Results from high school senior sleep/wake diaries kept for the study also showed that adolescents lost as much as two hours of sleep per night during the school week, but weekend sleep times during the school year were similar to those in summer.
The study was a collaborative project involving researchers at the Feinberg School of Medicine and the Center for Sleep and Circadian Biology at Northwestern University and faculty, students and parents from Evanston Township High School, Evanston, Ill. The students were advanced placement biology students who helped conduct the study and analyze the collected data.
Martha Hansen, advanced placement biology teacher and current science department chair at Evanston Township High School, headed the project in collaboration with Margarita L. Dubocovich, professor of molecular pharmacology and biological chemistry and of psychiatry and behavioral sciences, Feinberg; and Phyllis C. Zee, M.D., professor of neurology, Feinberg.
The study assessed the impact of sleep loss after the start of school on cognitive performance and mood and examined the relationship of weekday to weekend sleep in adolescents.
The study also showed that exposure to bright light in the morning did not modify students' sleep-wake cycle or improve daytime performance during weekdays probably because of their strict school schedule. All students performed better in the afternoon than in the morning. Students in early morning classes reported being wearier, less alert and having to expend greater effort. Potential solutions to this problem could be solved by changing school start times and by giving standardized tests later in the day, the authors suggested.
For example, classes at Evanston Township High School start at 8:05 a.m. and run until 3:35 p.m. - one of the longest school days in Illinois. Many high schools in the country have start times of 7:15 or 7:30 a.m. In addition, almost all standardized tests in high school begin at 8 a.m.
Since this is when adolescents show their poorest performance levels, a change is clearly needed and would be relatively easy to negotiate, the researchers suggest.
While the authors emphasized that more research on adolescent circadian rhythms is needed, they also believe that all groups dealing with adolescents - pediatricians, parents, teachers and teenagers themselves - need to be aware of adolescents' lifestyle patterns and the unusual weekday/weekend sleep phenomena.
"Knowledge of adolescent circadian rhythms could promote better family relationships if parents understood that sleeping late on weekends is part of their children's in-born cycle and not 'lazy' or antisocial behavior," the researchers said. Finally, this sleep study forged collaboration between high school students and faculty where everyone learned and benefited from the experience.
"Students were able to learn about the process of collecting and analyzing data and to discover more about the fascinating topic of themselves," the authors said.
Other researchers on the study were Imke Janssen, statistician and Evanston Township High School parent; and Adam Schiff, a former Evanston Township High School student, currently in medical school.