A new study out of Australia shows that children who go to sleep early and wake up early are less likely to be obese. The results, published in the Oct. 1 issue of the journal Sleep, indicate that it’s not so much the amount of sleep kids get, but the times at which they get it that has the biggest impact on their weight.
The study recorded the bedtimes and wake times of 2,200 Australian children, ages 9 to 16, and compared their weights and uses of free time over four days. Though they got virtually the same amount of sleep, children who went to bed late and got up late were 1.5 times more likely to become obese than those who went to bed early and got up early. According to the study, the difference is driven by the sedentary nature of late-night activity, as late-nighters were also nearly twice as likely to be physically inactive, and 2.9 times more likely to sit in front of the TV and computer or play video games for more hours. On average, they watched TV, played video games or were online 48 minutes longer each day than their early-bed/early riser counterparts.
Other highlights include:
- Early-bed/early-risers went to bed 70 to 90 minutes earlier, woke up 60 to 80 minutes earlier and accumulated 27 minutes more moderate to vigorous physical activity each day than late-risers.
- On a broad scale, late-bed/late-risers replaced about 30 minutes of moderate to vigorous physical activity with 30 minutes of sedentary behavior each day, relative to the early-bed/early-rise group.
- Late-bed/late-risers tended to have few siblings, live in major cities, come from lower -income households and have a part-time job.