The relationship between the hormone cortisol and sleep
Cortisol is the “stress hormone” produced via the hypothalamic-pituitary-adrenal (HPA) axis by the adrenal glands during times of stress. As most cells within the body have cortisol receptors, it is a highly effective chemical messenger, switching a range of functions on and off to adjust to the conditions in which we find ourselves.
By releasing glucose from the liver to increase our energy levels, cortisol enables your body to maintain steady blood sugar supplies to power the rise in heart rate and blood pressure. If you are in the throes of the stress response, extra energy is needed to power the increase in breathing and contract muscles to prepare for action. It sharpens your senses to heighten your alertness and temporarily shuts down the body systems that aren’t needed in the face of crisis, such as digestion and reproduction. All of these functions make cortisol a crucial hormone to protect overall health and well-being.
Like many other physiological processes in the body, cortisol has a circadian rhythm that rises and falls every 24 hours. Studies have shown that blood levels of cortisol reach their lowest around midnight. Levels start to rise at around 02:00 to 03:00 and reach a peak at around 08:30, which helps wake us up in the mornings and gradually decrease throughout the day – however, certain factors interfere with this cycle.
Cortisol and sleep
Naturally, cortisol levels drop when you sleep then rise to wake you, but researchers have found that when the HPA axis is overly active – you are stressed, it can disrupt your sleep cycles. This can lead to fragmented sleep, insomnia and sleep deprivation. This creates a vicious cycle as poor sleep increases stress, further activating the HPA axis and ultimately distorting the body’s cortisol production.
Studies have also shown that insomnia and other forms of sleep deprivation cause your body to secrete more cortisol during the day, perhaps stimulating alertness.
The sleep disorder obstructive sleep apnea causes spikes in cortisol production due to the sudden pauses in breathing which again disrupts the HPA axis, which increases stress levels.