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Sleep: What is Sleep and How Much is Enough?

The average person spends about one-third of his or her life asleep. That’s a lot of time spent snoozing. So, what is sleep? Sleep is a mental and physical resting period. During sleep, muscles relax, breathing slows and blood pressure decreases.

While your body slows down and recharges, your brain enters a reduced state of consciousness; but it doesn’t shut down. In fact, neurologic studies show that the brain is very active during sleep, as the body cycles through several different phases of sleep—three stages of NREM (non-rapid eye movement) and rapid eye movement (REM). Stages 1 and 2 of NREM are light sleep; stage 3 of NREM is the deepest sleep and seems to offer the most restorative health benefits. Dreams can occur during either REM or NREM sleep, but those during the REM stage are easier to recall.

The average person alternates between NREM and REM sleep, with each phase lasting between 90 and 120 minutes. Deep-sleep cycles tend to occur in the earlier part of the night. As the night goes on, more time is spent in REM and light-sleep cycles. That’s why people are more easily awakened by noises early in the morning.

If you are a light sleeper and wake easily throughout the night, you probably spend more time in stages 1 and 2 of NREM. If you feel well rested and refreshed when you wake, you probably spend more time in stage 3 of NREM. Rather than worrying about the different stages of sleep, however, sleep medicine specialists suggest focusing on overall sleep and making sure you get enough.

How much sleep is enough? The average adult needs between 7 and 8 hours of sleep each night, but each person is different and has unique sleep needs. Children require more sleep than adults. Teens, for example, need about 9 hours, and school-age children need 10 to 11 hours to perform at their highest levels.

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