Many factors play a role in preparing your body to fall asleep and wake up. You have an internal "body clock" that controls when you're awake and when your body is ready for sleep.
The body clock typically has a 24-hour repeating rhythm (called the circadian rhythm). Two processes interact to control this rhythm. The first is a pressure to sleep that builds with every hour that you're awake. This drive for sleep reaches a peak in the evening, when most people fall asleep.
A second process involves your internal body clock. This clock is in sync with certain cues in the environment. Light, darkness, and other cues help determine when you feel awake and when you feel drowsy.
For example, light signals received through your eyes tell a special area in your brain that it is daytime. This area of your brain helps align your body clock with periods of the day and night.
Your body releases chemicals in a daily rhythm, which your body clock controls. When it gets dark, your body releases a hormone called melatonin (mel-ah-TONE-in). Melatonin signals your body that it's time to prepare for sleep, and it helps you feel drowsy.
The amount of melatonin in your bloodstream peaks as the evening wears on. Researchers believe this peak is an important part of preparing your body for sleep.
Exposure to bright artificial light in the late evening can disrupt this process, making it hard to fall asleep. Examples of bright artificial light include the light from a TV screen, computer screen, or a very bright alarm clock.
As the sun rises, your body releases cortisol (KOR-tih-sol). This hormone naturally prepares your body to wake up.
The rhythm and timing of the body clock change with age. Teens fall asleep later at night than younger children and adults. One reason for this is because melatonin is released and peaks later in the 24-hour cycle for teens. As a result, it's natural for many teens to prefer later bedtimes at night and sleep later in the morning than adults.
People also need more sleep early in life, when they're growing and developing. For example, newborns may sleep more than 16 hours a day and preschool-aged children need to take naps.
Young children tend to sleep more in the early evening. Teens tend to sleep more in the morning. Also, older adults tend to go to bed earlier and wake up earlier.
The patterns and types of sleep also change as people mature. For example, newborn infants spend more time in REM sleep. The amount of slow-wave sleep (a stage of non-REM sleep) peaks in early childhood and then drops sharply after puberty. It continues to decline as people age.
Sleep plays a vital role in good health and well-being throughout your life. Getting enough quality sleep at the right times can help protect your mental health, physical health, quality of life, and safety.
The way you feel while you're awake depends in part on what happens while you're sleeping. During sleep, your body is working to support healthy brain function and maintain your physical health. In children and teens, sleep also helps support growth and development.
The damage from sleep deficiency can occur in an instant (such as a car crash), or it can harm you over time. For example, ongoing sleep deficiency can raise your risk for some chronic health problems. It also can affect how well you think, react, work, learn, and get along with others.
Sleep helps your brain work properly. While you're sleeping, your brain is preparing for the next day. It's forming new pathways to help you learn and remember information.
Studies show that a good night's sleep improves learning. Whether you're learning math, how to play the guitar, how to perfect your straight drive or how to drive a car, sleep helps enhance your learning and problem-solving skills. Sleep also helps you pay attention, make decisions, and be creative.
Studies also show that sleep deficiency alters activity in some parts of the brain. If you're sleep deficient, you may have trouble making decisions, solving problems, controlling your emotions and behavior, and coping with change. Sleep deficiency also has been linked to depression, suicide, and risk-taking behavior.
Children and teens that are sleep deficient may have problems getting along with others. They may feel angry and impulsive, have mood swings, feel sad or depressed, or lack motivation. They also may have problems paying attention, and they may get lower grades and feel stressed.
Sleep plays an important role in your physical health. For example, sleep is involved in healing and repair of your heart and blood vessels. Ongoing sleep deficiency is linked to an increased risk of heart disease, kidney disease, high blood pressure, diabetes, and stroke.
Sleep deficiency also increases the risk of obesity. For example, one study of teenagers showed that with each hour of sleep lost, the odds of becoming obese went up. Sleep deficiency increases the risk of obesity in other age groups as well.
Sleep helps maintain a healthy balance of the hormones that make you feel hungry (ghrelin) or full (leptin). When you don't get enough sleep, your level of ghrelin goes up and your level of leptin goes down. This makes you feel hungrier than when you're well-rested.
Sleep also affects how your body reacts to insulin, the hormone that controls your blood glucose (sugar) level. Sleep deficiency results in a higher than normal blood sugar level, which may increase your risk for diabetes.
Sleep also supports healthy growth and development. Deep sleep triggers the body to release the hormone that promotes normal growth in children and teens. This hormone also boosts muscle mass and helps repair cells and tissues in children, teens, and adults. Sleep also plays a role in puberty and fertility.
Your immune system relies on sleep to stay healthy. This system defends your body against foreign or harmful substances. Ongoing sleep deficiency can change the way in which your immune system responds. For example, if you're sleep deficient, you may have trouble fighting common infections.
Getting enough quality sleep at the right times helps you function well throughout the day. People who are sleep deficient are less productive at work and school. They take longer to finish tasks, have a slower reaction time, and make more mistakes.
After several nights of losing sleep—even a loss of just 1–2 hours per night—your ability to function suffers as if you haven't slept at all for a day or two.
Lack of sleep also may lead to micro sleep. Microsleep refers to brief moments of sleep that occur when you're normally awake.
You can't control microsleep, and you might not be aware of it. For example, have you ever driven somewhere and then not remembered part of the trip? If so, you may have experienced microsleep.
Even if you're not driving, microsleep can affect how you function. If you're listening to a lecture, for example, you might miss some of the information or feel like you don't understand the point. In reality, though, you may have slept through part of the lecture and not been aware of it.
Some people aren't aware of the risks of sleep deficiency. In fact, they may not even realize that they're sleep deficient. Even with limited or poor-quality sleep, they may still think that they can function well.
For example, drowsy drivers may feel capable of driving. Yet, studies show that sleep deficiency harms your driving ability as much as, or more than, being drunk.
Drivers aren't the only ones affected by sleep deficiency. It can affect people in all lines of work, including health care workers, pilots, students, lawyers, mechanics, and assembly line workers.
As a result, sleep deficiency is not only harmful on a personal level, but it also can cause large-scale damage. For example, sleep deficiency has played a role in human errors linked to tragic accidents, such as nuclear reactor meltdowns, grounding of large ships, and aviation accidents.
The amount of sleep you need each day will change over the course of your life. Although sleep needs vary from person to person, the chart below shows general recommendations for different age groups.
| Age | Recommended Amount of Sleep |
|---|---|
| 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 the elderly) | 7–8 hours a day |
If you routinely lose sleep or choose to sleep less than needed, the sleep loss adds up. The total sleep lost is called your sleep debt. For example, if you lose 2 hours of sleep each night, you'll have a sleep debt of 14 hours after a week.
Some people nap as a way to deal with sleepiness. Naps may provide a short-term boost in alertness and performance. However, napping doesn't provide all of the other benefits of night - time sleep. Thus, you can't really make up for lost sleep.
Some people sleep more on their days off than on work days. They also may go to bed later and get up later on days off.
Sleeping more on days off might be a sign that you aren't getting enough sleep. Although extra sleep on days off might help you feel better, it can upset your body's sleep – wake rhythm.
Bad sleep habits and long-term sleep loss will affect your health. If you're worried about whether you're getting enough sleep, try using a sleep diary for a couple of weeks.
Write down how much you sleep each night, how alert and rested you feel in the morning, and how sleepy you feel during the day. Show the results to your doctor and talk about how you can improve your sleep.
Sleeping when your body is ready to sleep also is very important. Sleep deficiency can affect people even when they sleep the total number of hours recommended for their age group.
For example, people whose sleep is out of sync with their body clocks (such as shift workers) or routinely interrupted (such as caregivers or emergency responders) might need to pay special attention to their sleep needs.
If your job or daily routine limits your ability to get enough sleep or sleep at the right times, talk with your doctor. You also should talk with your doctor if you sleep more than 8 hours a night, but don't feel well rested. You may have a sleep disorder or other health problem.