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What Happens Inside Your Body When You Are Sleep-Deprived?

The effects of sleep deprivation can be detrimental to the brain and body.

Sementsova Lesia/Shutterstock
Source: Sementsova Lesia/Shutterstock

I recently returned from a weeklong trip to Hong Kong. During my travels, I used all the strategies that I know work to protect sleep during long-distance journeys: shifting sleep and eating schedules in the direction of destination time, staying hydrated, napping strategically on long flights, and making sure to control the environment (I brought my own sleep kit) — whether plane or hotel — so it’s sleep friendly.

Still, going halfway around the world and back left me somewhat sleep-deprived, and I am pretty good at this. I felt it in everything from my thinking skills, to my appetite, to my mood and my outlook.

It was a potent reminder to me of how truly global the effects of sleep deprivation are to the brain and body, whether it’s the occasional night of too-little sleep or the larger, more chronic sleep debt that so many people face. With that in mind, it feels like a good time for a check-in about the ways that sleep deprivation can interfere with your health, your safety, your relationships, and your performance.

You gain weight.

Poor sleep isn’t the only factor in weight gain, of course — there are several, including your genetics, your diet and exercise habits, your stress, and your health conditions. But the evidence is overwhelming: When sleep goes down, weight goes up.

And it doesn’t take a long time, or a lot of sleep deprivation, to bring the weight on. A fascinating study from researchers at the University of Colorado found that one week of sleeping about 5 hours a night led participants to gain an average of two pounds.

Lacking sleep, you experience multiple changes to your body that can lead to weight gain. Sleep deprivation causes changes to the hormones that regulate hunger and appetite. The hormone leptin suppresses appetite and encourages the body to expend energy. Sleep deprivation reduces leptin. The hormone ghrelin, on the other hand, triggers feelings of hunger — and ghrelin goes up when you’re short on sleep.

Sleep deprivation changes what foods you’re most interested in eating, creating more intense cravings for fat and sugar-laden foods. Low on sleep, your brain can’t make reasoned decisions and use its best judgment about food, and you’re more likely to be impulsive and give in to junk-food desires. (More on the powerful effects of sleep deprivation on the brain soon.)

We also know that even after a moderate amount of sleep deprivation, you’re likely to eat more the next day. And lack of sleep makes you more likely to eat more of your overall calories at night, which can lead to weight gain.

I talked a few weeks ago about a really interesting new study on sleep and sugar consumption, which showed that increasing sleep amounts reduced sugar intake significantly — by about 10 grams. The American Heart Association’s recommended maximum daily intake of added sugar is 36 grams for men and 25 grams for women, which gives you some idea of just how significant a 10-gram reduction really is. That study also showed that boosting sleep amounts started participants on a trend toward lowering their fat and carbohydrate intake.

You have less sex.

You might have seen the recent news that nearly one-third of American couples are interested in a “sleep divorce,” according to a new survey. More than 30 percent of survey-takers said they’d prefer to sleep separately from their partners — and 10 percent said they’d had an earlier relationship end over sleep issues. I understand and support the drive to get a good night’s sleep, even if that means partners sleeping in separate beds. Rather than a “sleep divorce,” I’d prefer to see couples address the fundamental sleep issues that are driving them apart — whether that’s snoring, restlessness, sleeping in a bed that’s too small, or struggling to manage differing sleep schedules.

Attending to the core problems that are leading couples to consider sleeping apart would result in better sleep — and more sex.

We all know being tired can decrease the likelihood that partners will want to have sex — especially at the end of a long day. (Despite the long-held social convention, 10 or 11 p.m. is, biologically speaking, about the worst time to have sex, thanks in large part to low levels of the hormones that drive sexual desire. When are those arousal hormones at their highest? First thing in the morning.)

But the effects of sleep deprivation on sex lives go way beyond the we’re-too-tired-tonight issue.

Sleep deprivation can affect both sexual arousal and sexual function, in both men and women, resulting in less pleasurable, less frequent sex. In men, sleep deprivation lowers testosterone. A recent study found that one week of sleeping just under 5 hours a night sent testosterone levels in healthy young men plummeting 10-15 percent. (There’s also worrisome research accumulating that sleeping too little — or too much — may reduce men’s fertility.) Sleep deprivation is also strongly linked to erectile dysfunction.

In women, sleep deprivation may also lower levels of testosterone, a hormone important to female sex drive. Research shows that sleep deprivation reduces physical arousal and desire in women — and that getting additional sleep boosts next-day arousal. The effects of poor sleep in women haven’t received the degree of scientific attention they deserve. We need more research to understand how sleep deprivation — especially a chronic sleep debt — might contribute to sexual problems in women.

Reading one another’s sexual interest also becomes harder when sleep-deprived. A 2013 study found that men, when sleep-deprived even for a single night, overestimated women’s interest in sex. Scientists attributed this to the effects of sleeplessness on the brain’s frontal lobe, where we assess risk, manage inhibition, and make complex judgment calls.

You look, and feel, older.

I don’t know anyone — man or woman — who wants to look and feel older than they are. Getting plenty of sleep is one way to help prevent that. I call sleep nature’s Botox — and here’s why:

During sleep, particularly during deep, slow-wave sleep, the body produces more human growth hormone, or HGH, and goes to work repairing and refreshing cells throughout the body — including cells of the skin, muscles, and bone. Short on sleep, you risk losing out on this important rejuvenation — and it’s going to show in how you look and feel.

Ever look in the mirror after a few nights of poor sleep and think your skin looks tired? Sleep is critical to the health of your skin — and to its youthful appearance. The boost in HGH is related to increases in the production of collagen, the protein that gives skin its elasticity and firmness, and helps keep wrinkles at bay. Research shows that sleep deprivation interferes with collagen production and can weaken the integrity of the skin.

Healthy, plentiful sleep is important to maintaining muscle mass — and sleep deprivation is linked to both reduced muscle mass and muscle strength in both men and women, particularly with age. Sleep deprivation also can interfere with bone health, reducing bone density and the production of new, strong bone.

Losing strength and mass in muscles and bones can affect everything from your posture to your flexibility to your ability to exercise and be active to how well you heal after injury. To stay looking and feeling youthful, we need our muscles and bones strong and ready to work for us — and they need sleep to do that work.

Your risk for accident and injury goes through the roof.

Whether you’re at home, on the job, on the sports field, or behind the wheel, when sleep-deprived, you’re at much higher risk for accident and injury. I’ve written before about the danger that not getting enough sleep poses to your safety, and research shows how insomnia is a major risk factor for accidental death.

The effects on the brain from sleep deprivation are in many ways similar to the effects of drinking too much alcohol — yet drowsy driving still doesn’t get nearly as much attention as drunk driving. Some of the latest research from AAA shows that drivers who slept even 1 hour less than they typically do are at significantly higher risk for motor-vehicle crashes. And the more sleep deprivation piles on, the higher the crash risk goes. The study found that drivers who slept less than 4 hours the night before had more than 11 times the crash rate as drivers who slept 7 or more hours a night.

The workplace becomes much less safe when you’re sleep-deprived. According to the National Sleep Foundation, highly sleep-deprived workers are 70 percent more likely to be in work-related accidents than well-rested workers.

And a lack of sleep is linked to a higher risk of injury in athletes — including teenage athletes.

Accident risks are often talked about in relation to obstructive sleep apnea — and it’s true that the presence of OSA significantly raises your risk of accident and injury. But not having OSA doesn’t protect you against accidental injury if you’re not getting enough sleep. No matter how your sleep is disrupted or cut short, you’re more vulnerable to accidents.

You don’t heal as quickly from illness and injury

There’s brand-new research which suggests sleep is more important than nutrition to healing. The study is particularly interesting, because the scientists set out to test how a nutritional boost might speed wound healing, even in the presence of sleep deprivation. Instead, they found it was sleep that really accelerated healing — and a lack of sleep slowed it down. This is consistent with other research showing that sleep deprivation slows the healing process.

Sleep has a powerful effect on the immune system, so it’s not just wound healing, but all forms of recovery from illness, injury, and disease, that are affected by sleep. Your risks for coming down with an illness are greater when you’re sleep-deprived, and it will take you longer to recover.

We’ve known for a while of the relationship between sleep and immune function. Both sleep and immune system activity are both regulated by circadian rhythms. And sleep — especially slow-wave sleep — is a time when the body’s immune activity goes into high gear, releasing more of its fighter cells, repairing damaged cells, and pushing back against disease. From the common cold to cancer, we’ve seen scientific evidence supporting sleep’s role in fighting illness.

New research looked at the sleep patterns and immune function in pairs of identical twins, to show that sleep deprivation depresses the immune system. In a study that re-created real-world sleep patterns, scientists found the twins who slept less had less robust immune activity than their longer-sleeping siblings.

If you’re sleep-deprived, you not only weaken your immune system, but you also deprive yourself of the time when body naturally does some of its best work to heal and repair itself.

Remember, when you’re sleep-deprived, you’re not just facing one of these issues: You’re more than likely grappling with all of them. Think about that the next time you’re tempted to shortchange your sleep, because something else seems more important. Next, I’ll talk about how sleep deprivation affects brain function — and changes the way you think and feel.