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- Learn what happens during sleep and why it’s crucial to good health
- Evaluate your sleep habits and improve the quality of your night’s sleep
- Overcome the most common sleep problems, from insomnia to snoring
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The Facts About Sleep
Despite the fact that we all experience it every night, sleep remains a mystery to many of us. Understanding the physical and mental complexities of sleep is the first step to recognizing its importance to your health.
What Happens During Sleep
While your body rests, your brain remains active and experiences several stages of sleep in two different states:
- REM sleep: REM (rapid eye movement) sleep is the most active kind of sleep, in which dreams occur.
- Non-REM sleep: The more frequent non-REM sleep accounts for roughly 75% of a night’s slumber.
In a typical eight-hour period of sleep, you alternate
between these two states roughly every 90 minutes. One 90-minute cycle of sleep consists of five stages—four non-REM stages and one REM stage.
- Stage 1: This stage is the transition between being awake and sleeping, when some parts of the brain are asleep and others aren’t. Thoughts drift, but you’re still easily awakened.
- Stage 2: This stage marks the onset of sleep, when breathing and heart rate become regular and the body temperature lowers.
- Stages 3 and 4: These stages, also called delta sleep, are deep periods of sleep in which muscles relax, blood pressure drops, and breathing slows. Stages 3 and 4 are the most physically restorative periods of sleep, when growth hormones are released for tissue repair in muscles and bones.
- Stage 5: REM sleep occurs during the fifth stage. Muscles shut down and become nearly paralyzed, but the brain is intensely active. During this stage, the eyes dart rapidly back and forth under the eyelids, and vivid dreams occur. Breathing and heart rate increase and may become irregular. Stage 5 sleep is necessary for providing your brain and body with energy and is suspected to play an important role in mental recovery.
Why Sleep Is Important to Health
Quality sleep occurs when you experience these five stages in continuous succession, 4–6 times a night. When this happens, you awake feeling revitalized and refreshed. Physical and mental benefits of good sleep include the following:
- Muscle and bone repair
- A healthier immune system
- Appetite control (via regulation of two hormones, ghrelin and leptin)
- Memory consolidation
- Daytime alertness
When you lose sleep, both your health and your quality of life suffer. The potentially harmful effects of not getting enough sleep—even for just a night or two—include:
- Excessive daytime sleepiness (EDS)
- Decreased daytime alertness
- Increased risk of motor vehicle or on-the-job accidents
- Impaired immune system
Chronic sleep loss can have even more serious, long-term effects, including:
- Decreased ability to remember new information
- Irritability and erratic behavior
- Impaired ability to use insulin, increasing the long-term risk for diabetes
- Increased long-term risk of heart problems, stroke, high blood pressure, and cancer
- Increased risk of psychiatric problems, including depression and substance abuse
- Weight gain and increased risk of obesity, due to increased appetite and slowed metabolism
It is possible that regularly getting too much sleep—known as long sleep—may also have its dangers. Though research is not yet conclusive, studies have indicated that there may be a link between health problems and increased mortality in adults who regularly sleep nine or more hours per night.
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