What is cortisol?

What is cortisol and how can exercise impact levels of the hormone?

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Does exercise reduce or increase cortisol levels? An endocrinologist explains how the hormone works. 

When it comes to health, there are certain topics that are often spoken about without a thorough understanding. Do you really know how much HIIT is safe to do, for example? And do you really need protein powder to grow muscles? 

One of the buzziest words in health at the moment is cortisol. You’ve probably heard the term ‘spiking your cortisol’ before, and understood that it means something – but without much inclination as to what impact it has on your body.

Well, when it comes to hormones, there’s a lot of misinformation out there, explains Dr Anna Crown, consultant endocrinologist and lecturer at Brighton and Sussex University Hospitals NHS Trust. So we asked her to explain what cortisol really is, and how our exercise, diets and lifestyles can impact it. 

What is cortisol and what causes high cortisol levels?

Cortisol is a hormone that is excreted from our adrenal glands. If you usually associate the idea of ‘spiking cortisol’ with increasing stress, you’re not far off. “Cortisol is responsible for your typical fight or flight response and it enables us to tackle that very acute threat or stress,”  explains Dr Crown. 

The way it does that is by helping you to mobilise blood glucose, moving it from your stores back into the bloodstream. It also helps keep your blood pressure up to deal with a survival-type response.

Cortisol is also responsible for fighting inflammation and sorting our memories, especially those sharp images we form during a period of trauma. “That’s important in terms of survival. If you touch a hot stove as a young child, that is etched in your memory and that protects you because you remember that it was dangerous.”

This all sounds very useful – so why do we worry about our cortisol levels spiking so much? 

Well, the problem is that, most of the time, we aren’t actually fighting for survival when our cortisol spikes. “Think about the Stone Age man. He sees a grizzly bear pop out and tries to attack him, cortisol is a really helpful response,” says Dr Crown. “I think what people worry about now is the fact that we have recurrent psychological or emotional stresses that are not a threat physically but are perhaps a threat to our psychology, we get a similar cortisol response.”

If, for example, you’re in a job that is hugely demanding on your time, where you lack control and a lack of support, you will have “either very frequent cortisol stress responses, or cortisol that doesn’t ever fully settle back to normal again.”

How does exercise impact cortisol?

For all the talk about exercise being a stress reliever, it’s interesting that when you are exercising your cortisol levels will actually go up. “That’s beneficial because during exercise you need to mobilise some of your glucose to keep your blood pressure up. It’s an appropriate response to the stress on your body and your body will use that cortisol to adapt and make changes from the exercise.” 

Woman tired from running
How does exercise impact cortisol?

However, that is only healthy when the cortisol levels come back down again. If you’re really over exercising and under eating, generally, your body would interpret that constant cortisol as a stress, according to Dr Crown. “Your body will try to clamp down on essential functions to help your body manage that,” she says. 

For women, that can present as reproductive systems shutting down. “People who are doing a lot of exercise do need to focus on nutrition, making sure that they are having sufficient calories and a sufficient breadth of calories, not restricting their diets, so that their bodies don’t interpret this as an unhealthy situation,” adds Dr Crown. 

What happens if you have high cortisol levels?

“High cortisol levels over a course of time can actually have damaging effects,” says Dr Crown. That’s because the long term effects of cortisol intensify the short term effects of the hormone: “In the short term it’s helpful to keep your blood pressure up and blood sugar up, it puts you at risk of hypertension and type two diabetes in the long term.”

“Another acute response to cortisol is a sudden hunger. If you are just chronically stressed, this shows as increased appetite.” There’s also a risk of things like depression or problems with memory.

There is a rare condition called Cushing’s syndrome, which is the term for over producing cortisol, but this is “a really, really, really rare condition”, according to Dr Crown, with symptoms including abdominal obesity with very thin muscles and bones on your limbs. 

Lifestyle measures can help you reduce cortisol levels

How can you test your cortisol levels?

Unfortunately, you can’t really. While GPs can send you for a blood test, these almost always show inaccurately high results, says Dr Crown: “You’re going to have a lot of stress in anticipation of a blood test so by definition, if your body system is working well, you’re very likely to have a high cortisol reading. Blood tests will also often be done in the morning when the levels are highest naturally anyway.”

You can visit a private or alternative practitioner for a saliva test, but this is “not a validated way of looking at your cortisol responses.”

How can you reduce cortisol levels?

“This is almost not a medical thing at all, instead it’s more a societal and lifestyle management,” says Dr Crown. That’s because stress management often comes down to following a healthy diet and exercising, but in moderation, and working on your sleep pattern and sleep hygiene.

“There’s increasing evidence that a really important aspect is social support and engagement. In terms of workplaces I think it really is important that people look at ways to support employees and give them more autonomy because that will help reduce stress levels. They should feel rewarded for what they do,” says Dr Crown. 

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Chloe Gray

Chloe Gray is the senior writer for stylist.co.uk's fitness brand Strong Women. When she's not writing or lifting weights, she's most likely found practicing handstands, sipping a gin and tonic or eating peanut butter straight out of the jar (not all at the same time).