We spend a quarter of our lives asleep. Although scientists realize that sleep deprivation is harmful, they grapple with why humans need to snooze. Sleep is necessary for the body to rest, yet our brains continue to process information. Some studies have shown that students are more successful when they sleep after studying -- instead of pulling all-nighters -- because the brain reviews and reinforces information learned. Similarly, dreaming is an opportunity to work out emotional problems and solidify thoughts and memories. About 25 percent of the time spent sleeping, particularly during the first 90 minutes after falling asleep, is spent in rapid eye movement, or REM, sleep [source: What Happens When You Sleep]. This type of sleep is known for when dreams occur, but it also helps energize the brain and body. REM sleep helps hormone levels adjust to promote morning alertness and regulate feelings of hunger and fullness.
According to the National Sleep Foundation, researchers have found two important factors regarding humans and sleep: basal sleep need and sleep debt. Basal sleep need is the amount of slumber we need to have regularly to perform at our best. Sleep debt is the cumulative loss of sleep. A few studies say that most adults function best with a basal sleep need of seven to eight hours a night. The problem is that sleep debt also factors in. Just because you meet your basal sleep needs a few nights of the week doesn't mean it negates the effects of one night's sleep debt.
Of course, everyone is different and some people require more or less sleep than the standard basal sleep need. But the real rub lies in what lack of sleep does over the long haul to people person who either is not in tune with his or her body's needs or for one reason or another doesn't get enough regular sleep duration for a period of time. These people are more prone to having motor vehicle accidents, weight gain and risk for heart disease or diabetes and may be at increased risk for psychiatric conditions such as depression or substance abuse. Sleeping too long also can be associated with depression and poor health [source: National Sleep Foundation].
About 40 million people in the U.S. have one of 70 sleep disorders and 60 percent of adults report that they have trouble sleeping at least a few nights a week [source: American Psychological Association].
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