About Sleep

Sleep is a complex biological process that helps people process new information, stay healthy, and re-energize. Periods of sleep and wakefulness are part of how our bodies function.

Although you are resting while you sleep, your brain remains highly active. Sleep consists of different stages that repeat several times each night. During sleep, the brain cycles through two distinct phases: rapid eye movement (REM) sleep and non-REM sleep.1 Not completing the full sleep process can stress your body.

Why is sleep important?

Each sleep phase and stage is important to ensure that the mind and body are completely rested. Certain stages help you feel rested and energetic the next day, while other stages help you learn information and form memories.1,2 Sleep is important in the function of your body’s other systems, such as your metabolism and immune system. Sleep may also help your body clear toxins from your brain that build up while you were awake.1

Not getting enough or enough quality sleep contributes, in the short term, to problems with learning and processing information, and it can have a harmful effect on long-term health and well-being. According to the Centers for Disease Control and Prevention (CDC), many U.S. adults report that they don’t get the recommended number of hours of sleep each night.3

Sleep affects how well you do your daily tasks, your mood, and your health in the following ways:

  • Performance. Cutting back on sleep by as little as 1 hour can make it difficult to focus the next day and can slow your response time. Insufficient sleep can also make you more likely to take risks and make poor decisions, according to the National Heart, Lung, and Blood Institute (NHLBI).2
  • Mood. Sleep affects your mood. Insufficient sleep can make you more easily annoyed or angry, and that can lead to trouble with relationships, particularly for children and teens. Also, people who don’t get enough sleep are more likely to become depressed, according to NHLBI.2
  • Health. Sleep is important for good health.2 Research in adults has shown that lack of sleep or lack of quality sleep increases a person’s risk for high blood pressure, heart disease, and other medical conditions.2 Your environment can affect the quality of your sleep by causing disturbances that prevent you from sleeping through the night.2 Also, during sleep the body produces hormones that help the body grow and, throughout life, build muscle, fight illnesses, and repair damage to the body.2 Growth hormone, for example, is produced during sleep, and it is essential for growth and development.4 Other hormones produced during sleep affect how the body uses energy, which may explain why lack of sleep contributes to obesity and diabetes.5


  1. National Institute of Neurological Disorders and Stroke. (n.d.). Brain basics: Understanding sleep. Retrieved June 7, 2017, from https://www.ninds.nih.gov/Disorders/Patient-Caregiver-Education/Understanding-Sleep
  2. National Heart, Lung, and Blood Institute. (2011). In brief: Your guide to healthy sleep. Retrieved January 16, 2018, from https://www.nhlbi.nih.gov/resources/your-guide-healthy-sleep
  3. Centers for Disease Control and Prevention. (2016). Prevalence of healthy sleep duration among adults — United States, 2014. Morbidity and Mortality Weekly Report, 65, 137–141. Retrieved March 27, 2019, from https://www.cdc.gov/mmwr/volumes/65/wr/mm6506a1.htm
  4. Takahashi, Y., Kipnis, D. M., & Daughaday, W. H. (1968). Growth hormone secretion during sleep. Journal of Clinical Investigation, 47(9), 2079–2090.
  5. Leproult, R., & Van Cauter, E. (2010). Role of sleep and sleep loss in hormonal release and metabolism. Endocrine Development, 17, 11–21. Retrieved June 19, 2017, from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3065172/
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