Cortisol

Your adrenal glands, two small glands above your kidneys, make cortisol on orders from your brain, in a rhythm steered by the clock. In the last hours of the night production rises, in the half hour after waking it peaks, and after that it falls over the day to a quarter of the morning value around midnight. That rhythm is the subject itself: cortisol frees sugar and fat, keeps your blood pressure and your blood sugar up, dampens inflammation and readies your body to act. It is the hormone you get up with, and the hormone that shoots up within minutes with an infection, an operation or a fright. That is why a single value cannot say whether you are stressed. Cortisol moves with the hour, with sleep, with a meal, with exertion and with the draw itself, and the labs build that rhythm into their bands: the morning band starts about twice as high as the late-afternoon band. A value that is normal in the morning falls above the band in the afternoon, and the other way round. What a cortisol value can do is show whether the adrenal glands make too little, which gives a deficit at the morning peak, or far too much, which wipes out the rhythm. Your report shows cortisol in nmol/L, with the time alongside. Normal in the morning between 06.00 and 10.00 is about 172 to 497 nmol/L and in the late afternoon between 16.00 and 20.00 80 to 286 nmol/L, where the labs overlap. One of the four reports in µmol/L; converted, the figures are the same.

Most people who have cortisol measured want to know whether their stress has become measurable. That is exactly what this value cannot do. No blood value exists for being burnt out, no lab publishes a limit for it, and a cortisol in the band does not rule out exhaustion while a value outside it does not prove it. Anyone under chronic pressure often has a flatter curve, a lower morning peak and an evening that no longer falls, but you only see that with several measurements over the day, usually in saliva, and even then it is a pattern and not a diagnosis. What the value does serve is the adrenal gland itself. An adrenal gland that makes too little gives tiredness, nausea, weight loss, low blood pressure, a craving for salt and a tanned skin, and then the morning value is low where it should be high. That is Addison's disease, rare but dangerous, and the most common reason it happens is a course of prednisone that has just stopped, after which the adrenal glands need weeks to get going again. An adrenal gland that makes far too much gives a round face, belly fat with thin arms and legs, purple stretch marks, a high blood pressure and a high blood sugar, and then the evening value stays high. That is Cushing's syndrome, and the first test for it is not a morning value but an evening value or a test after a dexamethasone tablet. For anyone who is healthy, cortisol is mainly a value to understand rather than to measure. The rhythm is the lever: light in the morning, a fixed time of getting up, no screens late in the evening, and sleep that lasts long enough keep the peak sharp and the evening low. That is what you feel as energy in the morning and calm in the evening.

A low value belongs to the end of the day: cortisol falls over the day to a quarter of the morning value, and a low late-afternoon value is not a finding but the rhythm itself. A low morning value is what counts. The most common reason is a course of prednisone or another steroid, also an inhaler or an ointment, that stopped shortly before: the adrenal glands are then still quiet and need weeks to get going again. Rare is Addison's disease, in which the adrenal glands themselves fail, or a pituitary that no longer gives the order; a low morning value with symptoms of tiredness, nausea, low blood pressure and a craving for salt should be investigated the same week with a stimulation test. A high value is first a question about the time and the circumstances. Setting a morning value beside the late-afternoon band turns the rhythm into a deviation. A draw after a bad night, a hard training session, an infection, a fright or fear of the needle lifts the value, and that is cortisol doing its job. The pill and a pregnancy lift the total because there is more binding protein, without there being more active cortisol. Prednisolone and prednisone are sometimes mistaken for cortisol by the test and give a falsely high result. A genuinely too high cortisol, Cushing's syndrome, is rare and stands out by the picture around it; the evening value that does not fall is then the clue. Always read cortisol with the time alongside, and beside DHEA-S, which comes from the same adrenal glands but does not move with the clock; together they show what is rhythm and what is store. Sodium, potassium and glucose show whether a low or high value is already working through.