Scientists Finding Out What Losing Sleep Does to a Body

With a good night's rest increasingly losing out to the Internet, e-mail, late-night cable and other distractions of modern life, a growing body of scientific evidence suggests that too little or erratic sleep may be taking an unappreciated toll on Americans' health.

Beyond leaving people bleary-eyed, clutching a Starbucks cup and dozing off at afternoon meetings, failing to get enough sleep or sleeping at odd hours heightens the risk for a variety of major illnesses, including cancer, heart disease, diabetes and obesity, recent studies indicate.

"We're shifting to a 24-hour-a-day, seven-day-a-week society, and as a result we're increasingly not sleeping like we used to," said Najib T. Ayas of the University of British Columbia. "We're really only now starting to understand how that is affecting health, and it appears to be significant."

A large, new study, for example, provides the latest in a flurry of evidence suggesting that the nation's obesity epidemic is being driven, at least in part, by a corresponding decrease in the average number of hours that Americans are sleeping, possibly by disrupting hormones that regulate appetite. The analysis of a nationally representative sample of nearly 10,000 adults found that those between the ages of 32 and 49 who sleep less than seven hours a night are significantly more likely to be obese.

The study follows a series of others that have found similar associations with other illnesses, including several reports from the Harvard-run Nurses' Health Study that has linked insufficient or irregular sleep to increased risk for colon cancer, breast cancer, heart disease and diabetes. Other research groups scattered around the country have subsequently found clues that might explain the associations, indications that sleep disruption affects crucial hormones and proteins that play roles in these diseases.

"There has been an avalanche of studies in this area. It's moving very rapidly," said Emmanuel Mignot of Stanford University, who wrote an editorial accompanying the new obesity study in the October issue of the journal Sleep. "People are starting to believe that there is an important relationship between short sleep and all sorts of health problems."

Not everyone agrees, with some experts arguing that any link between sleep patterns and health problems appears weak at best and could easily be explained by other factors.

"There are Chicken Little people running around saying that the sky is falling because people are not sleeping enough," said Daniel F. Kripke of the University of California at San Diego. "But everyone knows that people are getting healthier. Life expectancy has been increasing, and people are healthier today than they were generations ago."

Other researchers acknowledge that much more research is needed to prove that the apparent associations are real, and to fully understand how sleep disturbances may affect health. But they argue that the case is rapidly getting stronger that sleep is an important factor in many of the biggest killers.

"We have in our society this idea that you can just get by without sleep or manipulate when you sleep without any consequences," said Lawrence Epstein, president of the American Academy of Sleep Medicine. "What we're finding is that's just not true."

While many aspects of sleep remain a mystery -- including exactly why we sleep -- the picture that appears to be emerging is that not sleeping enough or being awake in the wee hours runs counter to the body's internal clock, throwing a host of basic bodily functions out of sync.

"Lack of sleep disrupts every physiologic function in the body," said Eve Van Cauter of the University of Chicago. "We have nothing in our biology that allows us to adapt to this behavior."

The amount of necessary sleep varies from person to person, with some breezing through their days on just a few hours' slumber and others barely functioning without a full 10 hours, experts say. But most people apparently need between about seven and nine hours, with studies indicating that an increased risk for disease starts to kick in when people get less than six or seven, experts say.