How the level of cortisol changes during the day in people suffering from insomnia.
Somnologist Mikhail Poluektov explains why people with insomnia have increased levels of the “stress hormone”.
What is it
The graph above shows the diurnal changes in the secretion of the hormone cortisol in people with insomnia (red line) and healthy people (blue). Cortisol is a hormone that regulates carbohydrate metabolism in the body and is involved in the development of the stress response. The graph below shows the corresponding ACTH (corticoliberin) levels. It is a hormone that signals the adrenal glands to release cortisol. As we can see, these hormones are characterized by a circadian rhythm of secretion, their curves are practically the same.
Cortisol levels in a healthy person are minimal in the evening, when the nervous system is at its maximum. During the night, cortisol levels gradually begin to rise, with a particularly distinct peak in cortisol secretion in the early morning hours. This is a natural process, which means that the brain prepares to wake up in order to activate all organs in time.
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In people with insomnia, cortisol is not produced correctly. If in a healthy person, the release of cortisol in the evening hours, at 19–20 hours, reaches its minimum, then in a person with insomnia, at this time, the level of cortisol begins to rise, which turns out to be higher than necessary in the evening and at night. There is also more cortisol in the morning than is required.
Why is this interesting for science?
These data confirm that people with insomnia have a constant increased activity of the hypothalamic-pituitary-adrenal axis - the "stress" system that ensures the production of cortisol. Thus, insomnia is not only a problem of night sleep. This is a state of constant excitement of the nervous system, which, in particular, leads to difficulty falling asleep.
The morning peak in cortisol secretion can lead to early morning awakenings with difficulty falling asleep later. Although it is difficult for a person to fall asleep in the evening due to the fact that they have more cortisol than they should, sooner or later the pressure of sleep overpowers the action of the activating systems of the brain, and the person falls asleep. But after a few hours, the sleep pressure decreases, and the person wakes up and again cannot sleep, because in the morning the cortisol level is again too high.
An increase in the incidence of various cardiovascular diseases that occur at the end of night sleep and in the first half of the day is also associated with this peak. For example, episodes of angina pectoris, strokes, heart attacks have a clear peak between 6 am and 12 noon. Elevated cortisol levels contribute to increased blood clotting, and this can lead to vascular thrombosis.
Why know this?
Cortisol is called the stress hormone. But this graph does not directly relate to stress. It shows that people with insomnia have an increased level of excitability of the nervous system. And regardless of whether people with sleep disorders are under stress or not, the activity of the stress system - the hypothalamic-pituitary-adrenal axis - is constantly increased.
But it is obvious that under stress, the excitability of the nervous system increases even more. Thus, stress can be an additional factor in sleep disorders.
