The transition of sleep-wake patterns in early adolescence.

STUDY OBJECTIVE: To examine the relationship between school grade level and sleep-phase preference in early adolescence.

DESIGN: A school-based cross-sectional study using a Sleep Habit Questionnaire.

SETTING: NA.

PARTICIPANTS: One thousand five hundred and seventy-two students, grade 4 to grade 8, from 3 junior high schools and 3 elementary schools in Taipei were recruited using multistage sampling method. The response rates were 98.4% (1547) for participants and 95.9% (1509) for their parents.

INTERVENTIONS: NA.

MEASUREMENTS AND RESULTS: Each student participant completed a Sleep Habit Questionnaire, including sleep schedules, the Morningness/Eveningness (M/E) scale, the Pubertal Developmental Scale, and the Sleepiness Scale. The morning (N = 367) and evening (N = 364) groups were operationally defined as participants with the top 25% and the bottom 25% of the M/E score, respectively. A mixed model was used in data analysis to address the cluster effects arising from the school-based study. We found that the M/E score decreased and the proportion of the evening type increased across grade 4 to grade 8. The evening type was associated with decreased nocturnal sleep and later bedtimes and rise times, as well as with increased daytime sleepiness and compensation for sleep on weekends.

CONCLUSIONS: Our findings support the hypothesis that school grade level is significantly associated with the transition to evening type in early adolescence. We report that environmental factors may play a more important role than biologic factors, such as age, sex, and pubertal development, in the transition from morning type to evening type at early adolescence. Future longitudinal study is necessary to determine the trajectories of sleep-wake patterns in adolescents and their predictors.