Association of sleep timing and sleep variability with health-related outcomes in a sample of Brazilian adolescents.

Objectives: This cross-sectional study aimed to examine the relationships of sleep timing and sleep variability with depressive symptoms, health-related quality of life (HRQoL), daytime sleepiness, and body mass index (BMI) in adolescents.

Methods: Adolescents from three schools (n = 571, 56% female, 16.3 ± 1.0 years) had their sleep examined by actigraphy, their anthropometrics assessed, and answered a survey. Sleep timing was examined by combining groups of median-dichotomized onset and wakeup times (early onset and early wakeup; early onset and late wakeup; later onset and early wakeup; later onset and later wakeup); sleep variability was based on within-participant standard deviations of onset and wakeup; and sleep duration as the length of time between onset and wakeup. The sleep variables were separated for weekdays and weekend. Mixed linear models were fitted to compare each sleep variable with health-related outcomes.

Results: Higher values of daytime sleepiness were observed in adolescents from the late-early and late-late timing group during the week. Greater sleep midpoint and wakeup variability on weekdays were related with higher daytime sleepiness. Adolescents in the late-late and early-late groups showed higher daytime sleepiness. Increased of all sleep variability variables was related with greater daytime sleepiness. Higher depressive symptoms scores were found among adolescents in the late-early subgroup and with the increase of sleep variability. Participants with greater sleep onset variability and sleep midpoint variability reported less HRQoL.

Conclusions: Not only sleep duration, but sleep timing and variability also relate to health outcomes, and should be addressed by policies and interventions among adolescents.