Does school start time affect sleep patterns among adolescents?

By Dr. Ananya Mandal, MDApr 27 2020

Researchers looked at the positive and negative effects of the early or late school start time on sleep quality and duration of adolescents. Their study titled, “Association of Delaying School Start Time With Sleep Duration, Timing, and Quality Among Adolescents,” was published in the latest issue of the journal JAMA Pediatrics.

Study: Association of Delaying School Start Time With Sleep Duration, Timing, and Quality Among Adolescents. Image Credit: Sabphoto / Shutterstock

What was this study about?

This study was led by Rachel Widome, Ph.D., M.H.S., of the University of Minnesota School of Public Health in Minneapolis. The researchers wrote that the importance of the study lay in the fact that sleep could be considered a “resource” and is closely associated with “health and well-being.” The researchers wrote that it is common to find adolescents often getting less amount of sleep, and most of it is of poor quality.

They wrote that the objective of this study was “to examine how delaying school start time is associated with objectively assessed sleep duration, timing, and quality in a cohort of adolescents.”

What was done in this study?

This was essentially an observational study. This meant that the study was to observe the effects of school time on sleep schedules of adolescents. The team essentially compared the effects of school start time (early or delayed) with how long and how well the high school students slept.

The team wrote that district authorities had initiated changes in the school start times of five public high schools in the metropolitan regions of Minneapolis and St Paul, Minnesota. For this study, the team enrolled a total of 455 students who were followed up from grade 9 to grade 11. The study start date was between May 3 and June 3, 2016, when the recruitment of the participants took place. Study follow up ended between March 15 and May 21, 2018. Gathered data were analyzed from February 1 to July 24, 2019.

In the study, the five participating schools started early between 7.30 AM and 7.45 AM at the beginning of the study in 2016. At first follow up in 2017, two of the five schools delayed their start time by 50 and 65 minutes respectively. The three other schools stuck with the 7.30 AM start for the entire duration of the study.

To measure quality and duration of sleep among the study participants, the students were all given wrist monitors called actigraphy instruments—these measure several parameters such as sleep duration, time of sleep, quality of sleep, etc. At the end of the data collection, the team used statistical tests such as “difference-in-difference design, linear mixed-effects models” to find associations between changes in school start times and sleep time, duration, and quality among the participants.

What was found?

Among the 455 students participating in the study, there were 225 girls (49.5 percent). This meant that both girls and boys were almost equally represented. Their average age at the start of the study was 15.2 years.

Results showed that students who attended delayed start schools had an additional average of 41 minutes of night sleep at first follow up in 2017 and extra 43 minutes of night sleep at the second follow up in 2018. These students who started school later, due to their lack of sleep deficits throughout the school week, needed less extra sleep over the weekends to make up for the sleep loss.

Fears proved wrong, and it was found that contrary to popular belief, delayed school time does not translate to falling asleep later among the teenagers on school nights. There as an average of 24 minutes and 34 minutes of delay in falling asleep on a school night among children who attended delayed start school at first follow up and second follow up respectively. Quality of sleep, the onset of sleep was also not different among the two groups of students (delayed time and early start time school students). Sleep fragmentation index refers to disturbed sleep. It was seen that adolescents attending both types of schools had no difference in their sleep fragmentation index.

The researchers wrote, “Differences in differences for school night sleep onset, weekend sleep onset latency, sleep midpoints, sleep efficiency, and the sleep fragmentation index between the two conditions was minimal.”

Conclusions and importance of this study

The team wrote that delaying high school start time can increase the school night sleep time among teenagers and also lessen their sleep requirements over the weekends. They wrote, “These findings suggest that later start times could be a durable strategy for addressing population-wide adolescent sleep deficits.” They call it (delaying school start time) as one of the “readily deployable sleep promotion interventions” that can allow teenagers a chance to adopt healthy sleep habits. They call for more research in this area to see if delaying school start time could improve sleep patterns and also have an effect on the academic performances of the students. The authors wrote, “The present study’s results suggest that later start times could be a durable and transformative strategy for dealing with the epidemic sleep insufficiency among adolescents.”

Accompanying expert comment

In an accompanying editorial in the same issue of the journal, titled, “Delaying School Start Times to Improve Population Health,” researchers Erika R. Cheng and Aaron E. Carroll discussed the merits of this study.

They write that poor sleep duration and quality among teenagers is a significant problem and can lead to problems in several aspects of daily lives such as “poor memory consolidation, less sustained attention, decreased academic performance, physical and mental health problems, and more risk-taking behavior”. They wrote that the National Heart, Lung and Blood Institute, the American Academy of Sleep Medicine, and the American Academy of Pediatrics recommend that adolescents need from 8 to 10 hours of sleep daily for optimum health. Most teenagers, they wrote, tend to get an average of fewer than 7 hours of sleep on a school night and less than 8 hours of sleep over the weekends.

They explained that over 40 percent of schools in the United States began before 8 AM, and 20 percent of middle schools start at 7.45 AM, and early starts have been associated with sleep deficits among children. Talking about this study, they write Widome et al., “…followed up participants longitudinally for two years” and thus could look at the natural course of things. Their use of wrist actigraphy also allowed them to measure the sleep parameters accurately.

The editorial says in conclusion, “We often blame adolescents for their not getting enough sleep, but much of that is not their fault—it is ours. We set the school start times, mostly to fit our work schedules. Pushing back school start times might be inconvenient. Still, it is a mutable, cost-effective, population-level strategy that would improve the lives of many, if not most, adolescents in the United States.”