CortisolStress hormone
A hormone central to the stress response, energy and recovery.
Cortisol is a hormone released by the adrenal glands that mobilises energy, regulates metabolism and coordinates the body's response to stress. It runs on a daily rhythm, rising sharply in the half hour after you wake and tailing off through the evening.
It is not a villain, whatever the internet says. You need it to get out of bed, and it rises normally with hard exercise, cold, illness and any demand worth meeting. A drug that abolished cortisol would not make you calm; it would make you dangerously unwell.
What is worth attention is chronic elevation from persistent stress, short sleep or training you are not recovering from, which shows up as poor sleep, stalled progress and a shorter fuse rather than as a number on a test.
Two popular ideas about it are simply wrong. Adrenal fatigue, the claim that chronic stress exhausts the adrenal glands into underproduction, was examined in a systematic review that found no substantiation for it at all. The tiredness people describe is real; the mechanism offered is not, and chasing it delays finding causes that can be treated. Adrenal insufficiency is a separate, genuine and diagnosable disease.
Cortisol face is the other. Facial puffiness has ordinary causes: sleep, salt, alcohol, fluid shifts, allergy, weight change. Genuine cortisol excess is Cushing's syndrome, a rare condition with a specific clinical picture, diagnosed properly and not fixed by a supplement.
Testing it casually is harder than it looks, because the number depends on the hour, the day, recent stress, illness and hormonal contraception. At home saliva panels are not validated for the interpretations sold alongside them, and a single reading in isolation is close to uninterpretable.
In practice, the levers that work are the boring ones: sleep, total stress load, and not endlessly overreaching in training. Our recovery readiness index tracks the downstream signals rather than the hormone, which is the more honest thing a consumer tool can do.
Sources
Where your own result would sit
Most people reading this page are holding a blood-test report with this marker on it, and the question they arrived with is whether their number is normal. A reference interval says where most results from a healthy population fall; a guideline threshold is where a clinical body draws a line for a decision. Neither is a target, and a result on the wrong side of one is not a diagnosis: the same number can be unremarkable in one person and worth looking into in another, which is why the clinician who ordered the test reads it against your history rather than against a list.
Cortisol has no published interval on this page yet. We hold one, and the dashboard draws it beside a reader’s own result, but it has not been read back against the laboratory’s own page since it was collected. A figure printed beside somebody’s blood result has to have been seen at its source, not remembered, so this one waits.
On your own blood test?
Cortisol is one of the markers FitTools can read from an uploaded blood-test report. You confirm every value before anything is saved, and your results are explained together in one place.