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

There are new findings that not enough sleep may cause people to gain weight. Researchers say a lack of sleep can produce hormonal changes that increase feelings of hunger.

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

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

The scientists say these hormonal changes may be a cause of obesity in Western societies. They note the combination that sleep restriction 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 the researchers say loss of sleep may increase hunger especially for high-calorie foods, so people gain weight.

Researchers from Stanford University in California and the University of Wisconsin did the study. They found that the best amount of sleep for weight control is seven-point-seven hours a night.

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

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

Researchers from Columbia University in New York did a third study. They reported the findings at a meeting of the North American Association for the Study of Obesity.

They found that people who got less than four hours of sleep a night were seventy-three percent more likely to be overweight. This was compared to people with seven to nine hours of sleep. The researchers say that for survival, the body may be designed to store more fat during times with less sleep.

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