Full 40 winks more important than previously thought

Getting enough sleep on a daily basis is important to purge cellular waste buildup in the brain, according to a new study. And those who think they can make up lost sleep on the weekend are mistaken—the effects of sleep depravation don’t completely recede with recovery sleep.

Researchers know sleep-deprived people have slower reactions and difficulty learning and making decisions, but despite decades of research, scientists can’t agree on the basic purpose of sleep. Researchconducted at the University of Rochester Medical Centersuggests at least one purpose may be a cleaning spree for the brain.The research, performed on sleeping mice, may provide new clues to treatment for Alzheimer’s and a range of other brain diseases.

The researchers previously found a plumbing network in mouse brains that flushes out cellular waste. For the new study, scientists injected the brains of mice with a substance that builds up in Alzheimer's disease, and then followed its movement. They determined it was removed faster from the brains of sleeping mice than from awake mice. The team also noticed that brain cells tended to shrink during sleep, widening the space between cells and allowing waste to pass through more easily.

According to Clete Kushida, a doctor with the Stanford Sleep Medicine Center, the finding may mean that sleep is important in slowing the progression of damage for people with dementia and other brain disorders.

Not only might lack of sleep prevent the brain from doing housecleaning, but even a few days of lost sleep can have adverse effects, including increased daytime sleepiness, decreased performance, increased inflammation, and impaired blood sugar regulation, according to another sleep study reported in Science Daily. Researchers led by Alexandros N. Vgontzas, of Penn State University College of Medicine, studied what happens when people who are sleep-deprived during the workweek try to catch up on the weekend.

The researchers placed 30 volunteers on a sleep schedule that mimicked a sleep-restricted workweek followed by a weekend with extra recovery sleep. At various points, researchers assessed the volunteers’ health and performance. Many indicators of health and well-being improved after recovery sleep and levels of a hormone that is elevated with stress were significantly lower. But, measures that assessed ability to pay attention deteriorated significantly with sleep deprivation and did not improve after recovery sleep, implying that sleep over just a single weekend does not appear to reverse impairment of attention due to sleep restriction during the workweek.

These results may be especially important for people with jobs for which safety issues are critical. The authors suggest that even though these results provide some insight on the health effects of a single week of sleep loss followed by two days of recovery sleep, reliving the cycle over and over again may have more significant health effects.

The Associated Press contributed to this article.