These results come from data collected among 422 grade school students aged 5 to 10. The scientists measured the weight, height, and waist size of each participant. Information on the children's lifestyle and socioeconomic status was obtained through phone interviews with their parents.
Through body mass index measurement, the researchers determined that 20% of the boys and 24% of the girls were overweight. Children who slept less than 10 hours a night were 3.5 times more at risk of being overweight than those who slept 12 or more hours. No other factor analyzed in the study--parental obesity, parents' level of education, family income, time spent in front of the TV or computer, regular physical activity--had as much of an impact on obesity than time spent sleeping.
Hormone production is currently the researchers' prime hypothesis to explain the relationship between sleep and obesity. "Lack of sleep lowers the level of leptin, a hormone that stimulates metabolism and decreases hunger. In addition, short nights of sleep boost the concentration of ghrelin, a hormone that increases hunger," explains Professor Angelo Tremblay.
The progression of obesity and the decrease in the number of hours devoted to sleep, two phenomena that have become increasingly important social issues over the last few decades, could thus be more closely related than it would appear at first glance. Between 1960 and 2000, the prevalence of obesity doubled in the population while the average night of sleep lost one to two hours. During the same period, the percentage of young adults who slept less than seven hours went from 16% to 37%.
"It's ironic that part of the solution to obesity might lie in sleep, the most sedentary of all human activities. In light of this study's results, my best prescription against obesity in children would be to encourage them to move more and to make sure they get enough sleep," concludes Tremblay.
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