Sept. 30, 2011 -- Kids and teens who don’t get enough sleep are more likely to become obese and have other health problems, but new research suggests that the timing of sleep may be as important as total sleep time.
In the Australian study, older children and teenagers who went to bed latest and woke up latest were more likely to gain weight than those who went to bed earliest and got up earliest, even though total sleep times for the two groups were virtually the same.
The current thinking in sleep medicine is that adolescents tend to be biologically hardwired to have later sleep and wake times.
Although this may be the case, the new research suggests that Ben Franklin’s proverb "Early to bed and early to rise ..." may be true for teens as well as younger children and adults.
“Later sleep and waking times were associated with unfavorable activity patterns and health outcomes in our study,” researcher Carol Maher, PhD, of the University of South Australia, tells WebMD. “While teens may naturally stay up late and wake up later, the results of this study could stand as a warning that this sleep pattern might have negative consequences.”
Late Sleepers Heavier, More Sedentary
The study included 2,200 Australian children and teens between the ages of 9 and 16 enrolled in a larger health study that required them to record in detail their activities -- including sleep and wake times -- over the previous two days on two different occasions (four days total).
Because older children tend to have later sleep/wake times than younger ones, and boys tend to get up and go to sleep later than girls, the bedtimes and wake times were adjusted for age and sex.
The children were placed in one of four groups, based on their responses:
- Early bed/early risers
- Early bed/late risers
- Late bed/early risers
- Late bed/late risers
Children and teens in the late/late group and those in the early/early group each got about 9 1/2 hours of sleep over each recalled day, while the early bed/late risers got about an hour more and the late bed/early risers got about an hour less.
Those who woke and went to bed late were 1.5 times more likely to be obese than those who woke and went to bed early.
Among the other findings:
- Early bed/early risers got about half an hour more of moderate to vigorous exercise each day that those with the latest bed and wake times.
- The late/late group reported 48 additional minutes of screen time each day than the early/early group, mostly between the hours of 7 p.m. and midnight.
- Almost one in three (29%) with late bedtimes were overweight or obese, compared to closer to one in five (21%) with early bedtimes.
- Just 12% of children and teens in the late/late group had an average of two hours or less of screen time each day, compared to 28% of children in the early/early group.
Interests May Drive Sleep Timing
It isn’t clear from the study if going to bed and waking up earlier caused the children to exercise more, eat less, and generally have healthier lifestyles.
It may be that kids who are more physically active went to sleep earlier each day because they were sleepier and that they got up earlier to meet athletic schedules, Maher says.
Likewise, more sedentary children and teens may be less tired at night and those who prefer TV and video games to sports may stay up to watch favorite shows or engage in more screen time.
“Our findings are really food for thought,” she says. “We’ve tended to focus only on sleep duration. This study suggests that the timing of sleep may be just as important or even more important.”
Pediatric sleep specialist William Kohler, MD, medical director of the Florida Sleep Institute in Tampa, says the new research warrants further investigation into the importance of sleep timing.
He says that like adults, natural sleep cycles in older children and teens may be more variable than has been realized.
“While most adolescents may have a natural tendency to go to bed and wake up later, there may be a subset whose natural clock is earlier,” he says. “But this doesn’t change the message that sleep quantity as well as sleep quality are both important for good health.”