Cortisol often called stress hormone, and this name reflects its primary function—helping the body cope with stress and unexpected situations. When you face danger or intense anxiety, cortisol triggers the "fight or flight" response: your heart beats faster, your blood pressure rises, your muscles tense, and extra energy in the form of glucose is released into the bloodstream.
Without this mechanism, humans simply would not have been able to survive in the wild for millions of years.
However, cortisol isn't just about stress. Its levels naturally fluctuate throughout the day: peaking in the morning, helping us wake up refreshed and ready for the day, and declining in the evening, allowing us to fall asleep peacefully. It's like an internal alarm clock that synchronizes our energy with sunlight and the activity of the outside world. When this rhythm is disrupted—for example, due to chronic sleep deprivation or working nights—our overall well-being suffers.
It's important to understand that cortisol itself isn't the enemy. Problems arise when it becomes chronically too high or too low. Imagine your car alarm going off every time a fly flies past—soon, both you and those around you will stop paying attention, and the real danger will go unnoticed. It's the same with cortisol: when constantly under stress, its mechanism malfunctions, and the body begins to wear itself out.
What is cortisol from a medical perspective?
Cortisol - This steroid hormone, which is produced in the adrenal cortex, small glands located on top of each kidney. It belongs to the class of glucocorticoids, reflecting its ability to influence glucose metabolism and the adrenal cortex (gluco = glucose, cortex = cortex). Unlike anabolic steroids, which stimulate muscle growth, cortisol acts as a catabolic hormone, meaning it promotes tissue breakdown to mobilize energy.
Its formation is initiated by the hypothalamic-pituitary-adrenal (HPA) axis. The hypothalamus secretes corticotropin-releasing hormone (CRH), which stimulates the pituitary gland to produce adrenocorticotropic hormone (ACTH). ACTH, in turn, stimulates the adrenal glands to synthesize cortisol from cholesterol. When cortisol levels reach sufficient levels, it suppresses the production of upstream hormones, completing a feedback loop.
In the blood, most cortisol is bound to transport proteins—corticosteroid-binding globulin (transcortin) and albumin. Only a small free fraction is active and can affect target cells. The hormone's half-life is approximately 66–110 minutes, after which it is metabolized in the liver and excreted in the urine.
The mechanism of action of cortisol at the cellular level
Upon entering a cell, cortisol binds to special receptors in the cytoplasm. Before encountering the hormone, this receptor is "conserved" by heat shock proteins, such as hsp90. After binding, the hormone-receptor complex travels to the nucleus, where it influences gene function: it can enhance or suppress transcription, that is, the production of messenger RNA, which then serves as instructions for protein synthesis.
This mechanism explains why cortisol's effects don't develop instantly but rather last for a relatively long time. The cell must have time to produce new proteins that will alter its functions. For example, cortisol's anti-inflammatory effect is associated with increased synthesis of proteins such as annexin I, which suppress the activity of enzymes responsible for inflammation.
Approximately 20% of all genes in the human body are under the control of glucocorticoids. This underscores the fundamental role cortisol plays in regulating vital functions. Its influence affects virtually every cell, altering its metabolism, immune response, and ability to heal.
The effect of cortisol on metabolism
The main metabolic function of cortisol is to maintain adequate blood glucose levels, especially during periods of stress or fasting.
It stimulates gluconeogenesis in the liver—the process of creating new glucose from non-carbohydrate sources such as amino acids and glycerol. At the same time, cortisol reduces cellular sensitivity to insulin, reducing glucose uptake by muscle and adipose tissue to conserve it for the brain.
To obtain the building blocks for gluconeogenesis, cortisol triggers protein catabolism, especially in skeletal muscle. It activates the ubiquitin-proteasome system, which breaks down muscle proteins into amino acids. At the same time, the hormone suppresses protein synthesis by blocking the mTOR signaling pathway and reducing the activity of insulin-like growth factor.
In adipose tissue, cortisol acts in two ways: on the one hand, it stimulates lipolysis—the breakdown of fats with the release of fatty acids. On the other hand, when chronically elevated, it promotes fat redistribution, increasing visceral fat deposits and decreasing subcutaneous fat. This is why excess cortisol (Cushing's syndrome) is characterized by thin limbs and a bulky torso with fat deposits on the abdomen, face, and back.
The effect of cortisol on the immune system and other systems
Cortisol is a powerful natural anti-inflammatory and immunosuppressant. It suppresses the activity of virtually all immune system cells, reduces the production of proinflammatory cytokines, and reduces the migration of leukocytes to the site of inflammation. This property is widely used in medicine: synthetic glucocorticoids (prednisolone, dexamethasone) are used to treat allergies, asthma, and autoimmune diseases.
However, chronically elevated cortisol makes the body vulnerable to infections, slows wound healing, and causes thinning of the skin, leading to the formation of striae (stretch marks). It inhibits the function of osteoblasts—the cells that build bone tissue—and increases bone resorption, leading to osteoporosis and an increased risk of fractures.
The nervous system also reacts to cortisol. Excess cortisol often leads to depression, anxiety, and sleep disturbances (difficulty falling asleep, reduced REM sleep). Conversely, a deficiency in cortisol manifests itself as weakness, apathy, and decreased concentration. The hormone also affects the cardiovascular system: it increases vascular sensitivity to adrenaline and norepinephrine and enhances sodium and water reabsorption, which can lead to hypertension.
Clinical significance of cortisol disturbances
Excessively high cortisol levels over a long period of time are called Cushing's syndrome. The causes can vary, including a pituitary tumor (Cushing's disease), an adrenal tumor, or long-term use of hormonal drugs (iatrogenic syndrome). Symptoms include characteristic obesity, muscle weakness, hypertension, diabetes, osteoporosis, and mental disorders. The diagnosis is confirmed by blood, saliva, and 24-hour urine cortisol tests, as well as functional tests.
Cortisol deficiency (Addison's disease) is less common and presents with fatigue, weight loss, low blood pressure, and skin hyperpigmentation (due to elevated ACTH). This condition is dangerous and requires lifelong replacement therapy with synthetic hormones. If any abnormalities are suspected, a consultation with an endocrinologist is necessary, as symptoms can be nonspecific, and only a specialist can accurately interpret test results.
To maintain healthy cortisol levels, it's important to maintain a healthy sleep-wake cycle, avoid chronic stress, regulate physical activity and diet, and limit caffeine in the afternoon. Remember that cortisol isn't an enemy, but a valuable helper, and the goal isn't to suppress it completely, but to maintain its natural rhythm and balance.