Here’s What Happens When You Only Get 4 Hours Of Sleep

You might want to stop the late-night scrolling.

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Is 4 hours of sleep bad? Here's how it affects your brain.
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Maybe you’re that person in your friend group who just can’t seem to go to bed early. You know you should — after all, getting plenty of sleep is incredibly beneficial to the human brain — but the allure of scrolling through TikTok into the wee hours of the night (resulting in four hours of sleep or less) wins out most of the time. Meanwhile, your early-rising friends go for a run, make breakfast, and run errands, all before they clock in for work.

But as intense as the morning person versus night owl rivalry may be, it’s not actually the most important predictor of sleep health. Rather than the time you wake up, what’s more important is the amount of good sleep you’re getting each night. If your job requires you to wake up early, yet you also insist on staying up late, that short night of sleep isn’t going to do you any favors.

Human beings require sleep to function, so giving our bodies the right amount of rest is an essential part of everyday life, according to Dr. Tim Woodman, Medical Director at Bupa UK Health Clinics. “It’s no surprise that getting the right amount of sleep for you can help to keep your energy levels up and maintain your attention throughout the day,” Woodman tells Bustle. “A good night’s sleep also helps to strengthen your body’s immune response and allow you time to recover when you’re not feeling well.”

Not only does quality sleep affect your physical wellbeing, but Woodman says it also plays an important role in looking after your mental health, too. No matter how much you convince yourself that four hours of sleep is enough, science isn’t on your side (unfortunately). Here is what the research and experts have to say on the matter of sleep.

How Much Sleep You Should Be Getting

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No one individual is going to require the exact same amount of sleep as another person, and there isn’t really a strictly “normal” amount, according to Woodman. “In general, adults need about seven to nine hours of sleep each night,” he says.

A large-scale 2018 sleep study conducted by researchers at the University of Western Ontario looked at the consequences of sleeping fewer than six hours for eight consecutive nights — the minimum duration of sleep that is necessary to support optimal health in average adults, according to the experts cited in this study. Some 40,000 people participated in the study, which led neuroscientists to conclude that those who slept between seven to eight hours performed better on cognitive tests than those who slept less — and (perhaps surprisingly) those who slept more. Basically, it's all about finding that sweet spot to get a decent amount of shut-eye, and to give your brain the perfect dose of rest that it needs to function to the max.

What Happens When You Don’t Get Enough Sleep

It’s important to find the right balance and get enough sleep, because otherwise you risk impacting your brain and bodily functions. When you don’t sleep properly, your body requires more energy to do day-to-day actions, as it’s working harder to keep you awake, Woodman explains. “It could impair your attention span, concentration, strategic thinking, risk assessment, and reaction times,” he says. “It can make it more difficult to control your appetite and might cause you to gain weight.” The 2018 study found that those who slept for four hours or less performed like they were eight years older during cognitive activities — essentially, getting four hours of sleep is like aging your brain eight years overnight.

Getting too little sleep won’t just affect you the following day, either. Consecutive sleep loss has been associated with “degraded trajectories of daily affective and physical well-being,” according to a 2021 study out of the University of Florida. Three consecutive nights of sleep loss will greatly impact your body and mind, including your mental health. And if you think you can simply repay your sleep debt on weekends and be more productive on weekdays, think again: This study found that even one night of sleep loss can significantly impair your daily functioning.

Although getting four hours of sleep a night doesn't constitute complete sleep deprivation, Woodman explains that it will definitely affect your productivity level and body functions. “For most of us, four hours of sleep per night isn't enough to wake up feeling rested and mentally alert, no matter how well you sleep,” he says. “Not getting enough sleep can lead to health concerns, including impaired memory, lack of alertness, and irritability.”

Researchers have also come to the conclusion that the sweet spot of seven to nine hours per night (the time associated with highly functional cognitive behavior) is typically the same for all adults, regardless of age. However, these crucial hours of rest don't just affect your brain. According to Woodman, “a lack of sleep can increase your risk of developing high blood pressure, diabetes, and coronary heart disease.”

While the odd night here and there of a short amount of sleep likely isn’t bad in the long run, maintaining a regular cycle of around eight hours of sleep is ideal for your well being — even if that means forcing yourself to close TikTok and put down your phone at night.

Studies referenced:

Wild, C. J., Nichols, E. S., Battista, M. E., Stojanoski, B., and Owen, A. M. (2018). Dissociable effects of self-reported daily sleep duration on high-level cognitive abilities, Sleep, Volume 41, Issue 12, December 2018, zsy182,

Lee, S. (2021). Naturally Occurring Consecutive Sleep Loss and Day-to-Day Trajectories of Affective and Physical Well-Being. Annals of Behavioral Medicine. DOI:


Dr. Tim Woodman, Medical Director at Bupa UK Health Clinics

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