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.
3. Is there really such a thing as beauty sleep?
There is. Being sleep-deprived can affect the overall way you look. An example of this is weight gain. If you're not getting enough sleep, there's an increase in a digestive hormone called ghrelin, which tells your body to eat. There's also a decrease in leptin, the hormone that tells your body you're full. When you have more "eat" and less "full," you tend to overeat and put on weight.
Beyond that, hydration and skin elasticity can change due to sleep deprivation. During deep sleep, your body releases growth hormone (GH), which affects almost every cell, renewing the skin and bones and bringing back organ and tissue function to more youthful levels.
For many, GH acts like a natural cosmetic, restoring skin elasticity, smoothing wrinkles, and tending to hair and nails. Conversely, lack of sleep speeds up arterial aging -- affecting the blood vessels that nourish the body and the skin -- which has a direct relationship on how your skin looks and feels. Puffiness or bags under the eyes can be caused by fluid retention, loss of skin firmness and elasticity, or fatigue, many of which are triggered by poor sleep. Dark circles under the eyes can also be due to poor blood circulation -- again, the result of lack of sleep.
4. Are sleep patterns inherited?
Absolutely. Research shows there are genetic components to not only sleep disorders but also overall sleep quality. If your mom or dad, for example, was a bad sleeper and your grandmother was a bad sleeper, you might have a high proclivity for sleeping poorly.
For sleep disorders, the cranial facial structure (meaning the skull and front of your face) is passed down from generation to generation. This may have a lot to do with your risk of developing sleep apnea, which can affect the quality and quantity of your sleep.
5. Do naps help make up for lost sleep?
They do. I'm a big proponent of naps. The only time I don't recommend people nap is if they have insomnia -- difficulty either falling asleep or maintaining sleep.
New evidence suggests that the ability to fall asleep is directly related to the last time you were asleep. You have to build up "sleep pressure" over the course of the day. So if the last time you were awake was 6 a.m., your pressure is going to be far higher at night than if the last time you woke up was 2:30 in the afternoon. Taking a nap halfway through the day reduces that pressure, and that can make it difficult to sleep at night.
The goal of a nap is to dip the body and mind briefly into stage 2 sleep, which can last for about 20 minutes, or to make it through one entire sleep cycle. Napping longer can leave you with sleep inertia -- that groggy feeling where you feel worse than before you napped. That's why I recommend 30-minute power naps or 90-minute restorative naps, both of which can leave you feeling refreshed and energized.