Not getting enough sleep doesn't just make kids cranky — it's setting them up for obesity, a new study suggests.

Five-year-olds who slept less than 11 hours a night were more eager to eat at the sight or reminder of a favorite snack, compared to those who slept longer, researchers reported in the International Journal of Obesity.

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The new study involved over 1,000 5-year-olds born in 2007 in England and Wales, who slept an average of 11.48 hours at night.

Among kids who slept less than 11 hours a night, food responsiveness was 2.53 on a scale of 1 to 5, compared to 2.36 for those who slept 11 to 12 hours, and 2.35 for those who got at least 12 hours of sleep a night.

The children who slept less than 11 hours at night also had a higher body mass index than those who slept 11 hours or more. The Centers for Disease Control and Prevention recommends between 11 and 12 hours of sleep for children younger than 6 years old. 

Eating out of pleasure, not hunger

“There is now accumulating evidence in both children and adults to suggest that short or insufficient sleep increases reward-driven eating,” says Laura Mcdonald , the study’s lead author and a researcher at University College London.

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“This is, of course, a concern,” she adds, “given that we live in a modern ‘obesogenic’ environment” where tasty, high-calorie foods “are widely available and cheap to consume.”

Previous studies have shown that too little sleep significantly increases the chances that a child will be overweight or obese. But less was known about how sleep affects daily calorie intake.

“Some studies using brain imaging in adults have shown that sleep restriction increases responsiveness in reward centers of the brain in response to images of palatable food,” notes Mcdonald.

Cause or effect?

While the study doesn’t prove that less sleep causes more eating, Mcdonald suggests that the relationship between the two may be even more complicated.

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“It is definitely a possibility that food responsiveness might impact sleep behavior,” she says. “For example, it could be that children who are more food responsive are also more difficult to settle at night.”