Two-year study finds later school start times improve student sleep

Over half of US teenagers sleep less than seven hours each night, and there is increasing evidence these adolescent sleep deficits affect everything from general health to academic performance. A new study, led by researchers from the University of Minnesota, followed hundreds of students across five high schools for two years and found later school start times increase overall sleep durations.

For nearly a decade now many researchers have been pushing for later school start times in the United States. Back in 2014, the American Academy of Pediatrics recommended middle and high schools start no earlier than 8.30am, yet a study published that same year found over 90 percent of US high school students started before that time.

Around eight hours of sleep every night is the general recommendation for healthy adults, however, teenagers need a little more than that. The various biological changes going on in a growing adolescent body result in wonky circadian rhythms. Teenagers generally become sleepy much later in the evening than adults, plus, they need between eight and ten hours to maintain optimal physical and cognitive health.

In this new study, a US research team offers the most comprehensive investigation conducted to date into the sustained relationship between later school start times and teenager sleep quality. The study began by recruiting 455 grade nine students from five high schools. At the beginning of the study in 2016, two of the schools pushed back their start times, by 50 and 65 minutes respectively, while the other three continued with the regular 7.30am start time.

At the end of the two-year study the results revealed those students at schools with later start times experienced an average of 43 minutes more sleep than their early-starting peers. This extension in sleep duration is important, because the primary argument often waged against later school start times is the suggestion students would simply stay up later into the night if school started later in the morning.

In fact, the study found no relative difference in sleep onset times between the early and late school starters, across the entire two year study period. So on average, teenagers went to sleep at the same time regardless of starting school at 7.30am or 8.30am.

“Furthermore, concurrent with the increase in school night sleep duration, those attending delayed-start schools had a decrease in weekend night sleep duration, suggesting lesser accumulated sleep debt with the later start times,” the researchers write in the study. “Sleep fragmentation, sleep efficacy, and sleep latency onset appeared to be minimally affected or unaffected by the shift to a later start time.”

Unlike some smaller prior studies, this new research did not examine any effects of the school start time intervention beyond overall sleep duration. So although there is prior evidence more sleep in adolescents can lead to improved academic performance, this new study is not built to address that effect.

In an accompanying editorial discussing the study, pediatric researcher Erika Cheng and JAMA Pediatrics associate editor Aaron Carroll point out the study offers significant and robust evidence that delaying school start times can result in better adolescent sleep duration. Cheng and Carroll, who did not work on the new study, refer to a notable volume of research linking mental health problems and poor academic performance in teenagers to insufficient sleep duration.

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

The new research was published in the journal JAMA Pediatrics.