New research suggests preschoolers who are in bed by 8pm are far less likely to be obese as teenagers.

Preschool children who go to bed by eight o'clock every night have half the risk of becoming obese as a teenager, a US study has found.

Researchers at Ohio State University found bedtimes after 9pm appeared to double the likelihood of obesity later in life.

For the US study, published in The Journal of Pediatrics, researchers used data from close to 1000 children all born in 1991.

The bedtimes for the children aged four-and-a-half were divided into three categories: 8pm or earlier, between 8pm and 9pm, and after 9pm.

A link between the preschoolers' bedtimes and their weight as teens, at an average age of 15, was found.

In fact, only one in 10 of the children with the earliest bedtimes were obese teens, compared to 16 per cent of children with mid-range bedtimes.

More then 20 per cent of the children who went to bed after 9pm were found to be obese.

Factors such as socioeconomic status, maternal obesity and parenting style were taken in to account but the researchers still found that children who went to bed by 8pm were at less than half the risk of teenage obesity compared to those who were up past 9pm.

Previous research has established a relationship between a lack of sleep and obesity, but this is the first to use data on obesity collected about a decade after the children were in preschool, said lead author Professor Sarah Anderson.

Although the study does not prove that early bedtimes protects against obesity, Dr Anderson says "for parents this reinforces the importance of establishing a bedtime routine.

Putting a child to bed early doesn't guarantee the child will fall immediately into a deep sleep, however establishing a consistent bedtime routine makes it more likely that children will get the amount of sleep they need to be at their best, she said.