A stress hormone

Cortisol is a steroid hormone that regulates a wide range of vital processes throughout the body, including metabolism and the immune response. It also has a very important role in helping the body respond to stress.
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What is cortisol?
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.

How is cortisol controlled?
Blood levels of cortisol vary throughout the day, but generally are higher 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 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. 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.

What happens if I have too much cortisol?
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:

• rapid weight gain mainly in the face, chest and abdomen contrasted with slender arms and legs
• a flushed and round face
• high blood pressure
• osteoporosis
• skin changes (bruises and purple stretch marks)
• muscle weakness
• mood swings, which show as anxiety, depression or irritability
• increased thirst and frequency of urination.

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.
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.

What happens if I have too little cortisol?
Too little cortisol may be due to a problem in the pituitary gland or the adrenal gland (Addison's disease). The onset of symptoms is often very gradual. Symptoms may include fatigue, dizziness, weight loss, muscle weakness, mood changes and the darkening of regions of the skin. Without treatment, this is a potentially life-threatening condition.
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.