Cortisol: why the lowest number isn’t the healthiest

What does cortisol actually do?

Cortisol is a steroid hormone made by your adrenal glands, which sit on top of your kidneys. They take orders from the pituitary gland, a pea-sized gland just below the brain, which sends out a messenger hormone called ACTH when more cortisol is needed.

NHS hospital patient information describes cortisol as vital for health, and its job list is long. It helps regulate your blood pressure and your immune system, and it works against insulin to keep your blood sugar steady. It’s also a key part of how you respond to stress of any kind. That covers the obvious stuff, like a deadline or a near miss on the M25, but it also covers physical strain such as illness, injury or surgery.

In other words, cortisol is the hormone that keeps the lights on when things get difficult. Most of the time that’s a good thing.

Is high cortisol in the morning normal?

Yes. Cortisol follows a daily rhythm. Levels usually rise in the early hours, peak around the time you wake up and then drift down through the day, reaching their lowest around midnight. That morning surge is part of what gets you up and going. It isn’t a sign that anything is wrong.

That rhythm is also why one cortisol reading on its own tells you very little. NHS laboratory guidance points out that random blood cortisol is of limited use, because the hormone is released in bursts, varies across the day and jumps in response to stress. Several NHS labs ask for blood samples to be taken at about 9am. Oxford University Hospitals goes further and says a random reading taken at another time is uninterpretable.

So if a home kit tells you your cortisol is “high” after a rushed commute and three coffees, that’s your body doing what it’s supposed to do.

Healthy cortisol isn’t low cortisol. It’s cortisol that rises when you need it and falls back when you don’t.

When is cortisol a genuine medical problem?

There are real cortisol disorders. They are uncommon, and they look quite different from ordinary tiredness.

Too little cortisol is called adrenal insufficiency. When the adrenal glands themselves fail, it’s known as Addison’s disease. Symptoms tend to creep up and can include persistent exhaustion, muscle weakness, weight loss, low mood, dizziness when you stand up, and a craving for salty food. It’s investigated with a short Synacthen test. You’re given an injection of a synthetic version of ACTH, and blood samples show whether your adrenal glands respond by making cortisol. The whole test takes about 45 minutes.

Too much cortisol over a long period causes Cushing’s syndrome. The most common cause is steroid medicine, such as long-term prednisolone. Less often it’s a tumour on the pituitary or adrenal gland. NHS guidance on when to test highlights features such as easy bruising, purple stretch marks, a red, rounded face and weakness in the thigh and shoulder muscles. It also flags conditions that are unusual for your age, such as thinning bones, high blood pressure or type 2 diabetes. A random blood test is not used to screen for it. Instead, doctors use an overnight dexamethasone suppression test, which checks whether your body can switch cortisol production off, or repeated 24-hour urine collections, or late-night saliva samples.

Both conditions need specialist tests and an expert to read the results, often an endocrinologist. That’s a long way from a finger-prick kit through the letterbox.

Should I pay for a private cortisol test?

Private blood and saliva cortisol tests are easy to buy online and from high-street clinics. Prices vary widely, and some sell a single cortisol reading while others offer several saliva samples over a day. The trouble is that a one-off number, taken at whatever time suits the courier, runs into exactly the problems NHS labs warn about. A “high” result may just mean you were stressed or it was early. A “low” one may not mean much either.

If you’re worried enough to consider spending money, spend ten minutes with your GP first. Tell them about your symptoms, any steroid medicines you take (including inhalers, creams and joint injections) and how long things have been going on. If cortisol testing is warranted, the NHS will arrange the right test at the right time of day. If it isn’t, your GP can look at the far more common reasons a midlife man feels flat, such as poor sleep, sleep apnoea, low mood, an underactive thyroid, anaemia or too much alcohol.

In England, if you’re aged 40 to 74 and haven’t been diagnosed with certain conditions, you can get a free NHS Health Check every five years. It looks at your blood pressure, cholesterol and diabetes risk. It doesn’t test cortisol, but it covers the things most likely to matter. Scotland, Wales and Northern Ireland don’t run the same scheme, so speak to your GP practice there.

If you have severe symptoms, such as confusion, fainting, bad vomiting or intense pain in your stomach or back, especially if you take steroids, call NHS 111 or, in an emergency, 999.

How do you keep your stress response in good shape?

The useful goal isn’t to suppress cortisol. It’s to give your stress system a chance to settle between demands. For most men the problem isn’t one hormone. It’s a life that never lets the alarm switch off.

Sleep is the big one. Your cortisol rhythm is tied to your body clock, so keeping regular bedtimes and wake-up times, getting daylight in the morning and keeping screens out of the bedroom all help. Persistent snoring with daytime sleepiness is worth raising with your GP.

Exercise briefly raises cortisol, and that’s fine. The hormone falls again afterwards, and regular activity is one of the best-evidenced ways to handle stress, sleep better and protect your heart. You don’t need to punish yourself. Brisk walks, cycling and a couple of strength sessions a week all count.

Go easy on the props. Alcohol may feel like it takes the edge off, but it fragments sleep, and lots of caffeine late in the day does the same. Regular meals help keep your energy steady.

As for supplements, ashwagandha and other so-called adaptogens are widely sold for stress. The research is mostly small, short-term studies, so the evidence that they help is limited. Supplements can also interact with prescribed medicines, so check with a pharmacist before you add one.

Finally, the unglamorous fixes: talking to someone, cutting a commitment, taking the holiday you keep postponing. They cost nothing and nobody will sell them to you, which is probably why you don’t see them advertised.

In short

Cortisol is essential: it keeps your blood pressure, blood sugar and immune system working and helps you cope with stress, and a morning peak is normal. A single random reading, especially from a private kit, tells you little, and lower is not better. Real cortisol disorders such as Addison’s disease and Cushing’s syndrome are uncommon and need specialist NHS tests, so see your GP if you have symptoms rather than chasing a number. For everyday stress, better sleep, regular activity and less alcohol will do more than any supplement.

Sources

• Hull University Teaching Hospitals NHS Trust – Short Synacthen test patient leaflet, including what cortisol does
• University Hospitals Sussex NHS Foundation Trust – Short Synacthen test: purpose and what to expect
• Gloucestershire Hospitals NHS Foundation Trust – Pathology guidance on cortisol testing
• North Bristol NHS Trust – Investigation of Cushing’s syndrome
• Cambridge University Hospitals NHS Foundation Trust – Overnight dexamethasone suppression test patient information
• Oxford University Hospitals NHS Foundation Trust – Clinical biochemistry test catalogue: cortisol