What Sleep Deprivation Does to Your Body

If you skip an hour of sleep, you’ll likely wake up feeling more groggy and crankier than usual, but what if you end up missing out on two or three hours? Or what if that single skipped hour or two turns into a regular habit, where you are losing sleep on a nightly basis?

When your body loses valuable sleep and becomes deprived of shut-eye, various things can happen that can affect your mental and physical state in both the short and the long term.

Here’s what experts say happens at each stage of sleep deprivation. It gets scary fast, so read this, then sleep!

What Happens When You Miss Sleep in General

When you lose an hour of sleep, how badly it hurts you depends on where the hour is taken from. “If you go to bed one hour later than normal, you may have been staring at a screen, and that will mean your circadian clock thinks it’s daytime an hour later than usual,” says Ben Smarr, Ph.D., assistant professor in bioengineering & data science at University of California – San Diego, and Sleep Science Advisor for Oura.

When it adjusts to habitual nighttime screen use, you’ll find yourself wanting to stay up more consistently as your clocks align to the new “normal” the habit has created. “That can push you to stay up later and later, which is bad when you have to also align to the rest of the world,” he says. Or even to your own regular morning schedule.

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If you have to wake up earlier than usual, you lose some REM sleep, which tends to happen more toward the end of the night. REM sleep is important for feeling refreshed in the morning as well as for giving you emotional resilience, helping you form memories, and keeping your focus where you need it to be.

As you miss larger and larger amounts of sleep and go farther and farther through the stages of sleep deprivation, the damage increases. Organs need time to replenish and clear waste, as does your brain, and they do it when the rest of your body is resting. The insidious part about sleep deprivation is you don’t often feel it, especially if it’s masked by coffee, Smarr says.

“So your performance, mental resilience and flexibility, and health all suffer, but you might not recognize what a haggard bear you’re becoming,” he says.

You can start to get more sleep though, and fix the damage. “The good news is that the longer you’ve recovered, the more of the damage heals, so while disease risk increases with long-term sleep deprivation, it goes back down once you’re sleeping well again,” he says.

If You Miss One Hour of Sleep

One single hour, one single night, won’t be too bad. “For someone who is well rested, missing an hour of sleep would have relatively minimal consequences,” says Alex Dimitriu, MD, the founder of Menlo Park Psychiatry & Sleep Medicine.

Generally speaking, losing one hour of sleep could leave you feeling groggy, like the sleep wasn’t satisfying. And, no surprise, you might get some daytime sleepiness and yawning, says Azizi Seixas, Ph.D., assistant professor at NYU Langhorne Health.

Even at this stage of sleep deprivation, your immunity might dip a bit. When you sleep, your body produces proteins called cytokines that have immune-boosting effects and serve as fuel for your white blood cells. “Lack of sleep decreases the production of cytokines and makes you more susceptible to bacteria and viruses,” adds Alex Savy, a Sleep Science Coach certified by the Spencer Institute.

If You Miss Two Hours of Sleep

This is the stage of sleep deprivation where you might feel more changes. “When you lose 2 hours of sleep, you may feel significant daytime sleepiness and slight tremors. Your hand-eye coordination is off, and your reflexes might not be as sharp,” says Seixas.

You might also get headaches, says Savy. “Sleep deprivation can elevate your blood pressure because you don’t allow your heart and blood vessels to spend enough time in the ‘rest mode’ at night,” he says.

If You Miss Three Hours of Sleep

On top of all the things that happen when you lose one and two hours of sleep, when you hit the stage of sleep deprivation you get when you cut three hours of sleep out, “you will feel really run down and unable to function,” says Seixas. Extended sleep deprivation can put you at higher risk for a heart attack, he adds. That’s not just due to the risk of elevated cortisol and elevated blood pressure; it’s also because sleep deprivation can make you gain weight, adding stress to all your body’s systems. When people lose significant sleep, “people often crave carbohydrates more. Sleep-deprived lab mice always tend to gain weight,” says Dimitriu.

And sleep-deprived people (even you) aren’t fun to be around, because they’re likely to be grumpy. “Irritability is the result of reduced impulse control, as is bingeing on either food, media, or any other pleasurable activity,” he adds.

Meanwhile, your concentration will be shot. Those who lack quality sleep may take more time to focus and maintain concentration even on simple tasks, says Savy.

If You Miss 4 or More Hours of Sleep

The effects on your health and life at this stage of sleep deprivation start to be super strong at this point. Your brain hasn’t had the opportunity to do its nightly housekeeping, and you’re also extra susceptible to unhealthy eating. When you’re sleep-deprived, a hormone called ghrelin increases, which triggers hunger and cravings. “If you cut half of your recommended sleep per night, you can expect sugar cravings and the urge to eat something deep-fried or baked,” says Savy.

This is also a really good day to call Lyft, Uber, or whatever car service you want. “Drowsiness sets in, as well as lapses of attention, and driving can become dangerous,” says Dimitriu. (In fact, you start getting worse at driving with chronic sleep deprivation of an hour a night.)

Your memory will be less sharp, he says, and your ability to learn new things tanks. And here’s perhaps the scariest fact: at this stage, “a protein, called Tau, which is elevated in people with Alzheimer’s disease, starts to build up,” he says.

Get The Sleep Your Body Needs

Sometimes, the key to sleeping more is prioritizing it. Other times, you need a little help. Check out the bedding, apps, devices and more that earned our sleep awards. Or use these tips to fall asleep faster. And find out why athletes think sleep is the ultimate performance booster. And then get some shuteye yourself.

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