Physical or emotional stress affects the hypothalamic-pituitary-adrenal axis (HPA axis). The HPA axis is a complex network that controls our body’s reaction to stress and regulates a lot of body processes such as the immune response, digestion, energy usage, and mood. This occurs through connections between two glands of the nervous system (hypothalamus and pituitary) and adrenal glands (small organs that reside on top of the kidneys). The glands release various hormones, like corticotrophin-releasing hormone (CRH), cortisol, and others. When these hormones get out of balance, many body systems and functions, like the immune response, can be negatively affected. Cortisol, also called “the stress hormone,” helps to lower inflammation and calm down the immune system. Low levels of cortisol thus may lead to an increase in inflammation and chronic activation of the immune system.
Patients with ME/CFS commonly report physical or emotional stress before they become ill. Some patients with ME/CFS have lower levels of cortisol than healthy people, but their cortisol levels are still within the normal range. Therefore, doctors cannot use cortisol levels to diagnose or treat ME/CFS.