I'm Gwen Outen with the VOA Special English Health Report.

There are new findings that not enough sleep may cause people togain weight. Researchers say a lack of sleep can produce hormonalchanges that increase feelings of hunger.

In one study, researchers in the United States examinedinformation on more than one thousand people. The people had takenpart in a long-term study of sleep disorders.

Some people slept less than five hours a night. They had fifteenpercent higher blood levels of a hormone called ghrelin than peoplewho slept eight hours. And they had fifteen percent less of thehormone leptin. Experts say ghrelin helps make people feel hungry;leptin makes you feel full.

The scientists say these hormonal changes may be a cause ofobesity in Western societies. They note the combination that sleeprestriction is common and food is widely available.

The results were not affected by how much people exercised.People who are awake longer have more time to burn energy. But theresearchers say loss of sleep may increase hunger especially forhigh-calorie foods, so people gain weight.

Researchers from Stanford University in California and theUniversity of Wisconsin did the study. They found that the bestamount of sleep for weight control is seven-point-seven hours anight.

The Public Library of Science published the findings in itsjournal Medicine. Internet users can read the full study, free ofcharge, at plos.org.

Researchers at the University of Chicago did a smaller study,reported in the Annals of Internal Medicine. They found that peoplewho slept just four hours a night for two nights had an eighteenpercent reduction in leptin. And they had a twenty-eight percentincrease in ghrelin. The young men in that study also appeared towant more sweet and starchy foods.

Researchers from Columbia University in New York did a thirdstudy. They reported the findings at a meeting of the North AmericanAssociation for the Study of Obesity.

They found that people who got less than four hours of sleep anight were seventy-three percent more likely to be overweight. Thiswas compared to people with seven to nine hours of sleep. Theresearchers say that for survival, the body may be designed to storemore fat during times with less sleep.

This VOA Special English Health Report was written by CynthiaKirk. I'm Gwen Outen.