Children who get less than 11 hours' sleep a night during their primary school years are more likely to become obese adults, according to new research.
The Multidisciplinary Health and Development Study, based in Dunedin, followed more than 1000 people born in the city in the early 1970s.
The study's deputy director, Associate Professor Bob Hancox, says the findings show that 11 hours of sleep a night is about right for most primary school age children.
He says it is not clear why sleep deprivation might lead to weight gain, but it could be that it disrupts the hormones that regulate appetite.
Another suggestion is that tired children may be less active, or seek out sugary foods to boost energy levels.