“Previous research has shown that longer sleep duration is tied to lower adiposity and weight status in youth,” explains Paul J. Collings, PhD. “Parameters such as bedtimes and sleep quality may also influence health, but they have seldom been studied. We saw an opportunity to analyze sleep-adiposity associations across a large and heterogeneous international dataset of children and adolescents.”

For a paper published in Pediatric Obesity, Dr. Collings and colleagues examined the relationship of bedtimes and sleep durations with adiposity and weight status in 12,247 children and 3,563 adolescents from 11 international studies spanning seven countries.

Longer Sleep Durations Are Linked With Lower Adiposity & Weight Status

“We examined the cross-sectional and prospective relationships of bedtimes and sleep durations with measured adiposity and weight status; sleep data were self-reported by children and their parents,” Dr. Collings says. “We also attempted to disentangle the possible associations of longer sleep durations with lower adiposity, from that of earlier bedtimes with lower adiposity, by quantifying the effects of four combinations of behaviors: later-shorter, earlier-shorter, later-longer, and earlier-longer. We anticipated that a later-shorter pattern of sleep would be least desirable, and that as sleep durations increased across categories, so would associations with lower adiposity. Any results that deviated from this pattern could highlight the importance of earlier bedtimes over longer sleep duration.”

 Longer sleep durations were found to be consistently linked with lower adiposity and weight status, replicating data from earlier research. “In addition, we discovered that earlier bedtimes were dose-dependently associated with lower BMI z-score and with lower likelihood of overweight and obesity,” Dr. Collings adds. “Compared to bedtimes later than 10:00 pm, those between 9:00 pm and 10:00 pm and before 9:00 pm were linked with 23% and 32% lower odds of overweight and obesity, respectively. Combined bedtime and sleep length groups that were defined by longer sleep were associated with lower adiposity in children. Conversely, earlier-shorter, and earlier-longer sleeping patterns appeared optimal for adolescents.”

Late Night TV Viewing Linked With Excess Snacking, Poor Sleep Quality

Compared with a baseline sleep duration of less than 10 hours, sleeping between 10 and 11 hours per night in girls and for 11 or more hours per night in boys favorably predicted changes in waist circumference z-scores, Dr. Collings notes. “In addition, an earlier bedtime between 9:00 pm and 10:00 pm favorably predicted future changes in BMI and waist circumference z-scores,” he says. “These are potentially important observations, particularly since centrally stored adiposity is more metabolically harmful than total adiposity, and because many children transition to a later sleep time as they get older. Our results back up previous evidence showing that earlier childhood bedtimes predict lower central adiposity and weight status throughout youth (Table).”

 Dr. Collings highlights that longer sleep durations and earlier bedtimes may be modifiable causes of adiposity in youth, and should therefore be targeted for obesity prevention, he says “Longer sleep for children and earlier bedtimes for adolescents may be most beneficial”. He adds that, “TV viewing seemed to partly explain why we found that poorer sleeping behaviors were linked with higher adiposity in children. Watching TV in the evening is associated with increased snacking of calorie-dense foods and with reduced sleep quality. Having a TV in a child’s bedroom is inadvisable and screen time should be limited in children with poorer sleeping habits.”

 The study team indicated the need for future research that simultaneously investigates multiple sleep dimensions to better understand their independent and collective relations with health. “Studies should also strive to investigate ethnic minority and socioeconomically disadvantaged populations,” Dr. Collings adds. “It is important to determine the extent to which shifted sleep schedules may explain why childhood obesity rates are higher in ethnic minorities and disadvantaged populations.”