Children who do not get enough sleep are more likely to be obese

The less children sleep the fatter they become, researchers have found. Hectic parental lifestyles and lax bedtimes for their offspring may be driving the explosion in child obesity.

A study of 422 children between five and 10 found one in five of the boys and one in four of the girls was overweight or obese.

On average the children slept for 12 to 13 hours a night. But those who slept for 10.5 to 11.5 hours had a 40 per cent increased risk of becoming overweight or obese. In those who slept for eight to 10 hours a night, the risk was increased more than threefold.

The findings are published in the International Journal of Obesity today. The researchers from Laval University in Quebec say the recognised risk factors of watching TV for long periods, physical inactivity and parental obesity applied to the children in the study. But the effect of lack of sleep was independent of these.

"These findings are important because sleep duration is a potentially modifiable risk factor that could be important to consider in the prevention and treatment of obesity,'' they say.

The researchers describe their findings as "provocative" given that the best way of keeping weight down is to increase activity. "It is somewhat paradoxical that sleeping may be associated with leanness. Although recommendations to get a better night's sleep and more exercise might seem to be at odds with each other from the perspective of energy expenditure and energy balance, these simple goals may become part of our future approach to combating obesity.''

Separate laboratory studies have shown short sleep duration is associated with lower levels of leptin and increased levels of ghrelin - a hormone that plays a key role in hunger and appetite.

Changes in the two hormones caused by lack of sleep could alter food intake and explain why individuals affected put on weight, the researchers say. The results suggest a "dose-response" relationship between lack of sleep and overweight, with children sleeping the least being at greatest risk of growing fat.

Previous studies have suggested there may be an "ideal zone" of sleep duration and that those who sleep longer or shorter suffer adverse effects on their energy balance. The researchers say: "Reduction in sleeping hours has become a hallmark of our society. If the findings prove to be reproducible and generalisable ... we could add sleep duration to the environmental factors that are prevalent in our society and that contribute to ... obesity."

The proportion of school-age children in Europe who are obese has risen almost 50 per cent since the late 1990s and will nearly double to 6.4 million by 2010. The number who are overweight is expected to grow by 1.3 million a year to 26 million across the EU in four years, more than a third of the child population, according to the International Association for the Study of Obesity.

More than a million children in Europe are thought to have high blood pressure or high cholesterol, putting them at risk of heart disease, and 1.4 million may have early stages of liver disorder, the association says, and 20,000 children are suffering "adult onset" or type-2 diabetes, not previously seen in children.