December 13, 2017
2 min read

Later school start times allow teens to get 8 hours of sleep

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High school students who start school at or after 8:30 a.m. are more likely to spend more time in bed and are most likely to achieve a full 8 hours of sleep, according to a study published in Sleep Health.

“Melatonin secretion patterns, a reliable indicator of circadian timing, are delayed in both onset and offset relative to the dark/sleep period during puberty, triggering relatively later bedtimes and desired later wake times in teens,” Nicole G. Nahmod, BS, from the department of biobehavioral health at Pennsylvania State University, and colleagues wrote. “These physiological changes in circadian timing are incompatible with the daily life contexts of contemporary U.S. teens.”

Nahmod and colleagues noted that several factors — including social pressures, schoolwork, employment, familial schedules, extracurricular activities and electronic devices — may further interrupt circadian patterns of adolescents.

To examine the relationship between adolescent bedtimes, wake times, time spent in bed and high school start times, the researchers conducted a study in which adolescents residing within urban environments in 20 cities completed daily diary entries. This study fell within the prospective Fragile Families and Child Wellbeing Study.

Teenagers included in the study were instructed to complete one or more diary entry daily for 7 consecutive days. The researchers analyzed entries made on 1,555 school days (3.8 ± 1.6 entries per person). School start times were sorted into cohorts, with 15% starting between 7:00 and 7:29 a.m., 22% starting between 7:30 and 7:59 a.m., 35% starting between 8:00 and 8:29 a.m., and 28% starting at or after 8:30 a.m.

Nahmod and colleagues used multilevel modeling to assess the connections between wake time, bedtime and time spent in bed. They then used models to consider age, sex, race/ethnicity, household income, caregiver’s education and school type.

Of the 413 adolescents included in the study, those who started school between 7:00 and 7:29 a.m. spent 46 minutes less in bed on average than those who started at or after 8:30 a.m. (P < .001). A dose-response relationship was observed by Nahmod and colleagues regarding earlier school start times and less time spent in bed. This, according to the researchers, was mostly due to the earlier wake times associated with earlier start times (P = .05). Adolescents who began school at or after 8:30 a.m. were more likely to spend more time in bed and had their sleep time increased by 27 to 57 minutes (P <.05).

The researchers note that high school students who begin school at or after 8:30 AM were the only cohort that spent enough time in bed to reach the recommended minimum of 8 hours of sleep.

“The presumption is if you let kids start school later, they will simply go to sleep later and still not get enough sleep,” Orfeu M. Buxton, PhD, associate professor of biobehavioral health at Pennsylvania State University, said in a press release. “But that is a hypothetical scenario, and there was not data to back that up.” – by Katherine Bortz

Disclosures: The authors report no relevant financial disclosures.