New Zealand researchers found that young children who slept less than the average 11 hours a night were far more likely to have a higher body mass index by the age of seven. Each extra hour of sleep at night for children aged 3 to 5 was linked to a 61 per cent fall in the risk of being overweight or obese. The reserchers monitored nearly 250 children, regularly tracking weight, diet, body composition, physical activity and sleep patterns from the ages of three to seven.

Lifestyle and other risk factors which affected a child's weight, such as birth weight, parent's education, income and ethnicity, were all taken into account. Researcher Prof Barry Taylor, of Otago University, said reduced sleep might increase dietary intake and might also influence energy expenditure, leading to reduce exercise. The amount of sleep a person had, altered the hormones controlling metabolism and appetite, i.e. how much was eaten, Professor Taylor said "Studies have linked poor sleep to heavier children, but this was the first time such a thorough assessment had been done". Prof Taylor recommended that appropriate sleep habits be encouraged in all children, but said more research was needed.

In an editorial accompanying the Brittish Medical Journal study, Prof Francesco Cappuccio, of Warwick University in England, said, "Not only might prolonged lack of sleep be a direct contributor to obesity in children, it could also have other effects on long-term health. He called for research to explore methods to improve children's and adults sleeping time.

"In the meantime, it will do no harm to advise the general public of all ages that a sustained curtailment of sleeping time might contribute to long-term ill-health in both adults and children."