LOS
ANGELES, Feb. 7 (Xinhua) -- Children who sleep less have a greater risk of being
overweight, according to a new study.
In two waves of data collection approximately five
years apart, researchers at the U.S. Northwestern University examined 2,182
children, using time diaries to record all activities -- including bedtime, time
asleep and wake time -- over the course of a weekday and weekend day.
"Our study suggests that earlier bedtimes, later wake
times and later school start times could be an important and relatively low-cost
strategy to help reduce childhood weight problems," said Emily Snell, co-author
of the study, which was published in the January/February issue of Child
Development.
In analyzing the diaries, the researchers found
troubling age-related trends in sleep behavior.
By age seven, children were sleeping on average less
than 10 hours on weekdays. By age 14, weekday sleep time fell to 8.5 hours. A
full 16 percent of adolescents aged 13 to 18 were found to sleep fewer than
seven hours on weekday nights. The National Sleep Foundation recommends children
aged 5 to 12 years get 10 to 11 hours of sleep and adolescents get eight to nine
hours.
Their findings suggested that later bedtimes play a
greater role in the overweight status of children aged from 3 to 8, while
earlier wake times play a greater role in children aged 8 to 13. No significant
differences in the effect of sleep on weight was found between boys and girls
nor was there evidence that children who slept more grew more in height.
The study is the first nationally representative,
longitudinal investigation of the relationship between sleep, Body Mass Index
(BMI) and overweight status in children aged 3 to 18.
"We found even an hour of sleep makes a big
difference in weight status," said Snell, a Northwestern doctoral student in
human development and social policy.
"Sleeping an additional hour reduced young children's
chance of being overweight from 36 percent to 30 percent, while it reduced older
children's risk from 34 percent to 30 percent," said Snell.
The study not only differs from most other
investigations of the effects of sleep on children's weight in its five-year
approach. It also helps disentangle the issue of whether sleep actually affects
weight or whether children who already are overweight are simply poor sleepers.
In addition, it takes into account the possible effects of other variables
including race, ethnicity and income.
"Many American children are simply not getting the
sleep they need. Parents, policymakers and health care providers all are
concerned about the obesity epidemic among children," said Snell. " Our results
suggest that something as simple as helping children sleep more at night could
reduce their risk of being overweight."
