Teenagers who begin school at 8:30 a.m. or later are much more likely to get the minimum recommended amount of sleep of eight hours, according to a new study published in the journal Sleep Health.
School start times after 8:30 a.m. were associated with increased time in bed, extending morning sleep by 27-57 minutes compared to teens with earlier school start times.
“Teens starting school at 8:30 a.m. or later were the only group with an average time in bed permitting eight hours of sleep, the minimum recommended by expert consensus,” said lead author Dr. Orfeu Buxton, associate professor of biobehavioral health at Pennsylvania State University. “Later school start times were associated with later wake times in our large, diverse sample.”
In contrast, teens with the earliest high school start times of 7:00-7:29 a.m. obtained 46 minutes less time in bed on average compared with teens with high school start times at 8:30 a.m. or later.
For the study, 413 teenagers completed an online daily diary each evening, beginning after 7:00 p.m. This included school days and non-school days during both the academic year and the summer, which was defined as September through May and June through August, respectively.
From each diary entry, researchers looked at the participants’ reports of the previous night’s bedtime, the time the teen woke up in the morning, whether or not the teen went to school, and the school start times.
Although teens with the earliest school start times were more likely to go to bed earlier than those who started at 8:30 a.m. or later, the teens with earlier start times still did not get the recommended amount of sleep. In fact, only those teens with an 8:30 a.m. start time or later actually got the recommended amount of sleep, Buxton said.
The findings help refute the common argument that later school start times will simply make teens stay up later, resulting in the same amount of sleep either way.
“The presumption is if you let kids start school later they will simply go to sleep later and still not get enough sleep,” Buxton said. “But that’s a hypothetical scenario. There wasn’t data to back that up.”
One potential reason for this may be that, despite going to bed earlier than their peers, teens with the earliest school start times don’t get enough sleep due to the anticipation of an early wake time the following morning, according to Buxton.
The researchers also point to previous evidence of students’ “sleep debt,” where teens make up for lost sleep on non-school days, causing them to wake up consistently and significantly later than they do on school days.
Both anticipation and sleep debt can misalign teens’ circadian clocks from expected early wake timing on school days, interfering with consistent sleep patterns.
Source: Penn State