Researchers Believe They Know Why We Sleep

Joe Weinlick
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A good night's sleep is one of those luxuries everybody imagines getting—someday. American adults now average 6.9 hours of sleep a night, instead of the average eight hours that are recommended for most people. Sleep problems aren't a joke. Every year, thousands of healthcare workers make thousands of avoidable errors due to lack of sleep. Identifying the causes of sleep deprivation, and learning to treat them, are clearly important to building a safer, more effective therapeutic environment. But first, what is sleep, anyway, and why do researchers think they've found the reason we need it?

Sleep is that (ideally) eight hours every night when your body and mind shut down, you begin to dream about whatever weird thing is on your mind, and wake up feeling refreshed and ready to face the day. Strangely, for something that occupies a third of the human lifespan, scientists have had trouble figuring out what it's for.

It used to be thought that the human body needed a long period of inactivity to repair the damage to muscles and bones that the day's rigors had inflicted, but sleep studies from the 1950s showed that most people are physically active several times a night. Certainly, there's no physical benefit from sleep that couldn't be had by simply lying very still for several hours while keeping alert for the predators that must have stalked early humans.

The next big step forward came when healthcare professionals, working on the issue of sleep problems in adults, discovered the massive changes in brain activity that coincide with dreaming. Indeed, test subjects who have been awakened during the night at the exact moment they began to dream usually wake up feeling no better than when they went to bed. Clearly, sleep is for dreaming and other brain-related activities. This is reinforced by the observation that many organisms with simple nervous systems skip sleep altogether.

Now, an American team of researchers, seeking to unlock the key to sleep problems, thinks it has the answer: housekeeping. The team, led by Maiken Nedergaard, of the University of Rochester, suggests that sleep is a time when your brain cells actually shrink, allowing cerebrospinal fluid to circulate more freely throughout your brain, clearing away molecular waste products that have built up during the day. In this model, sleep lets your brain flush itself clean, while sleep problems would result in a buildup of these waste products, causing impaired function during the waking hours.

Sleep problems affect everybody from time to time, but chronic sleep problems tend to turn into work problems that increase the risk for patients and coworkers alike. The causes of sleep deprivation are only imperfectly understood so far, but the effects of sleep problems on the healthcare industry are unmistakable.


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