Cortisol is a steroid hormone, one of the glucocorticoids, made in the cortex of the adrenal glands and then released into the blood, which transports it all round the body. Almost every cell contains receptors for cortisol and so cortisol can have lots of different actions depending on which sort of cells it is acting upon. These effects include controlling the body’s blood sugar levels and thus regulating metabolism, acting as an anti-inflammatory, influencing memory formation, controlling salt and water balance, influencing blood pressure and helping development of the foetus. In many species cortisol is also responsible for triggering the processes involved in giving birth.
A similar version of this hormone, known as corticosterone, is produced by rodents, birds and reptiles.
Blood levels of cortisol vary dramatically, but generally are high in the morning when we wake up, and then fall throughout the day. This is called a diurnal rhythm. In people that work at night, this pattern is reversed, so the timing of cortisol release is clearly linked to daily activity patterns. In addition, in response to stress, extra cortisol is released to help the body to respond appropriately.
The secretion of cortisol is mainly controlled by three inter-communicating regions of the body, the hypothalamus in the brain, the pituitary gland and the adrenal gland. This is called the hypothalamic–pituitary–adrenal axis. When cortisol levels in the blood are low, a group of cells in a region of the brain called the hypothalamus releases corticotrophin-releasing hormone, which causes the pituitary gland to secrete another hormone, adrenocorticotropic hormone, into the bloodstream. High levels of adrenocorticotropic hormone are detected in the adrenal glands and stimulate the secretion of cortisol, causing blood levels of cortisol to rise. As the cortisol levels rise, they start to block the release of corticotrophin-releasing hormone from the hypothalamus and adrenocorticotropic hormone from the pituitary. As a result the adrenocorticotropic hormone levels start to drop, which then leads to a drop in cortisol levels. This is called a negative feedback loop.
Too much cortisol over a prolonged period of time can lead to a condition called Cushing's syndrome. This can be caused by a wide range of factors, such as a tumour that produces adrenocorticotropic hormone (and therefore increases cortisol secretion), or taking certain types of drugs. The symptoms include:
High cortisol levels over a prolonged time can also cause lack of sex drive and, in women, periods can become irregular, less frequent or stop altogether (amenorrhoea).
In addition, there has been a long-standing association between raised or impaired regulation of cortisol levels and a number of psychiatric conditions such as anxiety and depression. However, the significance of this is not yet clearly understood.
Too little cortisol can be due to a condition called Addison's disease. It has a number of causes, all rare, including damage to the adrenal glands by autoimmune disease. The onset of symptoms is often very gradual. Symptoms may include fatigue, dizziness (especially upon standing), weight loss, muscle weakness, mood changes and the darkening of regions of the skin. Urgent assessment by a specialist hormone doctor called an endocrinologist is required when a diagnosis of Cushing's syndrome or Addison's disease is suspected.
Last reviewed: Jan 2017