Does a later sleep schedule relate to activity and weight, even with similar sleep duration?

Details

The study aimed to assess how early and late bedtimes and wake times relate to use of time and weight status in Australian school-aged children. It was an observational cross-sectional study using time-use interviews and pedometers. Participants were free-living Australian adolescents: 2,200 9- to 16-year-olds from all states of Australia, with no intervention.

Bedtimes and wake times were adjusted for age and sex, then classified as early or late using median splits. Adolescents were placed into four groups: early-bed/early-rise, early-bed/late-rise, late-bed/early-rise and late-bed/late-rise. The groups were compared on use of time, including screen time, physical activity and study-related time, as well as sociodemographic characteristics and weight status.

Despite similar sleep durations, the late-bed/late-rise group had 48 minutes per day more screen time and 27 minutes less moderate-to-vigorous physical activity (MVPA) than the early-bed/early-rise group (P<0.0001). The late-bed/late-rise group also had a higher BMI z-score (0.66 vs. 0.45, P=0.0015). Compared with the early-bed/early-rise group, they were 1.47 times more likely to be overweight or obese, 2.16 times more likely to be obese, 1.77 times more likely to have low MVPA and 2.92 times more likely to have high screen time. They were also more likely to come from poorer households, live in major cities and have fewer siblings.

The researchers concluded that late bedtimes and late wake times were associated with an unfavorable activity and weight-status profile, independent of age, sex, household income, geographical remoteness and sleep duration.