Cortisol

Cortisol is a steroid hormone produced by the adrenal cortex. It helps maintain blood pressure, glucose availability, wakefulness, the stress response and anti-inflammatory regulation. Calling it only the stress hormone is too narrow. Cortisol is needed every day, even when a person feels calm: without it the body cannot adapt normally to load, maintain vascular tone or respond safely to illness.

The key feature of cortisol is its circadian rhythm. It is usually higher in the morning, helps with waking and gradually falls toward evening. A test result without the time of sampling is therefore difficult to interpret. Morning, daytime, evening and nighttime cortisol answer different questions. Sleep, anxiety, infection, pain, caffeine, training, shift work, medications, pregnancy and acute stress before blood draw can all affect the result.

What cortisol regulates

Cortisol helps the liver maintain glucose availability, influences insulin sensitivity, participates in protein and fat metabolism, regulates inflammatory responses and supports blood vessel function. A short-term rise helps the body handle stress. A chronically disturbed rhythm may worsen sleep, appetite, blood pressure, recovery after training and glucose control.

It is not useful to divide cortisol into simply good or bad. Too little cortisol can be dangerous: weakness, low blood pressure, dizziness, weight loss, nausea, salt craving and risk of adrenal crisis need medical evaluation. Too much cortisol is also problematic, especially when it is related to Cushing syndrome, long-term glucocorticoid treatment or severe chronic stress physiology.

How it is tested

Cortisol can be measured in blood, saliva and 24-hour urine. Morning blood cortisol is often used as an initial tool when adrenal insufficiency is suspected, but interpretation depends on timing, symptoms and medications. Late evening or nighttime salivary cortisol can be useful when excess production is suspected, because in a healthy rhythm the level should be low late in the day.

Twenty-four-hour urine measures free cortisol over the day and is used in specific diagnostic situations. Sometimes dynamic tests are needed, such as a dexamethasone suppression test or ACTH stimulation test. These cannot be replaced by home interpretations of symptoms, because fatigue, insomnia and sugar cravings are not specific signs of a cortisol disorder.

What can distort the result

Glucocorticoid medications strongly affect cortisol assessment: tablets, inhalers, creams, injections and nasal preparations can all matter. Estrogens, some anticonvulsants, antidepressants, alcohol, sleep deprivation, acute illness, intense exercise the day before and sudden calorie restriction may also change results. Even stress from the blood draw itself can raise a value.

The result must therefore be read with context. If a person slept three hours, drank a lot of coffee, trained while exhausted and panicked during the blood draw, a borderline elevation is not automatically a diagnosis. If there is marked weakness, low blood pressure, hyponatremia or suspicion of adrenal insufficiency, lifestyle advice about sleep does not replace medical testing.

Keto, LCHF and training

Low-carbohydrate eating does not automatically cause pathological cortisol elevation. But a very abrupt transition, inadequate sodium, severe calorie deficit, poor sleep and overtraining can be perceived by the body as a major load. In that situation, weakness, poor recovery, night waking, food cravings and worse training performance may appear.

On keto, electrolytes, adequate protein, reasonable energy intake and gradual training progression are especially important. If a person restricts carbohydrates, fat, calories and simultaneously increases exercise, the problem may be total stress load rather than keto itself. Sometimes reducing training intensity, restoring sleep, sodium, magnesium and food intake is more useful than looking for a supplement to lower cortisol.

Practical interpretation

Cortisol should be evaluated as a hormone of rhythm, adaptation and safety, not as a universal explanation for every symptom. Testing requires attention to sampling time, material, medications, sleep, illness, training and the purpose of the evaluation. One random value does not show the entire function of the hypothalamus, pituitary and adrenal glands.

When symptoms are mild and clearly related to lifestyle, basic measures are genuinely important: regular sleep, morning light, adequate food, protein, sodium, recovery after training and less evening stimulation. When there are signs of severe excess or deficiency, medical evaluation is needed. A hormonal disorder should not be hidden behind talk about stress, and ordinary stress should not be turned into a diagnosis without evidence.