Factors associated with late bedtimes, early wake-up times, and short sleep in adolescents on school nights.

Introduction: Identifying factors that contribute to inadequate sleep in adolescents is important for developing interventions to improve sleep, learning, and well-being. The goal of our study was to estimate the strength of associations of individual and environmental factors with adolescents' sleep timing and duration. Methods: Daily sleep onset, offset, and duration were measured by actigraphy in 133 Singaporean adolescents (13-18 years; 67 girls) during a typical school week in which individual students often had more than one school start time. Daily diaries recorded behaviors before and after nocturnal sleep. Linear mixed models were used to estimate associations of age, sex, ethnicity, socioeconomic status, chronotype, night of the week, bedtime reason, morning get-ready time, commute time, and school start time with nocturnal sleep. Results: Later sleep onset was associated with older age, later chronotype, and homework/studying at bedtime. Earlier sleep offset was associated with longer get-ready and commute times and earlier school start time. Shorter sleep was associated with older age, later chronotype, homework/studying at bedtime, and earlier school start time. Adolescents obtained 45 min less sleep when their main reason for bedtime was finishing homework/studying versus feeling tired or sleepy. They obtained 50 min more sleep when school started from 08:30 to 08:59 am versus from 07:30 to 07:59 am. Conclusions: Multiple factors influence adolescents' sleep on school nights. Modifiable factors that were strongly associated with short sleep included homework/studying at bedtime and early school start times. Avoiding schoolwork near bedtime and delaying school start time are potential strategies for improving sleep in adolescents.