Quick version
Cortisol is a vital hormone that helps the body manage stress, regulate energy and control recovery. In the event of short-term stress, cortisol temporarily rises, while long-term stress can lead to levels that are either too high or too low. By understanding how cortisol works, what symptoms an imbalance can cause and how values should be interpreted, it is possible to get a clearer picture of the body's stress response and when testing may be relevant.
The decisive factor is not whether cortisol is high or low at a single time, but how the system functions over time.
What does the stress hormone cortisol do?
Cortisol is produced in the adrenal glands and is controlled by an advanced signaling system between the brain and the adrenal glands, the so-called HPA axis. The hormone follows a clear circadian rhythm and is at its highest in the morning to help you wake up, raise your blood pressure and mobilize energy. During the day, levels should then gradually decrease as the body moves towards rest and recovery.
In the right amount and at the right time, cortisol is crucial for the body to function normally. It helps you manage stress, regulate blood sugar and blood pressure, reduce inflammation and cope with both infections and physical stress.
Cortisol is therefore not your enemy but rather an essential function in the body's survival process. Problems only arise when the balance is upset.
Why does cortisol rise during stress – and why is it normal?
During acute stress, such as illness, lack of sleep, psychological pressure, intense exercise or anxiety, cortisol rises rapidly. This is exactly how the system is designed to work. The body prioritizes energy, focus and readiness to cope with the situation. In these situations, a blood test can show very high cortisol levels, sometimes up to 800–1000 nmol/L, without it meaning that anything is wrong. In fact, the same person may well have a value around 250–300 nmol/L the very next day, provided that the stress has subsided.
This variation is a sign of a healthy and flexible stress system that can turn on and off as needed.
When high cortisol starts to wear on the body
Problems arise when the stress never really ends. In the event of prolonged sleep deprivation, psychological pressure, anxiety or physical overload, cortisol can be elevated for longer periods or have a disrupted circadian rhythm. Many people then experience a gradual change in the body. Recovery becomes worse, fat accumulates more easily around the abdomen, blood sugar is affected and sleep deteriorates. A common feeling is to always be “on”, without being able to really unwind.
In more unusual cases, severely and long-term elevated cortisol can be due to hormonal diseases, such as Cushing's syndrome. In these cases, very high levels are often seen together with clear physical changes and the condition always requires specialist investigation.
Why can cortisol become low during prolonged stress?
This often causes confusion for patients who have felt stressed over time. Most people associate stress directly with high cortisol, but with prolonged stress, the opposite can actually occur. When the HPA axis has been activated for a long time, the signaling between the brain and the adrenal glands can gradually be attenuated. This does not mean that the adrenal glands are “burned out” – adrenal fatigue is not a medical diagnosis – but that the regulation is working less well.
The body seems to be simply trying to protect itself from constant overactivation. The result can be low or insufficient cortisol levels, especially in the morning. Many people then describe a deep fatigue that cannot be relieved by rest, dizziness when standing up, low stress tolerance and a feeling that the body does not really “get going” despite sleep.
When is low cortisol a sign of illness?
It is important to distinguish between functionally low cortisol in stress-related dysregulation and Addison's disease, which is an uncommon but serious condition. In Addison's disease, the adrenal glands produce too little cortisol and often also aldosterone. This can lead to very low blood pressure, severe fatigue, weight loss, electrolyte disturbances and, in the worst case, life-threatening conditions. Addison's disease always requires medical treatment.
However, the vast majority of people with low or low-normal cortisol do not have Addison's, but a stress-related disorder in the body's regulation.
Why does cortisol vary so much in blood tests?
Cortisol is one of the most sensitive hormones we can measure. The level is affected by several factors at the same time, including time of day, sleep the night before, acute stress, exercise, infection and caffeine. Therefore, a single value rarely tells the whole truth. A high or low test must always be interpreted in its context and sometimes followed up with repeated measurements or additional tests.
It is entirely possible and also completely normal to see large differences between different tests in the same person.
What can you do if your cortisol is out of balance?
Measures depend entirely on why the imbalance has arisen. In the case of a stress-related disorder, it is rarely a matter of pushing the body further, but rather of restoring rhythm, recovery and stability.
Sleep, regular meals, adapted exercise and reduced long-term stress are often more important than quick solutions. If a hormonal disorder is suspected, a medical investigation is always required.
When might it be wise to test your cortisol?
If you recognize yourself in long-term fatigue, stress-related symptoms, difficulties with recovery or suspect that your stress response is not working as it should, a cortisol test can be a first step towards greater understanding. At Testmottagningen, you can test your cortisol level via blood test. It gives an objective picture of how your body is reacting right now – but it is always the interpretation in relation to symptoms, life situation and sampling time that provides the real value.