Cortisol is a steroid hormone produced by the adrenal glands in response to stress and low blood glucose. It is the primary stress hormone — released as part of the 'fight-or-flight' response — and regulates a wide range of physiological processes.
Cortisol follows a diurnal (daily) rhythm: highest in the morning (30–45 minutes after waking, the 'cortisol awakening response'), declining through the day to its lowest point around midnight. This rhythm prepares the body for activity in the morning and allows rest at night. Disrupted cortisol rhythms are associated with chronic stress, poor sleep, depression and metabolic problems.
Regular moderate exercise, adequate sleep, mindfulness and relaxation practices, social connection, and laughter all reduce cortisol levels. Avoiding chronically high stress states is more effective than acute reduction measures.