Cortisol is a steroid hormone, known as a glucocorticoid, 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.
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 release 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.
Cortisol levels normally fluctuate throughout the day and night in a circadian rhythm that peaks at about 8 AM and reaches its lowest around 4 AM. While it is vital to health for the adrenals to secrete more cortisol in response to stress, it is also very important that bodily functions and cortisol levels return to normal following a stressful event. Unfortunately, in our current high-stress culture, the stress response is activated so often that the body does not always have a chance to return to normal. This can lead to health problems resulting from too much circulating cortisol or from too little cortisol if the adrenal glands become chronically fatigued.
What happens if one has 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:
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.
What happens if one has too little cortisol?
Chronically lower levels of circulating cortisol have been associated with negative effects such as:
Urgent assessment by a specialist hormone doctor called an endocrinologist
is required when too high or too low levels of cortisol are suspected.