High cortisol: which habits affect it and what levels are concerning, according to doctors

Cortisol is a hormone produced by the adrenal glands, essential for maintaining blood sugar levels, blood pressure, and the body's response to stress. Dr Amalia Ioana Arhire, a consultant endocrinologist and doctor of medicine, explained to Digi24.ro what values are considered normal, what factors can affect them, and when an abnormal result requires medical attention.

Specialists emphasise that a single test with an abnormal value cannot form the basis of a diagnosis — the result must be interpreted alongside the symptoms and medical history of each individual.

The role of cortisol in the body

According to the doctor, cortisol helps maintain blood sugar levels and blood pressure overnight, and plays a role in the body's response to stress, whether physical or psychological. Under normal circumstances, secretion increases between 3:00 and 4:00 in the morning and continues into the early hours of the day, helping the body mobilise for activity. In situations of intense stress — such as a severe infection or surgical procedure — cortisol levels can rise to support blood pressure and blood sugar. The hormone's function is linked to the "fight or flight" response, the mechanism by which the body prepares to react quickly to danger.

Normal values and the importance of collection time

Cortisol follows a circadian rhythm: levels are highest in the morning, around 8:00–9:00, then decline, with another possible variation between 16:00 and 17:00, reaching their lowest point close to midnight, between 00:00 and 01:00.

Serum cortisol measured in the morning should fall between 5 and 25 micrograms per decilitre. For this reason, the time of sample collection is essential — some endocrinological investigations require collection after midnight as well, when the value should be very low.

An elevated result obtained in the morning does not automatically indicate a medical problem, as stress can temporarily alter secretion. For a more accurate assessment, the doctor may also recommend measuring ACTH (adrenocorticotropic hormone, produced by the pituitary gland, which controls cortisol secretion), tested from the same blood sample. Depending on clinical suspicion, the secretion rhythm may also be checked through collections at different times — under normal circumstances, the morning value is two to three times higher than the night-time value.

When elevated levels become a cause for concern

A high level is more concerning when it persistently exceeds the normal range (5–25 micrograms per decilitre for morning serum cortisol). A result above 25 micrograms per decilitre may raise suspicion of hormonal excess, but is not sufficient on its own to confirm a disorder — interpretation also depends on ACTH values, which can vary between laboratories.

If results remain elevated, the doctor may recommend further investigations: urinary free cortisol, measured from urine collected over 24 hours, and salivary cortisol, for which two samples are taken — at night, this should be below 1 nanogram per millilitre.

If investigations confirm a high level, the patient may be referred to an endocrinology service, where a dexamethasone suppression test can be performed to check whether the body is able to reduce its own cortisol production. Monitoring and repeated examinations over several days may be necessary.

The doctor notes that an elevated result does not automatically indicate a tumour of the adrenal glands or pituitary gland. Depression, severe obesity, and excessive alcohol consumption can also influence hormonal secretion, and treating the underlying cause may help normalise values. If the excess is caused by a lesion producing the hormone in an uncontrolled manner, this may be located in the adrenal gland or pituitary gland, and treatment — determined according to the cause — may include surgical removal where indicated.

Symptoms of elevated cortisol

Prolonged excess cortisol can cause persistent fatigue and raised blood pressure, particularly the systolic value. It can also alter the distribution of body fat: weight gain occurs mainly around the abdomen and trunk, whilst the arms and legs may become thinner — a phenomenon associated with loss of muscle mass and thinning of the skin.

Fragile skin may lead to more frequent bruising, and fat may also accumulate in the upper back, visibly altering body shape. From a metabolic standpoint, high values can promote insulin resistance and elevated blood sugar, and over time may lead to raised cholesterol, prediabetes, and high blood pressure.

Cortisol that is too low

A fall in cortisol can occur in certain conditions affecting the adrenal glands, when they no longer produce sufficient hormone. One cause may be an autoimmune disease, in which the immune system attacks the adrenal glands, or trauma and infections affecting these glands.

Low cortisol levels can manifest as marked weakness, loss of appetite, and low blood pressure, and in some cases hypoglycaemia may occur. If adrenal insufficiency is suspected, the doctor may recommend further investigations, sometimes in hospital, including ACTH stimulation tests, which show whether the adrenal glands are capable of producing an adequate amount of hormone.

Factors that promote elevated cortisol

According to the doctor, chronic stress is one of the main factors associated with high values, alongside anxiety, depression, and sleep disorders, which keep the body in a prolonged state of alertness. Persistent pain also plays an important role, repeatedly activating the physiological stress response.

Acute or chronic illnesses, infections, trauma, and periods of intense physical exertion can also alter cortisol values. There are specific medical causes as well, which is why an abnormal result must be interpreted in conjunction with the symptoms and clinical context of each patient.

Daily habits that can influence hormone levels

Insufficient, fragmented, or irregular sleep is among the most significant factors that can influence cortisol secretion. Because the hormone follows a natural circadian rhythm — low levels at night and a rise before waking and during the early morning hours — disruption of this rhythm through poor sleep can affect hormonal balance.