We do it every night, and over the course of our life we will spend approximately a third of our time doing it: sleep. But what is it? Doctors and scientists are really just beginning to understand all the important ways that sleep affects our health and well-being — and all the reasons why we do it.
According to Rafael Pelayo, MD, a clinical professor of psychiatry and behavioral sciences and a sleep specialist at the Stanford Sleep Medicine Center in Redwood City, California, “Sleep is a natural, restorative physiological process characterized by a perceptual disengagement [in which you tune out from whatever’s going on around you], and must be rapidly reversible.”
The bottom line is that we need sleep to function, Dr. Pelayo says. It’s a critical process that allows the body to function and stay healthy — and it’s especially important for the brain.
That means inadequate sleep or poor quality sleep will damage many systems of the body and over time can contribute to a greater risk of chronic disease and health problems. But the most immediate consequences of not sleeping that you’ll notice are those that affect your mind and thinking.
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Why Sleep Is So Important for Your Health
We intuitively know we need sleep. When you don’t get a good night’s sleep, you’ll likely feel drowsy, you won’t quite be able to think as clearly as usual, and you might be moody and irritable. That’s because one of the key functions of sleep is to restore the brain.
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Why the Brain Needs Sleep
You likely won’t be measuring your daily ATP levels, but they do affect your ability to function in big ways. If you don’t get a good night’s sleep and those chemical processes don’t happen, the next day you’ll likely notice:
- It’s tougher to concentrate.
- It’s harder to remember things.
- You’re moody and irritable.
- Your judgment might be skewed.
- You have less patience.
- You’re more likely to make rash decisions or have a tough time making decisions.
- You’re more emotional than usual.
- Your hand-eye coordination is a little bit off.
Why the Body Needs Sleep
Over time, chronic poor sleep has been linked to worse heart health. So much evidence points to this that the American Heart Association updated its checklist of modifiable factors linked to cardiovascular health in June 2022 to include sleep. The list also includes diet, exercise, tobacco use, weight, cholesterol, blood sugar levels, and blood pressure, and is published in the journal Circulation.
- Type 2 diabetes
- Heart disease and hypertension
- Depression, anxiety, and other mood disorders
- Poor immune function
- Earlier death
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Circadian Rhythm, Sleep Stages, and Sleep Cycles: Everything You Need to Know About What Happens When You Sleep
You may not remember everything that happens each night when you’re asleep, but if you’re doing it right, there’s a lot going on in your brain and your body, Pelayo says. “There are differences between sleep and awake for every single body system, but nothing as dramatic as the changes of consciousness during sleep,” he says.
The Different Stages of Sleep
Stage 2: Non-REM sleep In the second stage, your heart rate drops and your body temperature falls even more. Eye movement stops completely and your brain slows way down, except for brief bursts of activity.
Stage 3: Non-REM sleep Next comes deep sleep. This stage is heavy and restorative. Your heartbeat and breathing slow down the most during this type of sleep, and now is the time when it's hardest to awake.
Learn More About the Sleep Cycles and the Stages of Sleep
What Drives Sleep
Then there’s our circadian rhythm, our body’s biological clock, which syncs our body functions with environmental cues. These internal clocks are what drive us to feel sleepy at night and more awake in the morning (even, for instance, if you slept poorly the previous night, or pulled an all-nighter). They’re regulated by hormones, such as the stress hormone cortisol and the sleep hormone melatonin, which get secreted by the brain to send these wake and sleep signals to the body.
“They’re two complementary systems in the brain,” Pelayo says. And when there’s a discrepancy between the homeostatic drive to sleep and the signal to sleep that comes from the circadian system, problems like jet lag and other disordered sleep occur.
“This is why people who wake up at different times every day may feel tired a lot,” Pelayo says. “The brain doesn’t know how to predict when they should be awake. It’s like being constantly jet-lagged.”
The more sleep researchers learn about these two systems that control sleep, the more it is clear why not only sufficient hours of sleep, but also good sleep habits (such as going to sleep and waking up at the same time each day) are important.
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How Much Sleep You Actually Need
That recommendation, along with additional recommended sleep times for younger children, adolescents, and older adults, is based on the amount of sleep associated with the best health outcomes in a number of areas, including things like mood, learning, accidents, hypertension, heart disease, diabetes, and pain.
But Pelayo says not to get too concerned about banking a specific number of hours of sleep each night. “The issue is waking up refreshed,” he says. “You should never wake up tired. If you do wake up feeling tired, something is wrong.”
Waking up sleepy may indicate that the quality of your sleep is poor. Maybe you’re spending too much time in light sleep and not getting enough restorative deep sleep, for example, Pelayo says. If that’s the case, you should ask your doctor about getting checked for a sleep disorder, or see a sleep medicine specialist.
Common Sleep Disorders
Everyone should be able to get a good night’s sleep on a regular basis, Pelayo says. And if you’re not (and it’s not because you lack the opportunity to sleep), it’s important to be aware of the several sleep disorders that might be interfering with your rest.
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Obstructive sleep apnea (OSA) Obstructive sleep apnea, or “sleep apnea” for short, is a disorder in which a person's airway becomes partially or completely blocked during sleep, causing the person to repeatedly wake up and preventing the deep, restorative sleep they need. People who are obese, have a small jaw or a large overbite, or use alcohol before bed are all at a higher risk for sleep apnea.
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If you snore or wake up still feeling tired, particularly after a full night asleep, you may have sleep apnea and should get checked out by your doctor. Left untreated, sleep apnea can cause big problems, including high blood pressure, heart disease, memory problems, and higher accident risk.
None of these problems should be left unaddressed, Pelayo says. If you suspect you may have one of these conditions, it’s important to get checked out and treated.
How to Sleep Better Tonight
There’s no silver bullet formula for getting a good night’s sleep, but there are several steps you can take that have been associated with better sleep overall if you’re struggling to clock the recommended number of hours you know you need — or if you wake up less perky than you'd like to be.
It’s important to check with your doctor or a sleep medicine specialist if you think you have a more serious problem, or if another medical condition is interfering with your sleep.
But trying these fixes is a fine place to start.
Stick to a consistent sleep-wake schedule. Aim to go to bed at the same time each night and wake up at the same time in the morning, including on the weekends — and try not to vary it by more than an hour or so. The times that you regularly go to bed and wake up are the signals you give your body’s natural clock, and when they’re consistent, that clock helps you wake up and fall asleep. If those signals are out of whack, your body clock gets thrown off and you experience the same drowsiness associated with jet lag. You also may struggle to fall asleep at night or wake up when your alarm rings.
Watch caffeine intake. Be especially careful with this later in the afternoon. Pelayo suggests avoiding caffeine within six hours of when you want to sleep.
If you can’t sleep, don’t linger in bed. This means at night if you’re having trouble falling asleep for 20 minutes or longer, get out of bed and do something to make you tired, such as reading or some gentle stretching. Staying in bed makes your body associate in-bed time as awake time, and it will actually be harder to fall asleep.
Don’t linger in bed in the morning either, and don’t hit snooze. It can be tempting to wake up slowly, but that drowsy sleep (after you’ve initially woken up) is fragmented, light sleep. If you did get a poor night’s sleep, your best remedy is getting up, going about your day, and hitting your pillow at bedtime that evening, at which point your sleep drive will be strong and you’re more likely to actually reap the benefit of the deep restorative sleep you need.
Resources We Love
Whether you’re trying to improve your sleep or need to learn more about various sleep disorders, here are some dreamy sleep resources.
American Sleep Apnea Association
If you’ve just been diagnosed with sleep apnea, connect with this association. It includes resources, such as a CPAP Mentor program, matching you with an experienced sleep apnea patient, a CAP Mask program, which provides equipment to those who can’t afford it, and a library of webinars and podcasts about living with sleep apnea.
This nonprofit is all about raising awareness of sleep health and sleep disorders. Learn more about the benefits of sleep, common sleep disorders, and how to find a sleep center near you. Project Sleep runs a slate of programs, including the Jack and Julie Narcolepsy Scholarship supporting students with narcolepsy and hypersomnia, and the Rising Voices of Narcolepsy program, helping the next generation of narcolepsy patient-advocates spread awareness about the sleep condition.
Founded in 1986, this longtime national nonprofit provides emotional support and resources to patients, family members, and friends. It includes the latest clinical research on narcolepsy, support groups for various age groups, and details on sleep centers and narcolepsy specialists across the country.
Restless Legs Syndrome Foundation
Established in 1992, this nonprofit is home to science-based education and patient services to help people living with the syndrome. It claims to be the only organization with a dedicated grant program to advance research for new treatments and a cure for restless legs syndrome.
SLEEP is the international journal of sleep and circadian science. If you want to read the latest peer-reviewed research and commentaries, or look up existing research on specific sleep disorders, it has a vast collection of papers to browse through. Topics include circadian disorders, insomnia, sleep and metabolism, and the neuroscience of sleep.
Established by the American Academy of Sleep Medicine, this website has a bedtime calculator, sleep diaries, and explainers on dozens of sleep disorders, including sleep-wake disorders, hypersomnias, parasomnias, breathing disorders, and movement disorders.
Created by the clinical psychologist and American Academy of Sleep Medicine Fellow Michael Breus, PhD, this website calls itself “your ultimate sleep resource center.” It includes tips on how to sleep better, doctor-recommended products to help with your slumber, and sleep quizzes developed by Dr. Breus to help you figure out your sleep chronotype.
If you’re sleep training your little ones, make sure to bookmark this website on your browser. Kim West, LCSW, offers parents with newborns to 6-year-olds sleep tips, including how to handle nightmares and napping and how to develop a sleep schedule for every age and life stage. She's also written a book aptly titled Good Night, Sleep Tight.
Editorial Sources and Fact-Checking
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