What lack of sleep really does to your body

We have, it seems, become a society obsessed with sleep – how much we’re getting, how fractured it is, what constitutes enough… And perhaps it’s not surprising. Since the pandemic began, researchers around the world have been documenting a surge in sleep disorders, fuelled by stress, anxiety and lockdowns, that’s been referred to as “coronasomnia” and just last week yet another study revealed the impact of not getting enough sleep. Researchers at the University of Chicago found that going to bed 75 minutes earlier every night helps you consume 270 fewer calories each day. But it’s not just your weight that suffers when you’re sleep-deprived. There’s barely a bodily function that sleep doesn’t have an impact on, which means a lack of it can have devastating consequences.

“Getting enough good-quality sleep is vital for many aspects of mental and physical health and well-being,” explains sleep psychologist Dr Lindsay Browning, author of Navigating Sleeplessness. “Not getting enough sleep is correlated with an increased risk of depression, anxiety, weight gain, diabetes, heart disease, stroke and a number of other conditions.” In fact, sleep is so important that sleep physiologist Dr Guy Meadows, founder of the Sleep School refers to it as “the ultimate pillar of health and the single most powerful performance-enhancing behaviour known to mankind”. Alongside diet and exercise, sleep has a crucial role to play in making us happier, healthier, fitter and smarter, which is why Dr Browning points out that getting up at 5am to go to the gym is basically sacrificing one healthy behaviour for another – unless you’re going to bed earlier as well.

Why is sleep so important?

“Broadly speaking, sleep is when our brain sorts stuff out,” says Dr Browning. “It gets rid of any unwanted substances, it files and processes new information, it helps produce our immune system and it also helps produce the hormones our body needs.”

These hormones are absolutely crucial to the smooth running of our bodies, as endocrinologist Dr Nicky Keay, clinical lecturer at UCL, chief medical officer of home-blood test company, Forth, and author of the forthcoming book Hormones, Health & Human Potential, explains.

“Hormones control a large number of processes in the body and they are finely tuned to our internal biological clocks, with the levels of hormones released in a timed fashion on a daily, monthly or lifetime basis,” she says. It’s not just that certain hormones are produced when we sleep, it’s that if our sleep is out of sync with what our hormones are doing, we end up with everything out of sync. If you think about how you feel when you’re jet-lagged – all of the body’s processes, from cognitive function to digestion, just don’t seem to be working properly. And not getting enough good-quality sleep is like being in a permanent state of jet lag.

What is 'enough' sleep?

“How much sleep you need varies from individual to individual and is influenced by a variety of factors, including genetics and age,” says Dr Browning. “The more active you are and the more you’re learning, the more sleep you need, so we tend to need less sleep as we get older.” According to Dr Meadows, the vast majority – 97 per cent of the population – need between six and nine hours of sleep a night.

“There is a very small group of people, known as short sleepers, who can be perfectly healthy on just four hours a day,” says Dr Browning. “But this is very rare and you can’t train yourself to be a short sleeper.

“If you fall asleep in under half an hour, don’t wake during the night for more than half an hour, you’re not waking more than about half an hour before your alarm goes off and you feel refreshed when you wake up, you’re probably getting enough sleep.”

Dr Browning also points out that sleep comes in cycles and that it’s quite normal to wake between cycles, even if you’re not aware of it.

“Roughly every 90 to 110 minutes, you’ll go through a full sleep cycle that includes light sleep, deep sleep and dreaming or REM sleep. Almost all of us wake between these cycles, but if you’re not awake long enough to register that, you’ll assume you’ve had unbroken sleep, but it’s quite normal to wake a few times in the night, and not a sign of poor-quality sleep.”

These sleep cycles can also work to your advantage. If you’re struggling to sleep at night, it’s better to work on that, but if shift work or having a young child mean that’s not possible, the aim is to get the number of sleep cycles you need within a 24-hour period, so that might mean two blocks of four hours, or several naps – ideally of around two hours so you’re getting a full sleep cycle.

But if you’re not getting enough sleep, it shows – in the short term – and if it persists over a period of years, in the long term, too (although experts find it difficult to pin down at exactly what point – a year, two years, more – chronic lack of sleep means you can be at increased risk of a range of conditions).

How lack of sleep affects your...

digestion and weight...

We’ve already established that disrupted sleep can throw off your digestion, but as the University of Chicago’s research shows, it can also have an impact on weight loss and weight gain.


sleep weight sleep tired lack of sleep

“Sleep plays a very important role in controlling our appetite hormones,” says Dr Guy Meadows. “It helps to balance out levels of ghrelin, the hormone which controls hunger, and the satiety hormone, leptin. When we are well-rested we can manage our hunger better, and we feel full at the right point.” But without sleep, not only are we more likely to eat more food, but we’re also likely to eat worse food.

“Poor sleep impacts the brain areas responsible for choosing food,” says Dr Meadows. “It means we’re more likely to look for instantaneous energy-release foods, while the sensible bit of the brain that helps with willpower is less likely to stop us making those decisions.” Little wonder then that when you’re exhausted you can’t get enough sweet and fatty foods, and why long-term sleep deprivation is correlated with obesity.

You may know that a lack of sleep boosts levels of the stress hormone, cortisol. Well, cortisol also has an impact on your body composition. Not only is there evidence that high levels of cortisol can cause us to build up abdominal fat, but Dr Kinsella also says that it can break down muscle tissue – and the less muscle you have, the fewer calories you burn, meaning you’re more likely to put on weight.

Then there’s the fact that, as Dr Meadows explains, “even partial sleep deprivation over one night increases insulin resistance, which can in turn increase blood sugar levels”. As a result, a lack of sleep has been associated with diabetes, a blood-sugar disorder.

brain...

“Lack of sleep can have an immediate impact,” says Dr Browning. “If you’re driving and had four hours sleep or less the night before, you’re 11½ times more likely to be in an accident than a driver who slept for seven hours or more.” This is partly down to the fact that sleep deprivation has an instant affect on concentration and attention.

“Even six hours of sleep a night, something many of us routinely get and would not call sleep deprivation, makes the brain less responsive and attentive,” says clinical psychologist, Michaela Thomas.


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Often we might not even register that we’re performing below capacity. “Having an element of fatigue every day, and constantly falling short of your optimal physical and mental performance becomes your new normal,” she says.

Cortisol also plays a part here. “Typically it starts rising in the morning to wake us up and is lowest at night when we’re going to sleep,” says Dr Keay. “But if you’re not sleeping as your body expects, your cortisol levels can stay high.”

According to Dr Martin Kinsella (re-enhance.com), these elevated cortisol levels can have an effect on the brain, causing changes in neurotransmitters that lead to imbalances in serotonin – the happy hormone, which is partly why your mood also suffers.

“People tend to experience an increase in negative feelings and a decrease in positive feelings,” says Michaela Thomas. “Your brain gets excessively emotionally reactive if sleep-deprived, so you can end up irritable and snappy. As a result, lack of sleep is linked to mood disorders such as depression and anxiety.”

And, conversely, symptoms of depression and anxiety can be linked to disordered sleep. But, on the plus side, you can shift this vicious cycle into a virtuous circle by treating one aspect of it. “If you treat the insomnia, the depression will improve, and if you treat the depression, the insomnia will improve,” says Dr Browning.

Sleep disorders have also been associated with an increased risk of dementia, but the evidence on this isn’t clear. “Because dementia comes on slowly, if someone has problems with their sleep – either sleeping too much or too little – it may be an early indicator of dementia, rather than a case of the amount of sleep that they have causing dementia,” says Tim Beanland, head of knowledge management at Alzheimer’s Society.

However, UCL’s professor Gill Livingston, lead author on last year’s Lancet Commission on dementia prevention, thinks that it’s an area worthy of further study.

“We think that having less than six hours sleep in midlife may increase your risk of dementia,” says Prof Livingston. “That’s because during sleep the body clears out one of the proteins related to Alzheimer’s. So we think that aiming for seven or eight hours sleep, but at any rate more than six, is probably a good approach.”

immune system...

You might have heard that when you’re rundown, you’re more likely to pick up every bug going – and it’s true. Sleep is crucial to maintaining the body’s immune system.


sleep weight sleep tired lack of sleep

In fact, in her book Immunity: The Science of Staying Well, Dr Jenna Macciochi says that research has now shown that “a single night of poor sleep leads to a dramatic decrease in natural killer cells – our first-line defence against viruses and potentially cancerous cells. People who sleep six hours a night or fewer are four times more likely to catch a cold when exposed to the virus, compared with those who spend more than seven hours a night asleep.”

And, according to Dr Browning, there’s also evidence that not getting enough sleep the night after a vaccination can result in a weaker immune response, meaning the vaccine isn’t as effective as it might otherwise be.

It’s also why we’re encouraged to rest when we’re ill – and why our clever body makes us feel tired when we’re ill – so that we can sleep more and allow our immune system to respond as efficiently as possible.

And, in the same way that deep sleep helps to consolidate memories, Dr Macciochi says that it also helps our immune system to strengthen immunological memories of previously encountered germs and danger.

She says that there’s also evidence that “if we don’t get enough deep sleep, our capacity to deal with pain is drastically reduced. We are more likely to suffer from aches, headaches or a worsening of any underlying conditions.”

So not only are we more likely to be ill, we’re also more likely to feel like we’re ill.

cardiovascular system...

“Lack of sleep puts you at risk of metabolic syndrome,” says Dr Keay. This is the medical term for a combination of diabetes, high blood pressure and obesity. While we’ve already seen how lack of sleep can be correlated with an increased risk of diabetes and obesity, you’re also more likely to suffer from high blood pressure if you have disrupted sleep. This is partly because blood pressure naturally falls while we’re asleep, but also because raised levels of cortisol can speed up your heart and raise your blood pressure. Add in the fact that chronic sleep deprivation can lead to increased levels of inflammation, which results in a build-up of deposits in the arteries – and thus higher blood pressure – and you can see the problem.


sleep weight sleep tired lack of sleep

According to the NHS website, while “on their own, diabetes, high blood pressure and obesity can damage your blood vessels, having all three together is particularly dangerous [and] puts you at greater risk of getting coronary heart disease, stroke and other conditions that affect the blood vessels”.

In fact, one study found that people who slept less than seven hours per night had an elevated risk of heart failure, while another identified that those sleeping less than six hours per night had a 20 per cent higher chance of a heart attack.

skin...

You might think that getting your “beauty sleep” is an old wives’ tale, but Dr Justine Kluk, a Harley Street consultant dermatologist says that a study that looked at how we perceive people who are sleep-deprived found that “as well as looking more fatigued, observers perceived sleep-deprived participants as being less healthy and less attractive”. And there’s a reason for that. She says: “A 2015 article indicated that chronic poor sleep quality is associated with accelerated skin ageing, diminished skin-barrier function and lower satisfaction with appearance.”


sleep tiredness chronic sleeplessness

There are many factors at play here – it’s partly the increase in general inflammation that contributes to diminished barrier function, but also the high levels of cortisol, which can lead to flare-ups of acne, eczema and psoriasis. There’s also the fact that when we sleep, one of the hormones that is released is human growth hormone. While that’s clearly important in younger people for growth, as we age it’s one of the hormones that is involved in repair and maintenance of the body – everything from muscles to collagen – the protein that gives our skin its youthful bounce.

sex life and fertility...

“There’s a bi-directional relationship between sleep and sex, or sleep and libido,” says neurobiologist Dr Verena Senn, head of sleep research at the mattress company, Emma. “That means the more you sleep, the more sex you’re likely to have, and also the more sex you have, the more sleep you’re likely to get. One study found that with every hour more sleep they get, women were 13 per cent more likely to have sex.” And, of course, the opposite is true as well – but it’s not just a case of being too tired for it.


sleep tiredness

“When we sleep, we produce a lot of hormones linked to stress reduction and relaxation, which means we tend to feel more confident and happy. But we also know that sleep increases levels of testosterone – in both sexes – which has an impact on libido.”

As you might have guessed from the crucial role that sleep has to play in the regulation of all of the body’s hormone systems, there also seems to be some correlation between sleep and fertility.

A review published in the journal of Fertility and Sterility looked at 33 different studies and found that while more research is still needed in this area, sleep did seem to have an impact on both female and male fertility, as well as IVF outcomes.

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