according to results from a cohort study.
For their research published in JAMA Pediatrics, Rachel Widome, PhD, of the University of Minnesota, Minneapolis, and colleagues followed a cohort of students at five public high schools in suburban and rural Minneapolis, randomly selecting 455 (225 girls; mean age, 15 years) for wrist actigraphy to track sleep and activity.
The students were followed up over 2 years, from 2016 to 2018. Sleep and activity were monitored at baseline, at year 1, and at year 2. Baseline monitoring lasted a month, and each follow-up monitoring period lasted over 2 months.
Although all the high schools in the study had early start times when the study began, two moved within the first year to delay their starting times to after 8:30 a.m., after a decision by the local school district. The other three schools retained start times of 7:30 a.m. This allowed investigators to compare students’ sleep patterns between start times for an extended period.
Dr. Widome and colleagues found significant improvements in sleep at 1 year that did not attenuate in the second year. At the end of year 2, students in the delayed-start schools slept 43 minutes more on weeknights than their early-starting peers (95% confidence interval, 25-61, P < .001.) The investigators did not see significant between-group differences in weeknight bedtimes. On weekends, students in the delayed-start group slept a mean 34 minutes less at year 2 (95% CI, –65 to –3, P = .03) than their peers in the early groups.
The researchers described the study’s design, a natural experiment with long follow-up and objectively measured sleep data, as its key strength. “No previous studies have been performed of sufficient quality to conclude that later start times cause students to get more sleep and that this effect can be sustained,” they concluded.
In an editorial comment, Erika R. Cheng, PhD, and Aaron E. Carroll, MD, of Indiana University, Indianapolis, wrote that the study provides strong evidence that delaying early school start times “would help adolescents get the sleep they need to thrive,” and belies the commonly held argument that delayed school times would merely lead to them staying awake later on school nights.
Adolescents “experience natural circadian and physiological brain changes that shift their sleep preference to go to bed and wake up later than adults or younger children,” Dr. Cheng and Dr. Carroll noted, with 12th graders’ bedtimes typically after 11 p.m. on weekdays. Regardless, “more than 40% of high schools in the United States start before 8 a.m., and more than 20% of middle schools start at 7:45 a.m. or earlier.”
Dr. Cheng and Dr. Carroll cautioned that the population in this study comprised “relatively affluent students and schools,” and that there were “socioeconomic and racial differences in student characteristics between schools that did and did not adopt the later start times.” For instance, they noted, nearly 90% of students in the delayed-start schools reported having at least one college-educated parent, while in the comparison schools fewer than 75% did. Unmeasured characteristics associated with parent education may have “influenced the school district’s decision to delay schools’ start times and had an effect on student sleep duration.”
Dr. Widome and colleagues’ study was supported by a grant from the Eunice Kennedy Shriver National Institute of Child Health and Human Development; the authors received support from a grant from the Minnesota Population Center. One coauthor acknowledged receiving a consulting fee from Jazz Pharmaceuticals. Dr. Cheng and Dr. Carroll disclosed no relevant conflicts of interest.
SOURCES: Widome R et al. JAMA Pedatr. 2020 Apr 27. doi: 10.1001/jamapediatrics.2020.0344; Cheng ER, Carroll AE. JAMA Pediatr. 2020 Apr 27. oi: 10.1001/jamapediatrics.2020.0351.