Cortisol

CORTISOL

Glucocorticoids are corticosteroids produced by the outermost layer of the adrenal glands. Their physiological effect is transmitted through numerous glucocorticoid receptors (GR) in the cells. They affect metabolism by promoting the breakdown of fat (lipolysis), boosting the release of amino acids and glucose into the blood and inhibiting the transmission of glucose into muscle and fat cells. Glucocorticoids also affect the immune, bones, cardiovascular and circulatory systems, reproduction and cognitive functions. For example, glucocorticoids boost cardiac muscle contraction and reduce inflammation and the severity of allergic reactions.

The primary glucocorticoid in the human body is cortisol, approximately 15–30 mg of which is secreted daily in the adrenal cortex's middle layer or zone (zona fasciculata). Cortisol production is temporarily spiked by a stress reaction in the body. Afterward, the cortisol levels usually return to normal. Chronic stress may cause permanently elevated cortisol production. Like insulin resistance, this may cause glucocorticoid receptor resistance (GCR). GCR is a predisposing factor for common colds and probably many other inflammatory illnesses.

The adrenal gland secretes cortisol in pulses, following the circadian (daily) and ultradian (hourly) rhythms. For instance, the release of cortisol peaks in the morning, making it easier to wake up and significantly boosting mental energy levels. Cortisol production slowly decreases over the day and is normally at its lowest around midnight. Studies have shown it to be one of the most reliable followers of the circadian rhythm in the body.

The pulsatile nature of cortisol secretion is crucial for normal physiological responses to occur in the body. Animal tests have shown that the lack of pulsatile cortisol secretion impaired hippocampus memory functions and often inhibited acute stress reactions. The disruption of the circadian rhythm is associated with exhaustion, sleep disorders, metabolic disorders and a generally reduced quality of life.