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Eight hours of sleep a day seems like a colossal waste of time, doesn’t it? After all, in the hectic world we live in, those precious hours could be put to use responding to all those e-mails or hitting the spa. So why do we need so much sleep? Dr. Neil B. Kavey, director of the Sleep Disorders Center at Columbia-Presbyterian Medical Center in New York City, offers some clues:

We don't fully understand the importance of sleep. What we do know is that sleep is an anabolic, or building, process. And we think it restores the body’s energy supplies that have been depleted through the day’s activities.

Sleep is also the time when the body does most of its repair work; muscle tissue is rebuilt and restored. We know, for example, that growth hormone is secreted during sleep. This hormone is important for growth in children, but is also important throughout adulthood in rebuilding tissues.

A daily tune-up
Think of the body as a car. No car can keep going and going and going without a tune-up or oil change. If it’s not tuned, the car may keep running, but not as smoothly as it did when it was maintained properly. You can think of sleep as your body’s daily tune-up.

Human beings can function without a full tune-up, but they will be in a state of relative sleep deprivation and won’t be able to work or to think as well as they do when they are fully rested. It’s like an engine that gets only four out of eight spark plugs replaced and then runs sluggishly.

Sleep is also a time for restoring mental energy. We spend all day thinking and creating, and that uses up our energy stores.

It is interesting that in dream sleep the brain is actually very active. And this is where things get really theoretical. We’re not really sure exactly what dreams accomplish. Some experts believe that dreaming is actually some king of clearing-out process. More sleep researchers think that dreams serve the function of helping to reorganize and store psychological information taken in during the day.

Not enough ZZZ's
One of the ways we have of understanding why we need to sleep so much is to look at what happens if we don’t get enough sleep. It affects our personalities and our sense of humor. We may become irritable and less tolerant. Parents of small children often tell me that when they’re tired they get irritated at the antics of children that might amuse them if they were properly rested.

Lack of sleep clearly affects our thinking, or cognitive, processes. A sleep-deprived brain is truly running on four rather than eight cylinders. If we’re trying to be creative, the motor doesn’t work as well. We can perform calculations, but not as quickly. We’re much more likely to make errors. It’s because the brain’s engine hasn’t been replenished.

Sleep deprivation also affects us physically. Our coordination suffers. We lose our ability to do things with agility. Sleep improves muscle tone and skin appearance. With adequate sleep athletes run better, swim better and lift more weight. We also see differences in immune responses depending on how much someone sleeps.

The amount of sleep a person needs will vary from individual to individual. But most people require around eight hours.

No one really knows how humans evolved to sleep an average of eight straight hours each night. Factors that influence human sleep patterns probably include our physical size, muscle mass, brain size and the ability to think.

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