The real reasons why we sleep

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Perhaps you’ve never really stopped to think about something we do every night of our lives: why do we need sleep?


Simply put, and unsurprisingly, it’s essential for good health—but in more ways than you may think. Sleep is essential to recharge your body and mind so you can function at your best. And generally, most adults need between seven and nine hours of sleep.


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“Sleep is a vital part of our daily lives, yet 70 million Americans suffer from a sleep disorder—and approximately 95 percent of those affected remain undiagnosed and untreated,” says Lauri Leadley, clinical sleep educator and president and owner at Arizona’s Valley Sleep Center.

Sleep has a real impact on your overall health, shares Leadley.


“When we are sleep-deprived, it impacts everything from our physical body to our ability to function to our mental health,” she says. “It only takes one night of lost sleep to impair our judgment equal to that of a drunk driver, according to the National Sleep Foundation.”

Since Leadley says getting enough sleep should be as high on your priority list as exercising and eating right, ahead, we’ll delve into the specific reasons why sleep is so important and answer commonly asked questions about sleep.



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Why do we need sleep?

While there are still a lot of unknowns when it comes to the purpose of sleep, experts do have some theories that help answer the question, “Why do we need sleep scientifically?”


At its core, Leadley explains that sleep is “the only time our body has time to heal,” calling it nature’s method of recharging the body.

Conserve your energy

Sleep is the body’s way of hitting the reset button. As Leadley says, sleep “refreshes your energy to prepare you to meet the challenges of the next day.” The energy savings gained during sleep have been studied and proven through scientific research.

Maintain your brain function

Sleep is an effective way to sharpen thinking, improve memory and retention, and enhance productivity, according to Leadley. In a way, sleep is a way to wipe the brain’s slate clean so one can function better the following day.


“It is possible that one of the essential functions of sleep is to take out the garbage, as it were, erasing and ‘forgetting’ information built up throughout the day that would clutter the synaptic network that defines us,” says one 2017 study. “It may also be that this cleanup function of sleep is a general principle of neuroscience, applicable to every creature with a nervous system.”

Regulate your emotions

Sleep is crucial for regulating emotions, reducing stress, and maintaining mood and good mental health, with studies often linking difficulty sleeping to poor mental well-being.


“The amount of sleep you get and your overall mood are very closely related,” Leadley states. “Everyone knows that one of the surest signs that someone is overtired is that they are irritable and crabby.”


Getting the sleep you need can help stabilize your mood while also decreasing the likelihood of certain mental health conditions, Leadley adds.


“Research indicates that sleep deprivation increases your risk of some mental health conditions like depression,” she says.

Boost your immunity

Scientists are finding more and more that there’s a direct connection between sleep quality and immunity. One 2017 study shows changes in the sleep-wake cycle and immune modulators are linked, which can impact sleep regulation and immune response.

During sleep, there’s a lot going on in your body, says Leadley.


“One of the most important things your body does while you are sleeping is boosting and improving your immune system,” she explains. “If you don’t get enough sleep, it degrades your immune system’s ability to function optimally, making you more susceptible to illnesses of all types from the flu to cancer.”

Protect your heart

Leadley says good sleep can result in better heart health, lowered blood pressure,  and a lower risk of heart attacks and heart disease, something that’s been additionally backed up by scientific research.


“We all know how important it is to promote and protect our cardiovascular health, but not many of us realize the direct connection between cardiovascular health and sleep,” Leadley says. “Not getting enough sleep can contribute to high blood pressure and other cardiovascular system conditions.”


Researchers also believe lack of sleep may increase the risk of dying from a heart attack, she adds.

Prevent diabetes

Research cited by the National Sleep Foundation indicates there’s an association between hormonal changes resulting from sleep loss and an increased risk of developing type 2 diabetes, notes Leadley.

What happens when you sleep?

So, why do we need REM sleep? And why does our body continually cycle through stages of sleep throughout the night? Here, Leadley explains what happens during each stage of sleep:

The beginnings of sleep (pre-sleep)

As your body relaxes and you settle in to fall asleep, your brain activity displays a small, fast wave pattern called beta waves. After several minutes, you enter that twilight-type state of almost asleep as your body continues to relax and your brain switches to alpha waves.


During this timeframe, you may experience hypnogogic hallucinations like feeling as if you’re falling or hearing someone call your name. Myoclonic jerks, the random, sudden, startled movements of a body part, also happen during this pre-sleep stage.

Stage 1: light sleep

Light sleep, the transition from being awake to being asleep, is the first official stage of sleep and the beginning of the sleep cycle. During this stage, your brain shows theta wave patterns on the electroencephalogram (EEG), a recording of the electrical activity in your brain.


Lasting about five to 10 minutes, someone awakened while in this light sleep stage may not even think they’ve slept. Stage 1 is only encountered at the beginning of the first sleep cycle when you fall asleep—and, unlike other stages, isn’t repeated throughout the night.

Stage 2: unconscious sleep

The second stage of sleep lasts for about 20 minutes and is the least active of the sleep cycle stages. Although your brain waves get much more rapid and are punctuated with rhythmic spindles, you appear completely unconscious during this stage.


Your body further relaxes, and your body temperature decreases as your heart rate slows down. This is the first stage where the brain and body begin to have a divergent experience, with the brain becoming more active as the body becomes more passive.

Stage 3: deep sleep

The third stage of sleep is the transition from light sleep to the deepest type of sleep. Your brain activity shows the deep, slow pattern of delta waves during this 20- to 30-minute stage.

Stage 4: deeper sleep

Often called delta sleep because of the delta wave brain activity pattern captured on the EEG, the fourth stage lasts for about 30 minutes, and sleepers in this stage can be very difficult to wake up.


Parasomnias like bedwetting, night terrors, and sleepwalking generally occur during this part of the sleep cycle. This is the last of the N-REM (non-rapid eye movement) sleep stages.

Stage 5: REM sleep

This stage is called REM sleep because of the rapid eye movements that can be observed while you’re in this part of the cycle. When you enter REM sleep, your respiration and brain activity increases. Your brain wave patterns resemble those captured when you’re awake.

This is the stage where the majority of dreaming occurs. Also called paradoxical sleep, during this stage, your brain and body have paradoxical experiences. As your brain activity increases, your body relaxes and all voluntary muscles become paralyzed.


Because REM sleep and wakefulness are so similar from the perspective of your brain, this paralysis, called atonia, is necessary to ensure your body doesn’t act out what your brain is dreaming.


The first REM stage is very short, lasting only a few minutes—but throughout the night, each REM stage will last longer than the previous one, shortening the other stages. By the end of the night, your last REM stage may last as much as 60 minutes.

Your body will continue to cycle throughout the night—but as Leadley points out, contrary to popular belief, people don’t experience sleep stages in a continuous, linear fashion.


“The first cycle generally proceeds from stage 1 to 4 in order, but most people will go back up to stage 3 and 2 before jumping to stage 5 for the first time,” she says.


It usually takes about 90 minutes to reach the first REM stage. “Once the first cycle is complete, you will generally bounce directly back to stage 2 to start the next cycle,” says Leadley. An average night’s sleep repeats a cycle pattern four to five times, she adds.

How much sleep do you need?

You may be wondering, “Why do we need eight hours of sleep?” Well, the answer is a bit more complicated than you may think.

“There are individual differences in sleep needs, but sleep also varies by age,” says Don Townsend, PhD, diplomate, behavioral sleep medicine and fellow, American Academy of Sleep Medicine.


Here are the recommended guidelines for sleep, according to age:

  • Babies: Experts recommend 14 to 17 hours of sleep per day for a baby.
  • Children: Additionally, experts advise school-age children get nine to 11 hours of sleep every day.
  • Teens: According to Townsend, teens often need eight to 10 hours of sleep “but don’t get nearly that much.”
  • Adults: Adults need an average of eight hours of sleep (or seven to nine hours). “There are some controversies about whether older adults under 65 need the same or less sleep or just that their sleep gets redistributed over the typical 24-hour day due to less activity and the other factors that affect older adults, including health issues,” Townsend observes.
  • Seniors: The National Institute on Aging says those over age 65 should aim for seven to nine hours of sleep.

What happens if you don’t get enough sleep?

There are clear side effects that can be felt when you don’t get enough sleep. These signs can include:

  • Anxiety
  • Poor memory
  • Risk of certain diseases
  • Moodiness
  • Irritability
  • Depression
  • Stress
  • Low productivity
  • Low motivation
  • Forgetfulness
  • Inability to concentrate
  • Weight gain
  • Increased appetite
  • Lowered sex drive
  • Lethargy during the day, which can include yawning or needing coffee after coffee

“If you’ve ever gotten out of bed thinking you can’t wait for the day to be over so you can get back in it, chances are you’re not getting enough sleep,” says Leadley.


The bottom line: “Sleep is integral to wellness,” says Leadley. “It impacts every aspect of life—mind, body, and spirit.”

If you can’t sleep—or you struggle to fall asleep, stay asleep, and don’t look forward to those restful hours—consider signing up for a sleep study to see if there’s a deeper issue, suggests Leadley.


“A diagnosis and treatment plan can vastly improve your sleep health—and whole life,” she says.


What are three reasons why sleep is important?

Sleep is crucial for your overall wellness. Some of the top ways your life can be impacted by lack of sleep include lowered energy, poor mental health, and risk for developing certain diseases.

What happens if you don’t sleep?

Your mind and body will be quickly, and directly, affected. You’ll experience heightened stress, brain fog, and increased appetite, among several side effects.


Beyond physical sleep, there are other types of rest that can help you recharge. Here’s a rundown of the different types of rest and why they’re important.

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Can alcohol actually help you sleep?



I’ve never been a huge drinker, but I’ve definitely imbibed more than usual over the last year and a half. With all the added stress from the pandemic, I’ve found myself reaching for a large glass—or two, let’s be real—of wine almost every night.


Not only does drinking alcohol leave me with a serious case of acid reflux, though, but it also makes getting a good night’s sleep pretty difficult. That’s not surprising, given studies show alcohol negatively impacts sleep.


“While some people notice that an alcoholic drink or two causes drowsiness and aids them in falling asleep, there is evidence to suggest that alcohol, particularly in high doses, can interrupt and negatively affect the quality of one’s sleep,” says Emma M. Laing, PhD, RDN, clinical associate professor and director of the didactic program in dietetics at the University of Georgia.


To get my sleep (and health) back on track, I’ve decided to temporarily quit drinking and do a dry month challenge. Here, learn more about how alcohol affects sleep and the many benefits you can expect from a dry month.


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In general, alcohol quickens how fast you’ll fall asleep — and it also makes it harder for noise and commotion to wake you up.


Research shows alcohol increases the amount of time spent in slow-wave sleep, the deepest stage of sleep, although recent data suggests this only happens in people who are already deficient in deep sleep. (This could be the case if you have a sleep disorder, like sleep apnea.)


These effects only occur in the first part of sleep, usually within the first four hours of the night as your body metabolizes the alcohol. Once your body has broken down all of the booze, you’ll start to experience worse sleep. Now you’re awakened and can be aroused from sleep more easily.


Why is that? According to studies on alcohol and sleep, you tend to spend more time in the lighter stages of sleep and REM sleep (the period when you dream) during the later part of the night, after you’ve thrown back a few cocktails.


In general, most people can metabolize one drink every one to two hours. But when it comes to how alcohol will affect your individual body and sleep, a lot of factors come into play. These include:

  • What you drink: Some types of booze have a higher alcohol content than others and will therefore hit you harder. A standard serving of beer (12 ounces) usually has around 5% alcohol; a standard serving of wine (5 ounces) usually has around 12% alcohol; and a standard serving of distilled 80-proof liquor (1.5 ounces) usually has around 40% alcohol.
  • How much you drink: The more alcohol you drink, the higher your blood alcohol concentration (BAC) will be.
  • How quickly you drink: The faster you down drinks, the higher your BAC will be.
  • Your gender: Alcohol affects men and women differently. Women tend to weigh less than men and ultimately tend to get intoxicated more quickly. Women also have less dehydrogenase, the enzyme that breaks down alcohol in the stomach. This can lead to higher BACs for women even if they drink the same amount of alcohol as men.
  • Your body size: People with smaller body sizes will feel the effects of alcohol faster.
  • What you eat: Food also plays a role in how alcohol will affect you. Having something in your stomach, whether it’s carbs, fat or protein, will help slow down the absorption of alcohol into the bloodstream. The larger the meal and the closer you time it to your drinking, the lower your peak BAC is likely to be.

That said, research shows as little as one drink could worsen your sleep, regardless of your gender or your weight. A 2018 study found that one drink reduces the restorative quality of sleep by 9.3%. Moderate alcohol consumption (three drinks), meanwhile, was shown to lower sleep quality by 24%. High alcohol consumption (seven drinks) was shown to decrease sleep quality by as much as 39.2%.


Results were similar for women and men, as well as for people of smaller and larger body sizes and people who were physically active versus those who were more sedentary.


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Research shows alcohol can increase the amount of deep sleep people with insomnia get. But this increase in deep sleep is only temporary. After about six nights, people with insomnia will start to develop a tolerance to alcohol and need to drink more to get the same effect, according to one study.


While the research isn’t conclusive, it does suggest using alcohol as a sleep aid for insomnia could increase the risk of alcohol abuse.


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There’s a link between alcohol consumption and sleep apnea. Alcohol depresses the central nervous system, slowing down the part of the brain that controls breathing, along with the firing of the muscles that keep your airway open. When you have sleep apnea, this part of the airway gets repeatedly blocked during sleep. This causes brief arousals throughout the night.

Moderate to heavy drinking can lead to episodes of sleep apnea, even if you don’t have the condition. And for people who do have sleep apnea, studies show drinking can exacerbate this problem.


Yes, alcohol can disrupt sleep. While it has sedative effects that can cause feelings of sleepiness, studies show alcohol, particularly when consumed in excess, can reduce sleep quality and sleep duration.


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Drinking alcohol isn’t going to do your sleep any favors. But if you’re smart about when, what and how much you imbibe, a glass (or two) of Pinot noir won’t necessarily ruin your night, either. Here are a few tips to keep in mind:

  • Stop drinking a few hours before bed. Exactly how long you should leave between your last drink and hitting the pillow depends on how much you drink and how quickly your body metabolizes alcohol. Most of us metabolize about one drink every one to two hours.
  • Don’t overdo it. The more drinks you consume, the longer it takes your body to metabolize the alcohol. Regardless of whether your body metabolizes alcohol quickly or slowly, the less alcohol in your system, the less potential for your sleep to get disrupted.
  • Watch out for heavy pours. Stick to standard-size drinks, not doubles, extra-large wine glasses or mixed drinks with multiple shots of different liquors. Bonus: You’ll certainly save money the next time you hit the bar.


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Now you know all the ways alcohol can wreak havoc on your sleep. So naturally, you might be wondering whether taking a break from booze could improve your shut-eye.


Here’s what you need to know about Dry January, the benefits of doing a dry month, and how to stick with it to experience the best results.


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Dry January involves taking a month-long break from alcohol. Because it begins on January 1, some people participate in Dry January to kick-start a New Year’s resolution to cut back on alcohol. Other people use it as a way to reset after lots of holiday drinking.


The first Dry January took place in 2013. The campaign originated with Alcohol Concern, a U.K. organization, as a way to encourage mindfulness around alcohol consumption.


That first year, 4,000 Brits took the challenge, and it’s since expanded worldwide. Close to 25% of Americans reported interest in participating in Dry January in 2019.


Other popular months to stop drinking include September and October, which you’ll often see referred to as Sober September and Sober October. But really, you can do a dry challenge any month of the year.


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Even taking a short hiatus from drinking alcohol can result in better quality sleep. According to 2015 research out of the University of Sussex, 62% of Dry January participants reported better sleep.


“Appreciating the various ways in which alcohol can disrupt sleep, it makes sense that taking a break from drinking can result in more restful nights,” says Laing.


She does note, however, that heavy drinkers who decide to stop drinking abruptly may experience withdrawal symptoms before they start to see the sleep benefits. “Multiple factors, including how much and how often you drink, can contribute to the severity of these withdrawal symptoms,” she says.


Hilary Sheinbaum, journalist and author of The Dry Challenge: How to Lose the Booze for Dry January, Sober October, and Any Other Alcohol-Free Month, first took the Dry January challenge in 2017 and noticed improvements in her sleep.


“When I gave up alcohol for one month, one of the most surprising epiphanies was my quality of sleep,” she says. Before taking the challenge, Sheinbaum says she used to sleep an average of five hours a night, often waking up in the middle of the night.


“I truly thought that was due to my crazy-busy New York City life, my around-the-clock job and my anxiety as a whole,” she says. “Nope! Not long into my first Dry January, I realized that even though my work and lifestyle were as busy as ever, I was sleeping seven to eight hours each night, which was a personal record.”


The only change Sheinbaum had made in her life? Giving up alcohol.


Laing says additional health benefits of cutting out alcohol, even for a short period, include an improved immune system and liver function, as well as a heightened ability to curb mindless snacking.


Per the University of Sussex research, 62% of Dry January participants reported more energy, while 82% felt a sense of achievement. Additionally, 49% of participants said they lost weight.


One of the more surprising benefits for Sheinbaum, meanwhile, had to do with her skin.


“My skin looked infinitely clearer and more glowy, even in the dead, dull, month of January,” she says. “As it turns out, alcohol dehydrates your body, including your skin.”


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A month without booze might sound daunting, but there are some things you can do to ensure the process goes smoothly, no matter if you plan it for January or any other month:

  • Be clear about your intentions. Make a list of the top reasons you’re giving up alcohol to remind yourself why you’re taking this break in the first place, suggests Laing. “Keep your list in a prominent place and refer to it when the urge to drink strikes,” she says. “If possible, talk about your intentions with your friends, family, and your healthcare provider, so they understand and are able to offer support when needed.”
  • Enlist a friend to do it with you. “For first-timers, I suggest recruiting a friend or friends to partake in the challenge with you,” says Sheinbaum. Her first Dry January stemmed from a spontaneous bet she made with a friend on New Year’s Eve in 2016. “The first year I did the dry challenge, and made a Dry January bet, it felt like a group effort,” she says. “It was so helpful to have a friend to keep me accountable—and also share tips and tricks along the way.”
  • Replace drinking with another activity. These last few months, I’d always reach for a glass of wine at the end of a stressful day. But there are healthier ways to relieve anxiety, and Dry January is the perfect time to incorporate some of these activities into your routine. Try taking a relaxing bath, going for a walk around the block with your pet or cooking a new recipe, says Laing.
  • Keep alcohol out of sight. “If you think you’ll be tempted by having alcohol in the house, put it away or give it to a friend to temporarily hold,” suggests Sheinbaum. As she notes, the point of a dry challenge isn’t to torture you. “It’s to make a dry month as simple, easy and as enjoyable as possible,” says Sheinbaum.
  • Sip tasty non-alcoholic beverages. “Replacing what is in your glass or cup doesn’t have to be fancy or require a lot of effort,”  Laing says. “Making a cup of soothing hot or iced tea, coffee or hot chocolate can be a helpful alternative, along with juices, smoothies, bubbly waters, and other beverages you have on hand that pique your interest.” Sheinbaum likes flavored seltzers, as well as Gruvi’s non-alcoholic prosecco and Athletic Brewing Company’s non-alcoholic beers. (For more inspiration, we’ve rounded up these delicious mocktail recipes.)


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