While you are sleeping, you are unconscious, but your brain and body functions are still active. Sleep is a complex biological process that helps you process new information, stay healthy, and feel rested.

During sleep, your brain cycles through five stages: stage 1, 2, 3, 4, and rapid eye movement (REM) sleep. Different things happen during each stage. For example, you have a different pattern of brain waves during each one. Your breathing, heart, and temperature may be slower or faster in some stages. Certain phases of sleep help you

• Feel rested and energetic the next day
• Learn information, get insight, and form memories
• Give your heart and vascular system a rest
• Release more growth hormone, which helps children grow. It also boosts muscle mass and the repair of cells and tissues in children and adults.
• Release sex hormones, which contributes to puberty and fertility
• Keep from getting sick or help you get better when you are sick, by creating more cytokines (hormones that help the immune system fight various infections)

You need all of the stages to get a healthy sleep.

Did you know that your body has its own internal network of clocks? These biological clocks help you feel alert during the day, hungry at mealtimes, and sleepy at night. Keeping your body’s daily cycles, or circadian rhythms, in sync is important for your health.

“Circadian rhythms are big influencers in the body,” explains NIH’s Dr. Michael Sesma, an expert in circadian biology. “They affect almost every part of your physiology in one way or another. Learning how the rhythm is generated is critical for understanding health.”

Our natural daily rhythms are synchronized with the sun. A “master clock” in the brain receives direct input from the eyes and coordinates all the biological clocks in the body. During the day, it sends signals to other brain regions to make hormones that will help keep you awake, boost your heart rate, and give you energy. In the evening, when less light enters your eyes, it triggers production of a hormone called melatonin. Melatonin makes you feel drowsy and helps you stay asleep.

“Many of your body’s functions and normal daily activities—like sleeping, waking, eating, and going to the bathroom—are patterned around this 24-hour cycle,” Sesma explains.

Your biological clock’s “settings” are determined by specific genes. These settings can affect body temperature, blood pressure, activity level, inflammation (your body’s protective response to injury or infection), fertility, mood, and brain functions. Even the timing of health-related events can be related to your biological clocks. For instance, heart attacks are more likely to occur early in the morning, when the level of a hormone called cortisol starts its daily rise.

Circadian rhythms can influence eating habits, digestion, and metabolism (how our body uses and stores energy), too. Researchers have found that eating later in the day, closer to when melatonin is released, can disrupt the body’s natural rhythms. This can lead to increased body fat and weight gain, which are often associated with obesity, heart disease, and diabetes.

Time of day has also been shown to impact the effectiveness and side effects of certain medications, including those used to treat cancer.

Be mindful about how you may be altering your circadian rhythms. “Our around-the-clock society creates challenges for our internal clocks,” Sesma says. “There are lots of modern situations that can disrupt our rhythms, and some may contribute to health problems.”

For instance, shift workers who must be on the job after the sun goes down are at odds with their biological clocks. They may be tired at work and have trouble falling or staying asleep during daylight hours after work. Studies show that shift workers have increased risk for heart disease, digestive disturbances, cancer, depression, and other health problems.

Traveling across time zones can also disrupt your circadian rhythms. The brain has trouble adjusting when the time of day suddenly changes. The result is jet lag.

“Researchers are considering time of day and how to sync up with the body’s clocks in all aspects of health, even the best time to have surgery on specific parts of the body,” Sesma says. These studies may lead to new insights for a range of clock-related disorders, from insomnia and jet lag to diabetes.

Keep Your Inner Clocks on Track

• Stick to a regular sleep schedule every day of the week.
• Sleep in a dark, quiet, and comfortable place.
• Avoid heavy meals two to three hours before bedtime.
• Avoid caffeine, nicotine, and alcohol late in the day.
• Exercise daily, but not within two hours of bedtime.
• Limit the use of electronics with bright screens before bedtime.

The amount of sleep you need depends on several factors, including your age, lifestyle, health, and whether you have been getting enough sleep recently. The general recommendations for sleep are

• Newborns: 16-18 hours a day
• Preschool-aged children: 11-12 hours a day
• School-aged children: At least 10 hours a day
• Teens: 9-10 hours a day
• Adults (including older adults): 7-8 hours a day

During puberty, teenagers' biological clocks shift, and they are more likely to go to bed later than younger children and adults, and they tend to want to sleep later in the morning. This delayed sleep-wake rhythm conflicts with the early-morning start times of many high schools and helps explain why most teenagers do not get enough sleep.

Some people think that adults need less sleep as they age. But there is no evidence to show that older adults can get by with less sleep than people who are younger. As people age, however, they often get less sleep or they tend to spend less time in the deep, restful stage of sleep. Older adults are also more easily awakened.

And it's not just the number of hours of sleep you get that matters. The quality of the sleep you get is also important. People whose sleep is frequently interrupted or cut short might not get enough of certain stages of sleep.

If you are wondering whether you are getting enough sleep, including quality sleep, ask yourself

• Do you have trouble getting up in the morning?
• Do you have trouble focusing during the day?
• Do you doze off during the day?

If you answered yes to these three questions, you should work on improving your sleep.

Instructions: In your current, usual way of life, how likely are you to nod off or fall asleep in the following situations, in contrast to feeling just tired? Even if you haven’t done some of these things recently, try to work out how they would affect you. It is important that you answer each question as best you can.

Using the following scale, choose the most appropriate number for each situation.

We have so many demands on our time—jobs, family, errands—not to mention finding some time to relax. To fit everything in, we often sacrifice sleep. But sleep affects both mental and physical health. It’s vital to your well-being.

Of course, sleep helps you feel rested each day. But while you’re sleeping, your brain and body don’t just shut down. Internal organs and processes are hard at work throughout the night.

“Sleep services all aspects of our body in one way or another: molecular, energy balance, as well as intellectual function, alertness and mood,” says Dr. Merrill Mitler, a sleep expert and neuroscientist at NIH.

When you’re tired, you can’t function at your best. Sleep helps you think more clearly, have quicker reflexes and focus better. “The fact is, when we look at well-rested people, they’re operating at a different level than people trying to get by on 1 or 2 hours less nightly sleep,” says Mitler.

“Loss of sleep impairs your higher levels of reasoning, problem-solving and attention to detail,” Mitler explains. Tired people tend to be less productive at work. They’re at a much higher risk for traffic accidents. Lack of sleep also influences your mood, which can affect how you interact with others. A sleep deficit over time can even put you at greater risk for developing depression.

But sleep isn’t just essential for the brain. “Sleep affects almost every tissue in our bodies,” says Dr. Michael Twery, a sleep expert at NIH. “It affects growth and stress hormones, our immune system, appetite, breathing, blood pressure and cardiovascular health.”

Research shows that lack of sleep increases the risk for obesity, heart disease and infections. Throughout the night, your heart rate, breathing rate and blood pressure rise and fall, a process that may be important for cardiovascular health. Your body releases hormones during sleep that help repair cells and control the body’s use of energy. These hormone changes can affect your body weight.

“Ongoing research shows a lack of sleep can produce diabetic-like conditions in otherwise healthy people,” says Mitler.

Recent studies also reveal that sleep can affect the efficiency of vaccinations. Twery described research showing that well-rested people who received the flu vaccine developed stronger protection against the illness.

A good night’s sleep consists of 4 to 5 sleep cycles. Each cycle includes periods of deep sleep and rapid eye movement (REM) sleep, when we dream. “As the night goes on, the portion of that cycle that is in REM sleep increases. It turns out that this pattern of cycling and progression is critical to the biology of sleep,” Twery says.

Although personal needs vary, on average, adults need 7 to 8 hours of sleep per night. Babies typically sleep about 16 hours a day. Young children need at least 10 hours of sleep, while teenagers need at least 9 hours. To attain the maximum restorative benefits of sleep, getting a full night of quality sleep is important, says Twery.

Sleep can be disrupted by many things. Stimulants such as caffeine or certain medications can keep you up. Distractions such as electronics—especially the light from TVs, cell phones, tablets and e-readers—can prevent you from falling asleep.

As people get older, they may not get enough sleep because of illness, medications or sleep disorders. By some estimates, about 70 million Americans of all ages suffer from chronic sleep problems. The 2 most common sleep disorders are insomnia and sleep apnea.

People with insomnia have trouble falling or staying asleep. Anxiety about falling asleep often makes the condition worse. Most of us have occasional insomnia. But chronic insomnia—lasting at least 3 nights per week for more than a month—can trigger serious daytime problems such as exhaustion, irritability and difficulty concentrating.

Common therapies include relaxation and deep-breathing techniques. Sometimes medicine is prescribed. But consult a doctor before trying even over-the-counter sleep pills, as they may leave you feeling unrefreshed in the morning.

People with sleep apnea have a loud, uneven snore (although not everyone who snores has apnea). Breathing repeatedly stops or becomes shallow. If you have apnea, you’re not getting enough oxygen, and your brain disturbs your sleep to open your windpipe.

Apnea is dangerous. “There’s little air exchange for 10 seconds or more at a time,” explains Dr. Phyllis Zee, a sleep apnea expert at Northwestern University. “The oxygen goes down and the body’s fight or flight response is activated. Blood pressure spikes, your heart rate fluctuates and the brain wakes you up partially to start your breathing again. This creates stress.”

Apnea can leave you feeling tired and moody. You may have trouble thinking clearly. “Also, apnea affects the vessels that lead to the brain so there is a higher risk of stroke associated with it,” Zee adds.

If you have mild sleep apnea, you might try sleeping on your side, exercising or losing weight to reduce symptoms. A CPAP machine, which pumps air into your throat to keep your airway open, can also help. Another treatment is a bite plate that moves the lower jaw forward. In some cases, however, people with sleep apnea need surgery.

“If you snore chronically and wake up choking or gasping for air, and feel that you’re sleepy during the day, tell your doctor and get evaluated,” Zee advises.

NIH is currently funding several studies to gain deeper insights into sleep apnea and other aspects of sleep. One 5-year study of 10,000 pregnant women is designed to gauge the effects of apnea on the mother’s and baby’s health. Zee says this study will shed more light on apnea and the importance of treatment.

Good sleep is critical to your health. To make each day a safe, productive one, take steps to make sure you regularly get a good night’s sleep.

Getting Quality Sleep

• Go to bed the same time each night and get up the same time each morning.
• Sleep in a dark, quiet, comfortable environment.
• Exercise daily (but not right before bedtime).
• Limit the use of electronics before bed.
• Relax before bedtime. A warm bath or reading might help.
• Avoid alcohol and stimulants such as caffeine late in the day.
• Avoid nicotine.
• Consult a health care professional if you have ongoing sleep problems.

Sleep is important for overall health. When you don't get enough sleep (sleep deprivation), it does more than just make you feel tired. It can affect your performance, including your ability to think clearly, react quickly, and form memories. This may cause you to make bad decisions and take more risks. People with sleep deprivation are more likely to get into accidents.

Sleep deprivation can also affect your mood, leading to

• Irritability
• Problems with relationships, especially for children and teenagers
• Depression
• Anxiety

It can also affect your physical health. Research shows that not getting enough sleep, or getting poor-quality sleep, increases your risk of

• High blood pressure
• Heart disease
• Stroke
• Kidney disease
• Obesity
• Type 2 diabetes

Not getting enough sleep can also mean that you don't get enough of the hormones that help children grow and help adults and children build muscle mass, fight infections, and repair cells.

Sleep deprivation magnifies the effect of alcohol. A tired person who drinks too much alcohol will be more impaired than a well-rested person.

You can take steps to improve your sleep habits. First, make sure that you allow yourself enough time to sleep. With enough sleep each night, you may find that you're happier and more productive during the day.

To improve your sleep habits, it also may help to

• Go to bed and wake up at the same time every day
• Avoid caffeine, especially in the afternoon and evening
• Avoid nicotine
• Exercise regularly, but don't exercise too late in the day
• Avoid alcoholic drinks before bed
• Avoid large meals and beverages late at night
• Don't take a nap after 3 p.m.
• Relax before bed, for example by taking a bath, reading or listening to relaxing music
• Keep the temperature in your bedroom cool
• Get rid of distractions such as noises, bright lights, and a TV or computer in the bedroom. Also, don't be tempted to go on your phone or tablet just before bed.
• Get enough sunlight exposure during the day
• Don't lie in bed awake; if you can't sleep for 20 minutes, get up and do something relaxing
• See a doctor if you have continued trouble sleeping. You may have a sleep disorder, such as insomnia or sleep apnea. In some cases, your doctor may suggest trying over-the-counter or prescription sleep aid. In other cases, your doctor may want you to do a sleep study, to help diagnose the problem.

If you are a shift worker, it can be even harder to get a good sleep. You may also want to

• Take naps and increase the amount of time available for sleep
• Keep the lights bright at work
• Limit shift changes so your body clock can adjust
• Limit caffeine use to the first part of your shift
• Remove sound and light distractions in your bedroom during daytime sleep (for example, use light-blocking curtains)

Getting enough sleep is important for good health and well-being. The amount of sleep you need changes as you age, and sleep needs vary from person to person. Most adults need to sleep seven or more hours each night. Not getting enough sleep can lead to physical and mental health problems.

Healthy sleep involves not only getting enough hours of sleep, but sleeping at the right time of day and having good quality sleep. Good quality sleep means that you’ve gotten enough of two different phases of sleep: rapid eye movement (REM)—the deep sleep in which dreaming happens—and non-REM. You may not be getting quality sleep if you don’t feel rested after you’ve slept enough, you repeatedly wake up during the night, or you experience symptoms of sleep disorders, like snoring or gasping for air.

Previous studies have led to the identification of over 50 families with people who need less than six and a half hours of sleep a night to feel well rested. To better understand why some people need much less sleep than most, a team led by Dr. Ying-Hui Fu and Dr. Louis Ptáček at the University of California, San Francisco carried out a study in a family with three generations of naturally short sleepers to look for genes involved in their unusual sleep patterns. The research was supported in part by NIH’s National Institute of Neurological Disorders and Stroke (NINDS). Results were published online on August 28, 2019, in Neuron.

Using whole exome genome sequencing, the researchers searched for gene mutations that only the naturally short sleepers had. They found a rare mutation in the ADRB1 gene that was being passed through the family. Family members who inherited one copy of this mutant gene had a shortened sleep cycle. The ADRB1 gene codes for the β1-adrenergic receptor. Adrenergic receptors are found on many cells in the body and respond to hormones, including those known to regulate the sleep/wake cycle.

The researchers found that certain brain cells expressed high levels of the β1-adrenergic receptor. These cells were located in a brain region that’s involved in regulating sleep behaviors called the dorsal pons. The brain cells were active when mice were in REM sleep or awake, but not during non-REM sleep.

To learn more about the mutation’s effects in the brain, the researchers created genetically engineered mice with the altered gene. Mice with the genetic mutation slept almost an hour less each day than normal mice. They had about seven minutes less of REM sleep and 53 minutes less of non-REM sleep.

Brain cells with the ADRB1 mutation showed altered activity and electrophysiological properties, making them more easily activated. Mice with the mutation showed increased activity of brain cells with the β1-adrenergic receptor compared with normal mice.

When researchers turned on brain cells with the β1-adrenergic receptor during non-REM sleep using a light-activated protein, the mice woke up. These results suggest that increased activity of wake-promoting brain cells may be one of the mechanisms underlying naturally shorter sleep cycles.

“Sleep is complicated,” Ptáček explains. “We don’t think there’s one gene or one region of the brain that’s telling our bodies to sleep or wake. This is only one of many parts.”

“Natural short sleepers experience better sleep quality and sleep efficiency,” Fu says. “By studying them, we hope to learn what makes for a good night's sleep, so that all of us can be better sleepers leading happier, healthier lives.”

—by Tianna Hicklin, Ph.D.