Objectives: Sleep duration and physical activity decline with age during adolescence. Earlier school schedules may contribute to these declines. The aim of this longitudinal study was to track changes in sleep and activity of Icelandic youth from primary to secondary school and compare students who enrolled in secondary schools with traditional and college-style schedules.
Methods: We measured free-living sleep and activity with wrist actigraphy and body composition by dual-energy x-ray absorptiometry in 145 students at age 15 and age 17, when 58% attended schools with college-style scheduling. Differences from 15 to 17 and between students of different school structures were assessed with mixed-effect models.
Results: Actigraphs were worn for 7.1 ± 0.4 nights at 15 and 6.9 ± 0.4 nights at 17. Overall, sleep duration decreased from 6.6 ± 0.7 h/night to 6.2 ± 0.7 h/night from age 15 to 17 (P < .001). Students with traditional schedules reduced school-night sleep duration 26 min/night at follow-up (P< .001), while sleep duration did not change for college-style students. All students went to bed later on school nights at follow-up, but only college-style students rose later. Sleep efficiency and awakenings did not differ by schedule-type. Neither sex changed body fat percentage, but average school-day activity decreased by 19% (P< .001) on follow-up and did not differ by schedule-type.
Conclusions: Over the 2-year period, adolescents decreased weekly sleep duration and activity, but only those continuing traditional schedules reduced school-night sleep. This suggests greater individual control of school schedule may preserve sleep duration in this age group, which may be beneficial during the transition into adulthood.
Keywords: Accelerometer; Adolescents; Body composition; Physical activity; School schedule; Sleep duration.
Published by Elsevier Inc.