Sleep, Importance of an Important Life Process
Adequate sleep allows your body and brain to sustain a healthy mental, physical, cognitive, and emotional existence.
Sleep is a period of rest that alternates with wakefulness. You have internal body clocks that control when you are awake and when your body is ready for sleep. These clocks have cycles of approximately 24 hours. The watches are regulated by multiple factors, including light, darkness, and sleep schedules. Once asleep, you cycle through sleep stages throughout the night in a predictable pattern.
Sleep is an essential part of your daily routine—you spend about one-third of your time doing it. Sleep is important because it affects many of your body’s systems. Not getting enough sleep or enough quality sleep raises your risk for heart and respiratory problems and affects your metabolism and ability to think clearly and focus on tasks.
Without sleep, you can’t form or maintain the pathways in your brain that let you learn and create new memories, and it’s harder to concentrate and respond quickly.
Sleep is important to several brain functions, including how nerve cells (neurons) communicate. In fact, your brain and body stay remarkably active while you sleep. Recent findings suggest that sleep plays a housekeeping role that removes toxins in your brain that build up while you are awake.
Everyone needs sleep, but its biological purpose remains a mystery. Sleep affects almost every tissue and system in the body – from the brain, heart, and lungs to metabolism, immune function, mood, and disease resistance. Research shows that a chronic lack of sleep, or getting poor quality sleep, increases the risk of disorders including high blood pressure, cardiovascular disease, diabetes, depression, and obesity.
Sleep is a complex and dynamic process that affects how you function in ways scientists are now beginning to understand. This booklet describes how your need for sleep is regulated and what happens in the brain during sleep.
Your Sleep/Wake Cycle
Many factors play a role in preparing your body to fall asleep and wake up. Your body has several internal clocks, called circadian clocks. These typically follow a 24-hour repeating rhythm, called the circadian rhythm. This rhythm affects every cell, tissue, and organ in your body and how they work. Learn more in our Circadian Rhythms Disorders Health Topic.
Your central circadian clock, located in your brain, tells you when it is time for sleep. Other circadian clocks are located in organs throughout your body. Your body’s internal clocks are in sync with certain cues in the environment. Light, darkness, and other cues help determine when you feel awake and when you feel drowsy. Artificial light and caffeine can disrupt this process by giving your body false wakefulness cues
Your body has a biological need for sleep that increases when you have been awake for a long time. This is controlled by homeostasis, the process by which your body keeps your systems, such as your internal body temperature, steady. A compound called adenosine is linked to this need for sleep. While you are awake, the level of adenosine in your brain continues to rise. The rising levels signal a shift toward sleep. Caffeine and certain drugs can interrupt this process by blocking adenosine.
Stages of Sleep
When you sleep, you cycle through two phases of sleep: rapid eye movement (REM) and non-REM sleep. The cycle starts over every 80 to 100 minutes. Usually, there are four to six cycles per night. You may wake up briefly between cycles. Sleep studies use sensors to record eye movements and brain activity, which classify sleep phases and stages.
During REM sleep, your eyes twitch, and your brain is active. Brain activity measured during REM sleep is similar to your brain’s activity during waking hours. Dreaming usually happens during REM sleep. Your muscles naturally become limp to prevent you from acting out your dreams. You typically have more REM sleep later in the night, but you do not have as much REM sleep in colder temperatures. This is because, during REM sleep, your body does not regulate its temperature properly.
How do our patterns of sleep change as we age?
The patterns and types of sleep change as people mature. For example, newborns spend more time in REM sleep. The amount of slow-wave sleep peaks in early childhood and then drops sharply in the teenage years. Slow-wave sleep continues to decrease through adulthood, and older people may not have any slow-wave sleep at all.
Importance of Sleep
Sleep plays a vital role in good health and wellbeing throughout your life. The way you feel while you are awake depends on what happens while you are sleeping. During sleep, your body supports healthy brain function and maintains your physical health. In children and teens, sleep also helps support growth and development. Getting inadequate sleep over time can raise your risk for chronic health problems. It can also affect how well you think, react, work, learn, and get along with others. Learn how sleep affects your heart and circulatory system, metabolism, respiratory system, and immune system and how much sleep is enough.
When you fall asleep and enter non-REM sleep, your blood pressure and heart rate fall. During sleep, your parasympathetic system controls your body, and your heart does not work as hard as it does when you are awake. During REM sleep and when waking, your sympathetic system is activated, increasing your heart rate and blood pressure to the normal levels when you are awake and relaxed. A sharp increase in blood pressure and heart rate upon waking has been linked to angina and heart attacks.
People who do not sleep enough or wake up frequently may have a higher risk of:
Your body makes different hormones at different times of the day. This may be related to your sleep pattern or your circadian clocks. In the morning, your body releases hormones that promote alertness, such as cortisol, which helps you wake up. Other hormones have 24-hour patterns that vary throughout your life; for example, in children, the hormones that tell the glands to release testosterone, estrogen, and progesterone are made in pulses at night, and the pulses get bigger as puberty approaches.
The way your body handles fat varies according to various circadian clocks, including those in the liver, fat, and muscle. For example, the circadian clocks make sure that your liver is prepared to help digest fats at appropriate times. Your body may handle fat differently if you eat at unusual times.
Studies have shown that not getting enough quality sleep can lead to:
- Increased levels of hormones that control hunger, including leptin and ghrelin, inside your body
- Decreased ability to respond to insulin
- Increased consumption of food, especially fatty, sweet, and salty foods
- Decreased physical activity
- Metabolic syndrome
All of these contribute to overweight and obesity.
You breathe less often and less deeply during sleep and take in less oxygen. These changes can cause problems in people with health problems such as asthma or chronic obstructive pulmonary disease (COPD). Asthma symptoms are usually worse during early morning sleep. Likewise, breathing problems in people who have lung diseases such as COPD can worsen during sleep.
Sleep also affects different parts of your immune system, which become more active at different times of the day. For example, when you sleep, a particular type of immune cell works harder. That is why people who do not sleep enough may be more likely to get colds and other infections.
Sleep helps with learning and the formation of long-term memories. Not getting enough sleep or enough high-quality sleep can lead to problems focusing on tasks and thinking clearly. Read our Sleep Deprivation and Deficiency Health Topic for more information on how lack of sleep affects daily activities’ performance, including driving and schoolwork.
Sleep promotes your overall wellbeing. Try approaching an interview, test, or important meeting without a good night’s sleep. See how your comprehensive self is depleted and how focus, concentration, problem-solving, memory decision-making, and lean ability are reduced by sacrificing a good night’s sleep.
How Much Sleep is Enough?
Experts recommend that adults sleep between 7 and 9 hours a night. Adults who sleep less than 7 hours a night may have more health issues than those who sleep 7 or more hours a night. Sleeping more than 9 hours a night is not necessarily harmful and may help young adults, people who are recovering from sleep deprivation, and sick people.
How much sleep children should get depends on their age. Sleep experts consider naps to be appropriate for children under age 7. Below you can find the recommended hours of sleep, including naps, for different ages.
- For newborns younger than 4 months, sleep patterns vary widely.
- Babies 4 months to 1 year old should sleep 12 to 16 hours per day.
- Children 1 to 2 years old should sleep 11 to 14 hours per day.
- Children 3 to 5 years old should sleep 10 to 13 hours per day.
- Children 6 to 12 years old should sleep 9 to 12 hours per day.
- Teens 13 to 18 years old should sleep 8 to 10 hours per day.
- Adults 18 to 60 years should sleep 7 or more hours per day.
- Adults 61 to 64 years should sleep 7 to 9 hours per day.
- Adults 65 years and older should sleep 7 to 8 hours per day.
Talk to your doctor or your child’s doctor if you think you or your child is sleeping too much or too little.
Why Sleep is Important and What Happens When You Don't Get Enough?
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