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Why Is Sleep Important?

Reviewed by Psychology Today Staff

Sleep is the balm that soothes and restores after a long day. Sleep is largely driven by the body’s internal clock, which takes cues from external elements such as sunlight and temperature. The body’s natural sleep-and-wake cycle is reasonably attuned to a 24-hour period.

Perturbations in the sleep cycle are disruptive to the functioning of many body systems. Learning, memory, stamina, general health, and mood are all affected by sleep duration and quality. For many people, sleep is elusive or otherwise troubled. In fact, most people, at some point in their lives, experience difficulty falling asleep or staying asleep. Potential consequences of consistently poor sleep include obesity, cardiovascular disease, and diabetes. Sleep deprivation can also affect judgement and mental acuity.

Sleep needs differ from person to person and across different age groups. One person may need eight full hours, while another can function with less sleep. The good news is that the treatment of sleep disorders is rapidly progressing.

Why do we sleep?
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Despite the universal need for sleep, there remains much about it that scientists don’t understand. It is known that sleep allows for the body and brain to replenish energy and repair themselves in critical ways. Memory consolidation, information processing, physical growth, muscle repair, and countless other processes are theorized to occur during sleep; sleep is also critical for strengthening the immune system and allowing the body to fight off disease.

To learn more about the benefits of sleep, see Sleep and Mental Health or Sleep and Physical Health.

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How much sleep do I need?

Sleep needs vary by age, and variation exists even within age groups. But in general, The National Sleep Foundation provides these daily sleep guidelines:

  • Infants (4-11 months): 12-15 hours
  • School-age children (6-13): 9-11 hours
  • Teenagers (14-17): 8-10 hours
  • Young adults (18-25): 7-9 hours
  • Adults (26-64): 7-9 hours
  • Older adults (65+): 7-8 hours

To learn more about how sleep needs change over time, see Children and Sleep.

How long should it take me to fall asleep?
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In general, it should take about 10 to 20 minutes for a person to drift off. But if one perceives that it is taking too long—whether it takes 20 minutes or an hour—that can spur anxiety about sleep that negatively affects sleep quality. Falling asleep as soon as one's head hits the pillow is not proof that one is a good sleeper; it's more likely an indication that an individual is sleep-deprived.

For more on recognizing signs of disordered sleep, see Overcoming Insomnia or Sleep Disorders.

Do some people need more sleep than others?

Absolutely. Some people may feel great after 7 hours of sleep, while others don’t feel rested unless they get a solid 9. There do appear to be rare individuals who can function on significantly less sleep, which evidence suggests is due to genetics; conversely, there appear to be some people who require significantly longer amounts of sleep—up to 10 hours a night—to function optimally.

Am I a “short sleeper”?
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“Short sleepers”—or those who are genetically programmed to require less sleep than average—do exist, and are thought to make up approximately 5 percent of the population. However, many people who think they are functioning well on little sleep may actually be chronically sleep deprived, as evidence suggests that it becomes difficult for people to objectively judge their mental state after several nights of poor sleep.

How can I get better sleep?
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The standard sleep hygiene advice can be of great help to many poor sleepers: Make sure your bedroom is cool and dark. Use your bed only for sex and sleep. Avoid caffeine from mid-afternoon on. And avoid all screens for at least an hour before turning in; screens' melatonin-inhibiting blue light delays sleep latency by an average of 10 minutes. Falling asleep in front of a TV, as 61 percent of adults confess to having done, is a problem as well: The screen's light penetrates the eyelids, so the brain still experiences exposure to light. This phenomenon prevents the more refreshing stages of deep sleep.

For more on improving sleep, see How to Sleep Better.

What is the purpose of dreams?

Researchers still aren’t entirely sure, but theories abound. Some experts hypothesize that dreams and nightmares—which often consist, at least in part, of real people, places, and life events—help the brain consolidate memories accumulated over the course of the day, identifying which ones to retain for long-term memory and allowing the rest to fade. Others argue that dream scenarios allow us to process emotions, mull over problems, or act out fantasies in a safe environment. Regardless of their purpose, what is known about dreams is that they appear to be universal—even if some people almost never remember having them.

For more about dreams, see Understanding Dreams or Managing Nightmares.

What is a chronotype?
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The word “chronotype” refers to an individual’s preferred sleep/wake schedule, based on their biologically programmed circadian rhythm. The most well-known chronotypes are “night owls”—or those who prefer to stay up late into the evening and awaken later in the day—and “morning larks,” who lean toward an “early to bed, early to rise” schedule. Chronotypes exist on a spectrum; while a few people are at either extreme, the majority of people fall somewhere in the middle.

How do I find out my chronotype?
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Most people discover their chronotype by a process of trial and error; they naturally gravitate toward a specific sleep schedule and feel “off” when that schedule is interrupted. For those who are unsure, there also exist online quizzes that purport to help individuals understand their chronotype.

What is “sleep debt”?

The term “sleep debt” refers to the difference between the amount of sleep someone needs and the amount of sleep they actually get; someone whose body requires 8 hours of sleep per night, for instance, but only gets 6, would accumulate a 14-hour sleep debt over the course of a week. Accumulating a large sleep debt has been associated with increased risk of certain physical and mental health conditions such as diabetes or anxiety.

For more on tackling insufficient sleep, see Overcoming Insomnia.

Should I replace my mattress?
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An old or poor-quality mattress may be hindering sleep quality. The Better Sleep Council states that mattresses should be replaced every 7 to 10 years; older ones tend to stop providing adequate support, resulting in restless, inadequate sleep; they also accumulate allergens which can further disrupt sleep.

What devices can help me sleep?
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Many sleep experts endorse the use of weighted blankets, and not just for those with conditions like restless leg syndrome. Users find that the blankets provide the same type of comfort as hugs or swaddling for babies. Wearing a sleep-tracking bracelet that can record when one falls asleep and wakes up, and detect interrupted sleep, can also help some people. Ironically, its primary benefit may be providing reassurance to those who believe they’re getting hardly any sleep—a phenomenon known as paradoxical insomnia.

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