Cortisol and weight gain: what the evidence supports and when to be tested

Cortisol is a hormone made by the adrenal glands. Social media often describes a stress hormone belly, suggesting everyday stress raises cortisol and drives weight gain around the middle. The NHS sources used for this guide do not describe ordinary life stress as a cause of Cushing's syndrome or of obesity. What they describe is more specific: a medical condition in which there is too much cortisol in the body, most often because of steroid medicine taken for a long time.

That distinction matters. Most people who put on weight around the middle do not have a cortisol disorder, and most will not need hormone testing. A small number do, and for them the cause is treatable, so it is worth knowing which pattern should prompt a GP visit.

The NHS says Cushing's syndrome is caused by having too much cortisol in the body and that you are more likely to get it if you take high doses of steroid medicines for a long time. Sometimes a small, non-cancerous growth in the pituitary gland, near the brain, or in the adrenal glands, near the kidneys, causes too much cortisol to be released. If the problem is in the pituitary gland it is called Cushing's disease; if it is caused elsewhere in the body it is called Cushing's syndrome.

Anyone can get it, but it is much more common in women than in men, and the symptoms often come on gradually. The key point for weight is its distribution: the NHS lists more body fat on the neck, upper back, chest and tummy, with arms and legs that may look thin compared with the rest of the body.

• A red, round face (the redness may be harder to see on brown or black skin).

• Skin that bruises easily and stretch marks on the tummy, hips, breasts and under the arms.

• Muscle weakness, particularly at the top of the arms and legs.

• Low sex drive.

• Mood changes such as irritability, anxiety or depression.

• Irregular periods or periods stopping completely.

• Excessive hair growth (hirsutism).

The NHS lists taking certain medicines, including some steroids, antidepressants and beta blockers, among the things that can make it harder to stay a healthy weight. It also names high-dose long-term steroid medicine as the commonest cause of Cushing's syndrome.

If you are taking steroids and notice these changes, speak to your prescriber. The NHS says that when steroid medicine is the cause, treatment can include gradually reducing how much you take. Stopping steroid tablets suddenly can be dangerous, so the dose should only be changed on medical advice.

The NHS says obesity is often caused by not doing enough physical activity to use up the calories from food and drink, and by eating and drinking more than the body needs, especially foods high in fat and sugar. It adds that you may find it harder to stay a healthy weight if you have an eating disorder or another mental health condition such as depression, have a health condition or disability that makes it difficult to be active, have a learning disability, or have a health condition that causes weight gain, such as polycystic ovary syndrome, an underactive thyroid or Cushing's syndrome.

The NHS list also includes certain medicines, genes that make weight gain more likely, being over 55 and the menopause or perimenopause. A GP will usually consider several of these together. They will ask about medicines, sleep, mood, periods and family history before deciding whether any hormone tests are justified.

The NHS advises seeing a GP if you have symptoms of Cushing's syndrome, particularly if you are taking steroid medicine. In practice that means weight gain together with some of the other features above, such as new easy bruising, stretch marks, muscle weakness, a rounder red face, high blood pressure or new type 2 diabetes. Weight gain on its own, without these features, is usually first approached through diet, activity, medicines review and checks for common causes such as an underactive thyroid.

The NHS notes that Cushing's syndrome is rare in children, and that when a child does get it the main symptoms are obesity and being short for their age.

The NHS says that if a GP thinks you might have Cushing's syndrome they can arrange for the amount of cortisol in a sample of your blood, pee or saliva to be checked. If you have high cortisol you may be referred to a hormone specialist (an endocrinologist) for further tests to check for problems with the pituitary or adrenal glands, which may include blood tests and scans of the brain and kidneys.

Cortisol normally rises and falls through the day and can be pushed up temporarily by illness, poor sleep or some medicines, which is why a single result is rarely taken in isolation and why specialists often use timed or repeated samples. Do not start a home cortisol kit without discussing it with a clinician, because the result is easy to misread.

The NHS says treatment depends on the cause and severity. It can include gradually reducing steroid medicine if that is the cause, medicine to control the amount of cortisol the adrenal glands produce, radiotherapy to treat a non-cancerous growth in the pituitary gland, or surgery to remove a growth in the pituitary or adrenal glands. Surgery to remove the adrenal glands means taking replacement hormones for life. Cortisol is rechecked afterwards and further treatment may be needed if it is still high.

Untreated Cushing's syndrome can cause serious health problems, according to the NHS, including heart attack and stroke, high blood pressure, type 2 diabetes, an increased risk of blood clots, weakened bones (osteoporosis) and kidney stones. This is the reason for taking the pattern of symptoms seriously rather than assuming weight gain alone explains them.

The Pituitary Foundation is named by the NHS as a source of help and support, including helplines and an online support group.

On the NHS the GP arranges the first cortisol checks and refers to an endocrinologist if levels are high. Private endocrinology and direct-to-consumer cortisol tests exist; because results depend heavily on timing and conditions, a clinician needs to interpret them, and a normal result from a home kit does not exclude a problem if the clinical picture fits.