Functions of cortisol in the body

Cortisol belongs to the group of glucocorticoids. It is a vital hormone for humans that is required for a variety of processes in the body.

It is also known as the stress hormone, as it is released in greater quantities under stress in order to fulfil its functions in the body.

The effect strength of cortisol corresponds to the cortisol concentration. The more cortisol is released, the stronger the effects can be.

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1. Stress response

Cortisol is a key hormone in the stress response. When the body is confronted with a stressful situation, more cortisol is released.

Stress includes mental stress and physical stress. Physical stress refers, for example, to infections, trauma, injuries or operations.

As a result of rising cortisol levels, blood pressure rises, the heart beats faster and energy levels are increased. The body is prepared to cope with the stressful situation [1].

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2. Metabolic regulation

Cortisol influences the carbohydrate, fat and protein metabolism. It has a catabolic, i.e. energy-providing, effect. It promotes the conversion of stored carbohydrates into glucose, the breakdown of proteins in the muscles and the conversion of amino acids into glucose in the liver in order to increase blood sugar levels. This provides the body with a quick source of energy, especially in stressful or challenging situations [1-4].

As a consequence, chronic stress in particular can result in more difficult muscle growth or muscle maintenance. Visceral fat is also increasingly stored. Visceral fat is fat that accumulates inside the body around the organs in the abdominal cavity [5].

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3. Immune system

Cortisol has an anti-inflammatory and immunomodulating effect. In acute stress situations, it inhibits the activity of the immune system in order to reduce inflammation and protect the body from excessive immune reactions [6]. For this reason, synthetic glucocorticoids such as cortisone are used as drugs for the treatment of inflammatory diseases and autoimmune disorders.

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4. Regulation of blood pressure

Cortisol influences the blood vessels and helps to maintain normal blood pressure. A low cortisol level can therefore lead to dangerously low blood pressure, while an elevated level can cause blood pressure to rise above normal [6].

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5. Sleep-wake rhythm

Cortisol follows a circadian rhythm [$LINK§], i.e. its level fluctuates throughout the day. Cortisol levels are highest in the morning, which helps to activate the body for the day. Towards evening, the level drops, which prepares the body for sleep. A disruption of this rhythm, for example due to chronic stress, can lead to sleep problems [7,8].

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Excessively high cortisol levels (hypercortisolism)

A chronically elevated cortisol level is known as hypercortisolism. A common trigger for increased cortisol levels is prolonged stress. In some cases, however, it can also be caused by Cushing's syndrome, a condition in which the body produces too much cortisol, either due to a disorder of the adrenal glands or overproduction of ACTH (adrenocorticotropic hormone) in the pituitary gland.

High cortisol levels can cause numerous health problems [9]. These include

• Weight gain
  A persistently elevated cortisol level promotes fat storage, especially in the abdominal area. This is due to increased glucose production and impaired fat metabolism [1-4].
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• Hypertension
  Cortisol leads to a narrowing of the blood vessels and thus increases blood pressure. Long-term high blood pressure can increase the risk of cardiovascular disease.
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• Weakening of the immune system
  Cortisol inhibits the immune system in order to focus all resources on coping with the stressful situation. If the cortisol level is permanently elevated and the immune system is permanently inhibited, this chronic inhibition of the immune response can increase susceptibility to infections.
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• sleep disorders and tiredness
  Permanently high cortisol levels can disrupt the circadian rhythm and lead to insomnia and chronic fatigue.
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• Cognitive Impairments
  Long-term stress and high cortisol levels can affect the brain, especially the hippocampus, which is important for memory and learning.

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Too low cortisol levels (hypocortisolism)

A cortisol level that is too low is also called hypocortisolism. The most common cause of a severely reduced cortisol level is Addison's disease, in which the adrenal glands no longer produce enough cortisol. Hypofunction of the pituitary gland, which controls the production of ACTH, can also lead to low cortisol levels.

Low cortisol levels can be associated with various symptoms [10]. These include

• Tiredness and weakness
  Cortisol plays an important role in energy production. A cortisol deficiency can lead to symptoms such as chronic fatigue, muscle weakness and a general feeling of exhaustion.
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• Low blood pressure
  Cortisol deficiency can lead to low blood pressure. This in turn manifests itself with dizziness and fainting, especially when standing up.
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• Weight loss
  Low cortisol levels can lead to unwanted weight loss and loss of appetite.
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• Salt cravings
  When cortisol is low, the body can no longer retain enough sodium. This can cause a strong craving for salty foods.
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• Depressions
  A lack of cortisol is also associated with mood swings, depression and a loss of emotional stability.