How Long Is a Sleep Cycle?

Given the amount of time people spend asleep, this topic has historically received relatively little scientific attention. Aristotle was one of the first scholars to surmise that sleep is a time of physical renewal, but most of what is now known about sleep has been discovered in the past 100 years. Many of these breakthroughs came following the development of technologies that can measure brain activity during various stages of sleep. The different stages of a sleep cycle were first described in 1937 and the existence of Rapid Eye Movement or REM sleep was discovered in the 1950s. The study of sleep disorders gained precedence when sleep apnea was studied in the 1960s. The important connection between sleep and health emerged in the late 1990s. At about the same time, researchers uncovered a gene linked to a sleep disorder called narcolepsy. Today specialists treat patients with sleep problems at centers throughout the country.

A sleep cycle usually includes 2 very different types of sleep: Non-Rapid Eye Movement or Non-REM sleep and Rapid Eye Movement or REM sleep. Non-REM sleep is made up of 3 stages in which a person's brain waves progressively slow down over the course of an hour or so as their sleep deepens. Then a dramatic change occurs as people enter REM sleep, which is characterized not only by rapid eye movements but also rapid brain waves. Dreams occur primarily during the REM portion of the sleep cycle. People spend more time in REM sleep and less time in the third Non-REM deep-sleep stage as the night wears on.

Regular sleep is essential for survival. In fact, experts say people can live longer without food than they can without sleep. Sleep is important in terms of allowing the body to rest and recuperate. Scientists have learned that sleep also facilitates the processing of memories.

Humans are programmed to sleep at night--thanks largely to our internal clock, or circadian rhythms, which are controlled by a tiny portion of the brain called the suprachiasmatic nuclei. The circadian rhythms operate in tandem with adenosine, an inhibitory neurotransmitter that builds up during the day until the point where people feel sleepy. Sleep experts say adults generally need 7 or 8 hours of sleep each night, with children requiring even more.

To assess the benefits of sleep, consider the consequences associated with a lack of sleep. Researchers have found that a continual lack of sleep can more than double the risk of death from heart disease. Besides making people feel tired and irritable, a lack of sleep causes their performance to suffer. Each year fatigued drivers cause an estimated 100,000 motor vehicle accidents that result in 1,500 deaths.

The National Sleep Foundation offers the following sleep-improvement tips: Go to bed and get up at the same times each day. Exercise, but try to schedule workouts at least 5 or 6 hours before bedtime. Avoid caffeine, nicotine and alcohol. Relax before bed. If possible, sleep until the sun rises. Don't lie in bed awake. Keep sleeping areas dark and quiet with a comfortable temperature. See a specialist if a sleeping problem persists.