Cortisol: a stress hormone or an essential regulator of the body?

Cortisol is most often portrayed as the "stress hormone" responsible for fatigue, sleep problems, weight gain, and feeling unwell. On social media you can find advice on lowering cortisol, "resetting" the adrenal glands, or spotting an excess based on the shape of the face or the size of the waist.

That picture, however, is heavily oversimplified.

Cortisol is not a toxin, nor a hormone you should have as little of as possible. It is an essential regulator of metabolism, blood pressure, immunity, and the body's response to strain. Both chronic excess and deficiency can be a problem, but genuine disorders of cortisol secretion require proper diagnostic work-up.

What is cortisol?

Cortisol is a steroid hormone produced by the adrenal cortex. Its secretion is controlled by the so-called hypothalamic–pituitary–adrenal axis, or HPA axis for short.

The process runs in several stages:

1. The hypothalamus releases corticotropin-releasing hormone (CRH).
2. CRH stimulates the pituitary gland to release adrenocorticotropic hormone (ACTH).
3. ACTH reaches the adrenal glands and stimulates cortisol production.
4. A rise in cortisol suppresses further CRH and ACTH release through a negative feedback mechanism.

This lets the body adjust cortisol production to the time of day, state of health, physical activity, amount of sleep, and current load.

Among other things, cortisol influences glucose availability, the metabolism of fats and proteins, blood-vessel tone, the workings of the immune system, and the body's ability to respond to stressors.

Cortisol is more than just a stress hormone

The name "stress hormone" is not wrong, but it describes only part of its role. Cortisol does take part in the stress response, yet it is also secreted when we feel no emotional tension at all.

The body needs it around the clock.

The key functions of cortisol

1. It helps keep glucose levels stable

When energy demand rises, cortisol helps make an adequate amount of glucose available to the body. Among other things, it supports glucose production in the liver and limits its use in some tissues.

This allows the brain, heart, and muscles to receive the energy they need during illness, intense exertion, fasting, or other strain.

2. It takes part in regulating blood pressure

Cortisol influences the tone of blood vessels and their response to catecholamines such as adrenaline and noradrenaline. Too little cortisol can lead to low blood pressure, weakness, and dizziness.

3. It regulates the immune response and inflammation

Cortisol limits excessive activation of the immune system. Synthetic glucocorticoids such as prednisone, dexamethasone, and hydrocortisone exploit this mechanism in the treatment of inflammatory, allergic, and autoimmune diseases.

4. It helps respond to threat and strain

In the stress response the body activates, among other things, the sympathetic nervous system and the HPA axis. Cortisol helps redirect energy resources to where they are most needed at a given moment.

5. It influences the sleep–wake rhythm

Cortisol is one of the hormones involved in regulating the circadian rhythm. Its proper variability helps us move from sleep to activity in the morning and prepares the body for rest in the evening.

How does cortisol change during the day?

Cortisol levels are not constant. In a healthy person they follow a circadian rhythm and a pulsatile pattern of secretion.

Levels usually start to rise in the second half of the night, peak in the morning, and then gradually fall over the course of the day. The lowest concentrations typically occur in the late evening and the first part of the night.

After waking, an additional, transient rise may appear, called the cortisol awakening response.

That is why a random cortisol measurement, taken without accounting for the time of collection, sleep quality, medications, and the purpose of the test, may have limited diagnostic value.

Cortisol can rise transiently under the influence of, among other things:

• sleep deprivation,
• pain,
• infection,
• fever,
• surgery,
• intense physical exertion,
• hypoglycaemia,
• emotional tension,
• pregnancy,
• alcohol consumption,
• certain medications.

A single elevated result therefore does not automatically mean an endocrine disease.

Does stress always raise cortisol?

Acute stress usually activates the HPA axis and can increase cortisol secretion. This is a physiological, adaptive response that helps the body cope with a temporary load.

The situation becomes more complicated with chronic stress. Prolonged strain does not necessarily cause consistently high cortisol in the blood. It may affect the circadian rhythm, the reactivity of the HPA axis, and the sensitivity of tissues to glucocorticoids.

Some people show elevated levels, others a flattening of the daily rhythm, and still others a blunted response to subsequent stressors.

When is there too much cortisol?

A pathological, prolonged excess of cortisol is called Cushing's syndrome.

The most common cause of Cushing's syndrome is the use of glucocorticoids, especially in high doses and over a long time. This applies not only to tablets but also to some injections, inhaled preparations, ointments, and other forms of treatment, particularly when they are used in combination.

Endogenous Cushing's syndrome, meaning one that results from the body's own excessive hormone production, is much rarer. It can be caused by, among other things, a pituitary tumour secreting ACTH, an adrenal tumour, or ectopic ACTH secretion by a tumour located outside the pituitary.

Symptoms that may suggest Cushing's syndrome

The more characteristic symptoms include:

• wide, red or purple stretch marks,
• easy bruising,
• thinning of the skin,
• muscle weakness, especially in the thighs and shoulder girdle,
• weight gain with fat accumulating mainly on the trunk,
• rounding of the face,
• high blood pressure,
• disturbances of glucose metabolism,
• osteoporosis or fractures after minor injury,
• menstrual disturbances,
• excessive hair growth in women,
• decreased libido,
• more frequent infections,
• worsening mood and cognitive function.

What matters most is the co-occurrence of several symptoms and their progressive nature. Fatigue, weight gain, acne, or insomnia on their own are not specific enough.

Long-standing Cushing's syndrome increases the risk of hypertension, type 2 diabetes, blood clots, cardiovascular disease, infections, and loss of bone mass.

When is there too little cortisol?

Cortisol deficiency occurs in adrenal insufficiency.

In primary insufficiency the problem lies in the adrenal glands themselves. A classic example is Addison's disease, which most often has an autoimmune basis.

In secondary or tertiary insufficiency the cause is inadequate secretion of ACTH or CRH, linked for example to disease of the pituitary or hypothalamus, or to suppression of the HPA axis by long-term glucocorticoid use.

Possible symptoms of cortisol deficiency

• chronic weakness,
• loss of appetite,
• unintentional weight loss,
• low blood pressure,
• dizziness, especially on standing up,
• nausea, vomiting, or abdominal pain,
• low sodium levels,
• episodes of hypoglycaemia,
• increased craving for salty foods,
• darkening of the skin in primary adrenal insufficiency.

The symptoms are often non-specific, so diagnosis requires clinical assessment and hormonal testing.

Suddenly stopping long-used glucocorticoids can be dangerous. The dose of such medications should be reduced according to a doctor's instructions.

Is "adrenal fatigue" a real thing?

The term "adrenal fatigue" is popular online but is not a recognised medical diagnosis.

According to this concept, chronic stress would gradually "exhaust" the adrenal glands, leading to low cortisol, fatigue, trouble concentrating, cravings for salty foods, and sleep disturbances.

These symptoms are real, but they can have many other causes, for example:

• sleep deprivation,
• anaemia,
• hypothyroidism,
• depression or anxiety disorders,
• nutritional deficiencies,
• sleep apnoea,
• diabetes,
• side effects of medications,
• chronic infections,
• adrenal insufficiency.

The problem, then, is not the reported fatigue itself but attributing it to an unconfirmed "adrenal exhaustion" without proper diagnostic work-up. It is worth checking whether chronic fatigue does not have another, specific cause.

Adrenal insufficiency is a real and potentially serious disease, but it is not diagnosed on the basis of symptoms alone or commercial cortisol profiles performed without a clear indication.

How is cortisol tested?

There is no single universal test that in every situation answers the question of whether cortisol is too high or too low. The choice of test depends on the suspected problem.

When excess cortisol is suspected

Screening tests used to investigate Cushing's syndrome include:

• late-night salivary cortisol,
• free cortisol in a 24-hour urine collection,
• the overnight 1 mg dexamethasone suppression test.

A random blood cortisol measurement is not a recommended screening test for Cushing's syndrome. Nor should the disease be diagnosed on the basis of ACTH alone or adrenal imaging without first confirming abnormal cortisol secretion.

An abnormal result usually requires confirmation with a further test and interpretation by an endocrinologist.

When cortisol deficiency is suspected

The first step may be a morning cortisol measurement, usually together with ACTH. Clearly low results may strongly suggest adrenal insufficiency, whereas intermediate values often require a stimulation test with synthetic ACTH.

Interpretation ranges depend on the laboratory method, so the result should be assessed against the reference ranges of the given laboratory and the clinical picture.

What can distort the test result?

A cortisol measurement can be affected by:

• the time of collection,
• shift work,
• recent waking,
• acute stress,
• intense exertion,
• infection and fever,
• pain,
• pregnancy,
• estrogen-containing hormonal contraception,
• hormone replacement therapy,
• glucocorticoids,
• some anti-epileptic drugs,
• sleep disturbances,
• alcohol,
• an incorrectly performed urine collection.

Estrogens can increase the level of cortisol-binding protein, so total blood cortisol may be higher without an actual excess of free, biologically active hormone.

Before the test, you should tell your doctor about all medications, supplements, ointments, inhalers, and injections you use. You should not stop steroid medications on your own.

Is it worth testing cortisol as a routine screen?

In most healthy people without symptoms suggesting a specific disease, routine cortisol measurement is not necessary.

Testing should follow a justified clinical suspicion. Testing everyone with chronic stress, sleep problems, or weight gain would lead to many false-positive results and unnecessary work-up.

Guidelines recommend investigating for Cushing's syndrome primarily in people:

• with multiple progressive and characteristic symptoms,
• with problems unusual for their age, such as early osteoporosis or hypertension,
• with an incidentally discovered adrenal lesion,
• in children with weight gain combined with slowed growth.

How to support healthy cortisol regulation?

The goal should not be to constantly "lower cortisol". A healthy body needs both the morning rise of this hormone and an adequate response to exertion, infection, or other challenges.

What is worth doing is supporting a healthy circadian rhythm and reducing chronic overload.

Keep a regular sleep schedule

Consistent times for going to sleep and waking up help synchronise the circadian rhythm. Not only the length of sleep matters, but also its quality.

In the evening it is worth limiting bright light, alcohol, and caffeine taken too late. In the morning, exposure to natural light can help. You can read more in the article on how caffeine affects your energy.

Move regularly

Intense training can transiently raise cortisol, and this is a normal physiological response. In the longer term, regular activity improves resilience to stress, sleep, metabolism, and well-being.

A problem can arise when the training load is mismatched to your capacity to recover, especially when intense training is accompanied by low energy availability, insufficient sleep, and strong psychological stress.

Eat enough and regularly

Prolonged calorie restriction, very low energy availability, and frequent episodes of hypoglycaemia represent metabolic stress for the body.

A diet should provide adequate amounts of energy, protein, fats, carbohydrates, vitamins, and minerals.

Reduce chronic overload

The following may help:

• breathing techniques,
• mindfulness,
• psychotherapy,
• contact with loved ones,
• outdoor activity,
• planning rest,
• limiting an excess of obligations,
• treatment of anxiety or depressive disorders.

Not every method works equally well for everyone. The key is finding a strategy you can apply regularly.

Do not treat cortisol with supplements blindly

Products marketed as "cortisol blockers" or supplements that "regenerate the adrenals" do not replace diagnostic work-up. Some may interact with medications, affect blood pressure or glucose, or contain substances not listed on the label.

For a genuine adrenal disease, treatment of the underlying cause, led by a doctor, is essential.

When to see a doctor?

A consultation is advisable when progressive symptoms suggesting excess or deficiency of cortisol appear, especially if they occur together.

Particular attention is needed for:

• wide purple stretch marks and easy bruising,
• marked muscle weakness,
• hard-to-control hypertension,
• a sudden worsening of blood glucose,
• fractures after minor injury,
• unintentional weight loss,
• chronic low blood pressure,
• darkening of the skin,
• disturbances of sodium or potassium,
• long-term glucocorticoid use.

Severe weakness, persistent vomiting, abdominal pain, altered consciousness, very low blood pressure, or fainting may be signs of an adrenal crisis. This is a condition requiring urgent medical attention.

Summary

Cortisol is not the body's enemy. It is an essential hormone that helps regulate metabolism, blood pressure, immunity, the circadian rhythm, and the response to strain.

A short-term rise in cortisol during stress, exertion, or infection is usually normal. The problem appears in the case of a genuine, chronic excess or deficiency of the hormone.

Symptoms attributed to "high cortisol", such as fatigue, trouble sleeping, or weight gain, are non-specific and far more often have causes other than Cushing's syndrome. Often the answer lies in lifestyle or in another cause of chronic fatigue rather than in a single hormone.

Instead of aiming for the lowest possible cortisol level, it is worth supporting its healthy rhythm through sleep, appropriately matched activity, proper nutrition, and recovery. If worrying or progressive symptoms occur, the tests should be chosen by a doctor.

Frequently asked questions

Does high cortisol always mean chronic stress?

No. Cortisol can rise for many reasons, including infection, pain, intense exertion, lack of sleep, pregnancy, or medications. A single elevated result does not allow a diagnosis of either chronic stress or Cushing's syndrome.

Does cortisol cause fat to build up on the belly?

A pathological, prolonged excess of cortisol can promote fat accumulation around the trunk. An increased waist size on its own, however, does not indicate excess cortisol. Far more often it results from energy balance, genetics, age, activity, and sleep quality.

Is a “cortisol face” a reliable sign?

Rounding and redness of the face can occur in Cushing's syndrome, but the disease cannot be diagnosed from the appearance of a face in a photo or video. Facial features are also influenced by genetics, body weight, water retention, medications, alcohol, and many other factors.

What time of day is best to test cortisol?

It depends on the purpose of the test. When deficiency is suspected, cortisol is often measured in the morning. When Cushing's syndrome is suspected, late-night salivary cortisol, a 24-hour urine collection, or a dexamethasone test may be used. The time and type of test should be decided by a doctor.

Can cortisol be lowered through diet?

There is no single diet that treats excess cortisol. Regular, well-balanced meals can support metabolism, sleep, and resilience to stress, but they will not cure Cushing's syndrome. When a disease is confirmed, treating its cause is necessary.

Does coffee raise cortisol?

Caffeine can transiently increase cortisol secretion, especially in people who drink it rarely. This does not mean, however, that moderate coffee consumption causes Cushing's syndrome. What matters are the dose, individual tolerance, timing, and the effect of caffeine on sleep and well-being.

Does intense training raise cortisol?

Yes, especially long or intense exertion can transiently increase its level. This is part of the normal adaptation to exercise. What may be concerning is chronic overload combined with insufficient recovery, low energy intake, menstrual disturbances, declining performance, or recurrent injuries.

Can stress cause cortisol to be too low?

Chronic stress alone is not the same as adrenal insufficiency. A genuine cortisol deficiency can result from disease of the adrenal glands, pituitary, or hypothalamus, as well as from suppression of the HPA axis after long-term glucocorticoid use.

Are home cortisol tests reliable?

A material such as saliva can be used in medical diagnostics, but what matters is how it is collected, the timing, the laboratory method, and proper interpretation. Multi-point commercial profiles marketed as a test for "adrenal fatigue" should not replace diagnostic work-up led by a doctor.

Can you stop taking steroids on your own?

No. Suddenly stopping glucocorticoids after prolonged use can lead to cortisol deficiency and, in extreme cases, to an adrenal crisis. The dose should be reduced according to a plan agreed with a doctor.

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