Beginning at age 3, the study finds, kids who get too little sleep tend to be overweight five years later.
Doctoral student Emily Snell and colleagues reached that conclusion after looking at sleep data collected from a national sample of 3- to 12-year-old children. Five years later, they took a second look at 1,441 of those children.
"We found that even an hour of sleep makes a big difference in weight status," Snell says in a news release. "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."
The National Sleep Foundation recommends that 5- to 12-year old kids get 10 to 11 hours of sleep each night. Teens should get eight to nine hours of sleep.
But Snell and colleagues found that, by their seventh birthday, kids were sleeping less than 10 hours on weekdays. This fell to 8 1/2 hours by age 14, and to eight hours by 17.
A minority got far less sleep on weekdays:
Kids who slept less were more likely to develop weight problems. Staying up too late was linked to later weight problems for 3- to 8-year-olds, and to getting up too early for 8- to 13-year-olds.
"Parents should be encouraged to put their younger children to bed early enough so they can sleep at least 10 or 11 hours a night," Snell and colleagues conclude. "For older children, however, only later wake times were associated with lower rates of overweight. This result supports findings from the growing sleep literature encouraging later school start times, particularly for adolescents," the study continues.
The report appears in the January/February issue of Child Development.
SOURCES: Snell, E. Child Development, January/February 2007; manuscript received ahead of print. News release, Northwestern University. News release, Society for Research in Child Development.
By Daniel DeNoon
Reviewed by Louise Chang, M.D