Does high cortisol really cause belly fat and heart disease?

Short answer

Cortisol gets blamed for belly fat, heart disease, and burnout. The evidence says most of that is wrong. Here is what the data actually shows about cortisol.

Your smartwatch tells you that you're stressed. An influencer tells you that stress means high cortisol, and high cortisol means belly fat, heart disease, and bones turning to dust. That chain of logic sounds airtight. Most of it falls apart when you look at the data.

What cortisol actually does

Cortisol is a steroid hormone secreted by your adrenal glands. Like other steroid hormones, it acts inside the nucleus of the cell, changing how DNA is transcribed. That means it can do a huge number of different things at once, not just one.

Think of cortisol as a hormone designed to save your life in the next ten minutes at the expense of the next ten years. When something bad happens, cortisol pushes sugar into your blood so your muscles and brain can use it, and it ramps down systems you don't need right that second, including your immune system. That immunosuppressive effect is why glucocorticoids like prednisone and hydrocortisone are used as drugs. Hydrocortisone is the exact same molecule your adrenal gland makes.

People confuse cortisol with adrenaline. They come from the same glands and follow similar evolutionary paths, but adrenaline is more cardiovascularly active, flogging your heart. Cortisol is more focused on sugar.

Cortisol also follows a daily rhythm. It is highest in the morning, about five times higher than at night, and lowest in the middle of the night while you sleep. That morning spike is one reason heart attacks cluster in the early hours. Here is the part that gets lost in the wellness conversation. In people who are truly chronically stressed, you often don't see high cortisol. You see a loss of that daily fluctuation. The rhythm flattens out.

Cortisol is a lousy thing to measure

Some lab tests are solved problems. Sodium levels are fast and accurate, and you get the same number twice. Cortisol is not like that.

About 95% of the cortisol in your blood is bound to proteins and inactive. Only the free 5% actually does anything in your cells, but most lab tests measure the total. The correlation between total and free is real but not great. Timing matters enormously because of that daily rhythm. The assays cross-react with other hormones, so false positives are common. You can measure cortisol in blood, saliva, hair, or urine, and they don't all measure the same thing. Drawing blood is itself stressful, which can raise the very number you're trying to capture.

If you don't have symptoms of a cortisol-excess disease, measuring your cortisol is unlikely to give you any useful information.

Where high cortisol genuinely matters

Cushing's syndrome is the real thing. A benign tumor, usually on the adrenal gland, secretes cortisol without regulation. The result is dramatic: a round "moon" face, a fat pad on the upper back called a buffalo hump, deep purple stretch marks on the abdomen, visceral fat, and diabetes. Treatment is removing the tumor.

The influencer move is to take what happens at those sky-high levels and claim that a mildly elevated cortisol in a normal person does a smaller version of the same thing. That is a logical leap, not a proven one.

There are settings where high cortisol tracks with bad outcomes. A 2019 study in PLoS One looked at 139 patients with severe sepsis or septic shock and found those with high cortisol had a tenfold higher risk of death. That is a big effect. It is also observational, so cortisol may just be marking how sick someone already is. Notably, doctors used to give steroids in sepsis on purpose and largely stopped, because the picture is complicated. And most people reading this are not in septic shock.

The heart disease and belly fat claims don't hold up

A 2010 study in the Journal of Clinical Endocrinology and Metabolism followed 861 people over age 65 for six years using 24-hour urinary cortisol. Those in the highest third had five times the risk of cardiovascular death, with no difference in other causes. Sounds alarming. But the things that raise cortisol also independently raise your risk of dying from heart disease: being poor, working nights, chronic stress, other illnesses, less exercise. This is classic confounding. The sample was small, few people died, and the hazard ratio was statistically noisy.

You can't randomize people to different cortisol levels, so researchers reach for Mendelian randomization, which uses genes that predispose to higher or lower cortisol as a stand-in for randomization. Done correctly, comparing siblings who randomly inherited different versions of a gene, it's a clever idea. The published cortisol studies don't do that. They compare across unrelated people in the population, where genes are not randomly distributed and the technique breaks down. For what it's worth, those analyses found genes predisposing to high cortisol raised cardiovascular death risk by only 8%, essentially nothing. That points away from cortisol being causal, even if the method itself is shaky.

Metabolic disease is similar. A 2018 meta-analysis in Psychoneuroendocrinology of 21 studies and nearly 12,000 people found no significant difference in baseline cortisol between people with and without metabolic syndrome. Even confounding couldn't manufacture a link.

Then there's the famous "stubborn belly fat." A 2024 study in Clinical Endocrinology looked at visceral and subcutaneous fat in ordinary people across a range of cortisol levels. In the non-Cushing's range, there was no association between higher cortisol and belly fat. And remember, chronic stress tends to flatten your cortisol rhythm rather than raise it. Patients with PTSD often have lower cortisol than people without trauma.

What actually lowers cortisol, and whether it matters

Some things reliably lower cortisol, and they happen to be good for you anyway. A 2020 meta-analysis in Psychoneuroendocrinology of 58 randomized trials and about 3,500 patients found mindfulness meditation and relaxation techniques each cut cortisol by roughly a third. Yoga, tai chi, cognitive behavioral therapy, and counseling did not show a significant effect. Exercise lowers cortisol. So does sleep, which also keeps that daily rhythm where it should be.

You don't need to detox your cortisol. Ashwagandha does lower it a little, but the endocrine system is already exquisitely tuned to decide when cortisol should be high and when it should be low.

Bottom line

Cortisol too high is bad. Cortisol too low is bad, and it will kill you, as in Addison's disease. It's meant to follow a specific daily pattern. For a healthy person, cortisol is not a useful wellness metric. It's hard to measure, the assays are unreliable, and there's no compelling evidence that a normal-range cortisol level causes heart disease, metabolic syndrome, or belly fat. If you have a moon face, a buffalo hump, or purple abdominal stretch marks, get evaluated. Otherwise, exercise, sleep, and de-stress, but not because of a number on a lab report.

Here's our discussion from the episode:

I covered this in depth on Wellness, Actually, listen below.

Wellness, Actually Podcast

"What's the deal with cortisol?" — Listen to the full episode, including the week's health news and listener Q&A.