Of all the hormones produced by the body, cortisol is the most misunderstood. It’s essential to any number of biological processes, and yet commonly typecast as “the one to do with stress” – an evolutionary adaptation for different times, wildly unsuited to modern living, something to reduce with meditation, reset with ice baths or regulate with red-light therapy.
Personal trainers will tell you to avoid long runs in case they result in “cortisol belly”, while influencers diagnose “cortisol face” as a sign of too much pressure in the office. To top it all, social media has recently seen the rise of the “cortisol cocktail” – a combination of coconut water, orange juice, salt, and lemon that TikTokers claim can reduce stress and help with weight loss.
But how much of this has any kind of scientific validity – and is worrying about your cortisol levels doing you more harm than good?
The first thing to understand is what cortisol is, and what it actually does: and yes, that does include helping to manage our response to external stressors. In situations that the body perceives as fight-or-flight, it helps the body to produce immediate energy – as well as suppressing non-essential functions such as digestion or repair (we’ll get to whether this is a bad thing or not shortly). “Cortisol plays a vital role in blood-sugar regulation, by prompting the liver to produce glucose and helping ensure a steady supply of fuel to the brain and body,” says Hannah Alderson, a nutritionist, hormone specialist and author of Everything I Know About Hormones. “It also helps modulate inflammation, keeping immune responses in check and preventing them from going into overdrive. It’s key in how we metabolise fat, protein and carbohydrate.” It also regulates blood pressure, can act as a mood buffer, and kicks in to help fight infection if we’re recovering from an acute illness. But one of its most vital roles is also its least talked-about.
“It’s the hormone that gets us out of bed,” says Angela Clow, emeritus professor of psychophysiology at the University of Westminster. “You get this burst of it in the morning, which is called the ‘cortisol awakening response’. That’s not a bad thing or a stress response – it’s the body’s way of waking up and promoting cognitive function. You’ve probably experienced a time when you have an early flight or a busy day ahead, and your body anticipates it and wakes you up without needing an alarm clock. That’s cortisol priming your brain to be more alert and more active, preparing you for the day ahead.”
Research published earlier this year confirmed that cortisol is already increasing from its lowest point about three hours before you wake up – putting to rest any idea that getting up itself is stressful for the body, and suggesting instead that rising cortisol levels are part of what gets us ready for the day. Like every other higher organism on the planet, we’ve evolved to live in an environment that’s dark for (roughly) half of every day, and so our body needs a way to switch from restoration into activity, which seems to be one of cortisol’s key roles.
“A very large proportion of the genes in your body are sensitive to cortisol,” says Stafford Lightman, a professor of medicine at Bristol Medical School and co-author on the recent research. “And so cortisol has a daily rhythm, and that daily rhythm regulates multiple genes in multiple tissues; in your brain, your liver and your immune system.”
As part of this process, cortisol levels gradually decline throughout the day, with periodic bursts approximately every 90 minutes helping to maintain proper bodily function. This certainly isn’t a bad thing, but it does make gauging it difficult: you could take two measurements 30 minutes apart and get two wildly differing numbers. Under laboratory conditions, researchers take cortisol readings from blood or saliva multiple times a day to obtain a general picture of how volunteers’ levels fluctuate and respond to stressors. At-home tests are much less useful: if you’re only testing yourself once or twice a day, the only thing you might notice is that your levels are very high or very low.
So what about the idea that the minor stresses of everyday life are constantly keeping our cortisol levels perilously high? One common characterisation of the way this might work is that our bodies, evolved to deal with sabre-tooth tiger attacks and flash floods, can’t easily distinguish between those sorts of immediate, physical threats and more psychological ones – an argument on the school run, say, or a nasty email from a client. Social stressors, the theory goes, can be insidious: they’re basically ever-present, especially if we’re prone to catastrophise, and if our bodies’ restorative systems switch themselves off every time we encounter them, we’ll never have time for rest and repair.
In baboon troops – which are very social and hierarchical – this effect is visible, with the lower-pecking-order males suffering with worse immunity and shorter lifespans, as their fight-or-flight systems are constantly prioritised over the rest-and-digest ones. But baboon lives tend to be genuinely far more stressful than human ones – if you’re kicked out of the troop or can’t find a mate, you’re facing a genuine, near-immediate threat to your genes’ survival, rather than just feeling a bit put out. There’s speculation, of course, that our bodies can’t make this sort of distinction, and that we still internally respond to having our birthday forgotten at the office like we would to banishment on the savannah. But is that really true?
As it turns out, probably not. To test the effect of short-term bursts of stress, psychologists have developed all sorts of unpleasant laboratory procedures – from cold-water immersion to problem-solving under time pressure, to the Trier Social Stress Test, where volunteers are tasked with delivering a speech and mental arithmetic task in front of an unresponsive panel of evaluators. And the effect isn’t as pronounced as you might have been led to believe.
“Trying to stress a human is really difficult,” says Lightman. “Even plunging your hand into freezing-cold water has very little effect. If you’ve got a really important job interview that is going to govern the rest of your life, then yes, that’s probably going to be stressful. But it’s very subjective – some people, of course, actually like giving presentations in front of a crowd. With things like the Trier test, you might get a reaction the first time, and then you won’t again – just understanding what the test is about is enough to destroy the effect.”
This means you’re unlikely to be suffering spikes in cortisol from the odd snippy Zoom call or altercation at the self-checkout – and, even if your body sees those situations as a threat to your wellbeing, there are other systems that kick in first. “It’s not just cortisol that goes up in stressful situations,” says Dr Thomas Upton, a clinical research fellow who also worked on the recent study. “There are other hormones – like catecholamines, your adrenaline and noradrenaline – that play key roles in the immediate part of the fight-or-flight response. This is what helps you ‘fight the lion’ and get yourself out of the situation, followed up by cortisol release if the stress is strong enough or long enough. What you’re feeling in a very stressful situation like a jump scare is a rush of adrenaline that makes your heart pound and your mouth go dry and all the rest of it.”
Brief, short-term stress is probably not doing you any harm, then. But does this mean heightened cortisol becomes more of an issue when you’re continuously stressed over the long term – for instance, from worrying about a family problem or the mortgage – or even deliberately putting yourself through too many difficult workouts?
“That’s a bit trickier,” says Prof Clow. “If you just have a short burst of perceived stress, you will have a little burst of cortisol. That’s fine: your body will speedily return to normal cortisol secretion. But if you’re chronically stressed, repeatedly getting these bursts, that can affect the regulation of your underlying circadian pattern, which is regulated by your biological clock. So that, instead of having a healthy dynamic pattern of cortisol secretion over each 24 hours, you get ‘flat-lining’, which is not able to regulate other processes adequately.”
Constant stress, then, is probably bad for your cognitive function and health. But cortisol is unlikely to change how you look, unless there are larger problems at play. “If you had Cushing’s syndrome, which is a rare condition where cortisol levels in the body are very high, for example due to a tumour of the adrenal gland, then yes, you might gain extra weight around the stomach, or notice that your face becomes round and puffy,” says Niamh Martin, a professor of endocrinology at Imperial College London. “But that tends to be with very, very high cortisol levels.”
And, while it’s true that something like a long run can elevate cortisol levels over the short term, that doesn’t mean there’s any need to ditch your plans for a new personal best. “Doing, say, a marathon is a massively stressful situation for the body,” says Upton. “You need a cortisol response in that situation, and there’s nothing wrong with it: if you didn’t have that response, the results would probably be terrible. You might actually die.”
The good news, then, is that you can happily ignore the most outlandish advice about keeping cortisol in check with cocktails or cold plunges. Unless you’re suffering from a clear medical issue, you probably also don’t need to worry about how your cortisol’s changing on a daily or hourly basis. Several companies are working on methods for continuously monitoring cortisol levels as you go about your everyday life – but even these could do most people more harm than good. “Something that we’ve seen with glucose monitors is that they create a lot of ‘worried well’ people who put one on, have their breakfast and say, oh hell, my blood sugar’s gone up too much,” says Lightman. “And then they start worrying about doing all sorts of things and make themselves ill. If you’re an Olympic sprinter or something, continuous monitoring might be useful. But, among most people, there’s so much individual variation that the range we call ‘normal’ is huge.”
There’s one more obvious question here, though: if cortisol isn’t the culprit, why does stress seem to go hand in hand with poor health, immune-system disruption and weight gain? “It’s very difficult to unpick,” says Martin. “For instance, many of us have a complex relationship with food – and there are behavioural reasons why we eat besides being hungry – so it’s easy to blame cortisol if we notice that we’re gaining weight, but it might also be that, because we’re stressed, we’re eating in a different way. Similarly, you might be having a tough time at work and that means you don’t have time to exercise, or you’re not sleeping well because you’re stressed and that’s negatively affecting your cortisol levels, rather than the relationship going the other way. Part of the issue is that we still don’t fully understand the chronic stresses that modern life involves and what their impact is on our bodies over a long period of time.”
So what does all this mean for you and your life – stressful or otherwise? “I think the most evidence-backed approach is to treat cortisol as something like a bystander, rather than blaming it for any issues you’re having,” says Martin. “If you’re chronically stressed, that’s something to deal with for health reasons, but it’s not necessarily a question of artificially finding ways to keep your cortisol down – it’s more holistic than that. The most important thing is to look after yourself, rather than reaching for an expensive supplement or a cortisol cocktail or anything like that.”
“There are a few things that seem to help keep cortisol well regulated,” says Clow. “The research suggests, for instance, that the earlier you wake – within reason – promotes a healthy and dynamic cortisol rhythm. So getting plenty of sleep and then getting up relatively early seems to be very good for you. There’s increasing evidence that night-time light exposure inhibits your melatonin secretion, which liberates cortisol and allows it to rise while you sleep.” It’s worth mentioning, though, that getting enough sleep – and on a regular schedule – might be more important.
Physical exercise seems to keep cortisol well regulated but, if you can’t face the gym, that’s not necessarily a bad thing. “Gentle exercise, like walking, stretching or pilates, can regulate cortisol far better than an hour-long Hiit class on an empty stomach,” says Alderson. “Breath work is amazing and you can do it anywhere. Micromoments of joy are a lot simpler to weave in than grand gestures like week-long yoga retreats – and, even if they’re not directly affecting your cortisol, they matter more than people realise. A laugh, a hug, a walk in nature: this stuff really matters.”
Finally, it’s important to remember that, even if modern living does occasionally nudge your hormones outside optimal levels, cortisol is on your side. Your body’s stress response to most things should be good for you. Try to get some exercise every day, sleep on a regular schedule, and eat as sensibly as you can. Don’t worry about the other stuff: you really don’t need the stress.
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