulated via the hypothalamic-pituitary-adrenal (HPA) axis. In acute stress, cortisol rises to mobilize energy and modulate inflammation. Chronically elevated levels are linked to sleep disturbances, weight gain, and immune suppression. Home tests (saliva, blood, hair) measure cortisol but have major limitations: cortisol follows a strong diurnal rhythm (high in the morning, low at night) and fluctuates due to diet, exercise, and psychological state. A single measurement is therefore rarely meaningful. The evidence for using such tests in stress assessment is primarily observational (human-observational). No randomized controlled trials demonstrate that interventions guided by home cortisol tests outperform standard stress management advice. Additionally, genetic variants (e.g., in NR3C1, FKBP5) can influence cortisol response, which most consumer tests ignore. Conclusion: Cortisol home tests may serve as a rough indicator but are not diagnostic. For suspected chronic stress or adrenal disorders, medical consultation is essential.