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A team led by Prof. Song Chan-hi of the Family Medicine Division at St. Mary's Hospital in Seoul conducted a survey of 362 women to see if there was a correlation between the amount of sleep and obesity. Participants were divided into three groups: those who slept less than seven hours, those who slept seven to 7.9 hours, and those who slept eight hours or more. The middle group showed the lowest rate of obesity.

In other words, if this group's obesity rate was set at 1, the obesity rate of the group with less than seven hours of sleep became 2.2, and that of the group sleeping the longest 2.21.

Previous research has revealed that lack of sleep can contribute to obesity because sleep deprivation decreases leptin, an appetite-suppressing hormone, increases the appetite-stimulating ghrelin, and reduces insulin resistance.

In Song's study, the group with the least sleep had a higher obesity rate despite a lower calorie intake. The group sleeping eight hours or more took in plenty of calories and also had more obese members in their family than other groups.

"The obesity of those sleeping eight hours or more seems to be related to their eating habits and amount of exercise, but the obesity of those sleeping less than seven hours appears to be more related to hormones," Song said.

(englishnews@chosun.com )