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

Many people report that they experience problems with sleep. But what does that really mean?

Sleep problems differ in how severe they are and in their specific features.¹ For example, how long you sleep or are awake, how deeply you sleep, and how you fall asleep are all related to certain sleep problems.

In the past, healthcare providers focused on sleep deprivation—not getting enough sleep (also called insufficient sleep)—as a main type of sleep problem. But research has shown that sleep deficiency, a concept that describes a group of sleep problems, is actually a more accurate way to talk about sleep problems.

Sleep deficiency is a term that describes several different sleep issues, including:

• Not getting enough sleep (sleep deprivation or insufficient sleep)
• Sleeping at the wrong time of day (not in sync with your body’s natural clock)
• Not sleeping well or not spending enough time in certain stages of sleep
• Having a sleep disorder

Sleep deficiency is associated with a number of health and other problems ranging from feeling tired to chronic health conditions. Visit https://www.nhlbi.nih.gov/health-topics/sleep-deprivation-and-deficiency for more information.

Sleep disorders are a group of more than 70 major sleep problems with symptoms that can include inappropriate sleep, severe sleep deprivation, and periods of stopped breathing. People with sleep disorders usually benefit from treatments and monitoring from a healthcare provider. The National Heart, Lung, and Blood Institute (NHLBI)—which leads sleep disorder research at NIH—offers in-depth information about many sleep disorders, including:

• Insomnia
• Sleep Apnea
• Narcolepsy

Visit https://www.nhlbi.nih.gov/health-topics to search for all sleep-related topics on the NHLBI website.

Sleep and wakefulness are generally regulated by our brains working with input from our senses and our circadian (pronounced sur-KAY-dee-uhn) clock.

This system pushes us to wake up and remain awake at certain times and pushes us to sleep at certain times. Research has helped us to begin to understand this system at the level of the cells in the brain. More work is needed to understand exactly how the brain, senses, and our body’s clock work in waking and sleeping and what can happen to disturb this cycle. Visit the National Institute of Neurological Disorders and Stroke’s Understanding Sleep page for more information on the sleep cycle.

In broad terms, the brain of someone who is sleeping cycles through two basic phases: rapid eye movement (REM) sleep and non-REM sleep. Non-REM sleep includes three different stages.¹ A person cycles through REM sleep and non-REM sleep several times a night.

For more detailed information about what happens during sleep and phases of sleep, check out Your Guide to Healthy Sleep, from the National, Heart, Lung, and Blood Institute.

Each phase of sleep helps the mind and body stay rested. Certain stages help you feel rested and energetic the next day, while both phases help you learn information and form memories.^1,2

Sleep progresses in a cycle: from non-REM sleep stage 1 to non-REM sleep stage 2, to non-REM sleep stage 3, to REM sleep. Then the process starts over again with non-REM sleep stage 1.

The length of sleep stages changes during a given night’s sleep. For example, near the beginning of sleep, the body cycles through relatively short periods of REM sleep and long periods of deep sleep. As the night goes on, periods of REM sleep increase and those of deep sleep decrease. Near the end of a night of sleep, a person spends nearly all of their time in stages 1 and 2 and REM.³

Some of the characteristics of each phase include the following.

According to the National Institute of Neurological Disorders and Stroke, the amount of sleep people need depends on several factors, including their age, individual requirements, and whether they have been getting adequate sleep.¹

The National Sleep Foundation recommends how much sleep people should get at each age. The recommendations are based on a review of more than 300 research studies.²

Although the amount of sleep you get each day is important, other aspects of your sleep also contribute to your health and well-being. Good sleep quality is also essential. Signs of poor sleep quality include not feeling rested even after getting enough sleep, repeatedly waking up during the night, and experiencing symptoms of sleep disorders (such as snoring or gasping for air). Improving sleep quality may be helped by better sleep habits or being diagnosed and treated for any sleep disorder you may have.

There are several common myths about sleep, including the following¹:

Medical conditions, including pregnancy, some intellectual and developmental disabilities (IDDs), depression, Alzheimer’s disease, and cancer, may disrupt natural or healthy sleep patterns.

• Pregnancy. Many women who become pregnant find that they develop sleeping problems during pregnancy that they did not have before they got pregnant. Fatigue is common during pregnancy, especially during the first and third trimesters.^1,2 Pregnant women may develop problems such as insomnia, restless legs syndrome, sleep apnea, nighttime heartburn―which can cause long-term damage to the esophagus―and frequent nighttime urination. All of these problems can affect the quality of sleep as well as sleep duration. Visit the March of Dimes website for suggestions on improving sleep during pregnancy: http://www.marchofdimes.com/pregnancy/yourbody_sleeping.html .
• IDDs. IDDs, particularly among children, are associated with sleeping problems. For example, children with autism spectrum disorders or attention deficit/hyperactivity disorder often have sleep problems.^3,4 The specific treatment or intervention depends on the IDD, the child’s age, and other factors.
• Other conditions. Sleeping problems are common in people with intellectual disabilities or mental health problems, such as depression or schizophrenia.⁵ Sleeping difficulties are also common in many other disorders and illnesses, including Alzheimer’s disease, stroke, cancer, and head injury.⁶ Some researchers believe that many of these sleep problems happen because of changes in the brain areas that control sleep and waking. Medicines used to control the symptoms of certain conditions (cancer, for example) can also cause sleep problems.⁶

Inadequate sleep—such as not sleeping long enough overall or having poor quality sleep—affects both how we feel and how we function.

Short-term effects can include drowsiness or sleepiness, irritability, reduced alertness, poor motor skills, and attention problems.

Inadequate sleep over a longer period of time can affect how the body functions. For example:

• NIH research shows that not getting enough sleep is associated with excess body weight and obesity.¹ All age groups, including children, seem to be affected in the same way.² In addition, blood samples from people who get little sleep show metabolic changes that are similar to those seen in obese people.³
• Sleep duration is associated with type 2 diabetes. A review of 10 studies involving more than 18,000 people found that people who got between 7 and 8 hours of sleep per day have the lowest risk of diabetes. Those who sleep more or less than that 7 to 8 hours have a higher risk of having diabetes.⁴
• Sleep apnea, a condition in which a person temporarily stops breathing while sleeping, increases risk for several different cardiovascular conditions, including high blood pressure (hypertension), stroke, coronary heart disease, and irregular heartbeat.⁵
• Research has also found that inadequate sleep increases blood pressure levels in people who already have hypertension. This finding may be one reason why people who lack sleep over time have an increased risk of cardiovascular disease.⁶
• Inadequate sleep, especially over a long period of time, can lead or contribute to mood disorders. Chronic sleep problems have been linked to depression, anxiety, and mental distress. For example, one study reported that participants who slept only 4.5 hours per night were more stressed, sad, angry, and mentally exhausted than a comparison group with longer sleep.⁷ In extreme cases, sleep deprivation is also linked to psychosis, paranoia, and hallucinations. Disrupted sleep can also trigger manic episodes, including agitation and hyperactivity, in people with bipolar disorder,⁸ a mood disorder in which people may cycle between extreme highs and extreme lows in their mood.
• Sleep disturbance has been linked to pain and disability. For example, in a recent NIH-supported study of arthritis patients, sleep disturbance was associated with pain and depression and predicted disability.⁹ In another study of arthritis patients with knee or hip replacement, researchers found that pain was associated with disturbed sleep but also that disturbed sleep was linked specifically to pain symptoms.¹⁰

Natural products, including over-the-counter sleep aids, dietary supplements, and herbal products, are called “natural” because they may contain a substance that is found naturally in the environment. However, it’s important to note that many natural products don’t go through the same safety and approval process as prescription or over-the-counter medicines. It’s important, then, to discuss these products with a healthcare provider before taking them to make sure that they won’t interact with other things you are taking and to avoid any unintended or dangerous side effects.

According to the National Center for Complementary and Integrative Health (NCCIH), only some natural products have been studied as sleep aids. For example, very little research has been done on kava’s usefulness in alleviating sleep problems, but the research that has been done links kava to serious health problems, including severe liver damage. Studies on chamomile and valerian have not shown conclusively that these herbs help treat sleep disorders.¹

Find more information about alternative therapies for sleep disorders on the NCCIH website. Remember to speak with your healthcare provider before taking any medication, including natural products and supplements.