Early bedtime for kids helps beat flab

Children who stay up late may be packing on extra kilos because they get hungry and head to the kitchen on the way to bed.

An Auckland study found that children who slept for less than 9.5 hours on week nights were twice as likely to be obese as those who slept at least 11 hours.

Five-year-olds need 11 to 12 hours sleep and 11-year-olds nine to 10 hours.

"Although there may be physiological mechanisms involved, it is also likely that children who are awake later at night will snack before bed," said Auckland University of Technology researcher Scott Duncan, who ran the study.

"Putting food into your body as soon as you go to bed, you are not burning that off as energy. You are more likely to be storing that as fat."

Fight the Obesity Epidemic spokeswoman Dr Robyn Toomath, a diabetes specialist, said the link may be that the late bed-goers were watching television, "not that they are staying up late or hanging around the kitchen.

"TV is full of ads to eat food and we know that when you watch all those ads you eat food and studies show you eat the food that's being advertised."

Mr Duncan, a doctoral student, put step-counting meters on more than 1200 primary school pupils across Auckland, measured their body fat and asked parents about the 5 to 11-year-olds' eating and activity habits.

He found boys on average took 16,420 steps each week day, about 2000 more than girls. They both moved less at weekends, boys dropping to 13,050 and girls to 11,520.

Schools now kept children active with sports and exercise programmes, but some parents put little emphasis on physical activity, leading to a weekend slow-down, he said.

Maria Heron, the principal of one of the schools in the study, Mangere Central, said she was not surprised to find that boys moved more than girls.

"Boys run around and go further on the field ... Girls will tend to visit the library or sit in groups and talk."

Rongo O'Connor said two of her grandchildren at the school, cousins James, 11, and Jordan, 8, were both active children. But Jordan was less active and was overweight.

"He never stops eating and drinking. I was trying to get him just to drink water instead of Refresh from the fridge. He is starting to drink water. JR [James] drinks plenty of water or milk."

Both boys go to bed at 8.30 to 9pm and wake around 7.30am. Jordan plays sport at school and is not obese, Ms O'Connor said.

"I hope he doesn't get to that stage. I don't think he will - not if I have my way he won't. I'll probably have to get him into some weekend sport."