In each issue of WebMD the Magazine, we put five of the most-asked questions on the WebMD community boards to one of our health experts. In our January-February 2011 issue, we gave WebMD's sleep expert, Michael Breus, PhD, ABSM, the top five sleep questions -- including why we need it, how much we need, even whether or not it can really make us beautiful.
1. Why do we sleep?
Great question. Unfortunately, we don't have a great answer. We're still kind of baffled about why we sleep. We know that we need it -- and that there's an internal drive for it, like hunger, that we can satiate. But it's very difficult to put a finger on the exact purpose of sleep.
What we do know is that several critical things happen during sleep. Every 80 to 120 minutes we progress through five stages of sleep -- drifting off in stage 1, light sleep in stage 2, deeper sleep in stages 3 and 4, and REM or rapid eye movement sleep in stage 5. Stages 3 and 4 are the most physically restorative; your body emits growth hormones and refreshes itself by repairing any muscular damage done during the day. In stage 5 or REM sleep, your mind restores itself: The brain moves information from your short- to your long-term memory and makes specific connections to organize thoughts so you can recall them later.
2. Do we need less sleep as we age?
This is really more a myth than a fact. A lot of folks age 65 and older say they require less sleep, but that's not the case. They still need roughly the same amount of sleep -- somewhere between 6.5 and 8.5 hours -- but because they may not be as active as they once were or they have opportunities to take unscheduled naps throughout the day, they get those hours someplace else. They just end up with less sleep at nighttime.
Eight hours of sleep a night is also a myth. The average American is sleeping between 6.8 and 6.9 hours. And that might be fine. It all depends on the individual and the quality of sleep, not just the quantity.
Children are another story; their sleep needs are dramatically different from those of adults. What we know is that people's sleep needs do change over time or with their health. There's even data to show that people who sleep more than 10 hours or less than 5 hours in each 24-hour period have double the mortality rate.