MONDAY, June 6, 2005 (HealthDay News) -- If your high schooler isn't pulling down the grades you'd like, maybe you should blame it on sleep deprivation, and not on a lack of effort.
A new study found that teenagers lose nearly two hours of sleep each night during the school week. That sleep loss may be due to adolescents' increasingly busy schedules.
Or it may be because their circadian rhythms -- biological clocks -- seem to be set to a later schedule than younger children or adults. This makes it harder for teens to get to sleep early.
Couple those conflicted clocks with the early start times of many high schools, and the result is groggy teens who aren't performing at their best, particularly in the morning. But the researchers aren't sure if the loss of sleep during the week, or the disruption of the teens' circadian rhythm, is to blame.
"We found that there is much less sleep during school days. Teens lose about 10 hours of sleep per week, and on weekends they sleep more," said study co-author Margarita Dubocovich, a professor of molecular pharmacology, biological chemistry, psychiatry and behavioral sciences at Northwestern University's Feinberg School of Medicine.
Dubocovich said that later school start times might help improve academic performance.
The findings appear in the June issue of Pediatrics.
The researchers, including Dubocovich and a colleague from Feinberg, as well as a biology teacher and her students from Evanston Township High School in Illinois, had 60 high school seniors keep sleep/wake diaries during the summer and at various points throughout the school year.
A small group of 19 students was also exposed to bright light -- a synchronizing force for biological clocks -- for an hour and a half each school morning to try to readjust their clocks.
The investigators also assessed the children using a computer test to measure reaction times, and a paper-and-pencil exam to gauge mood and cognitive performance. The tests were given on four different days at three times throughout the day: 6:30 to 8:00 a.m.; 11:30 a.m. to 1:00 p.m.; and 3:00 to 4:30 p.m.
During August, when school wasn't in session, the teens averaged 8.7 hours of sleep a night. Once school began, that number dropped to an average of seven hours a night on weekdays. During summer weekends, the teens' sleep patterns were similar to summer weekdays. But once school began, that changed and the teens slept about 30 minutes more on school-year weekends than on summer weekends -- about 9 to 9.5 hours, according to Dubocovich.
Students performed better on the tests given in the afternoon than those given in the early morning. In the reaction test, students completed the test about 20 seconds faster in the afternoon than they had in the morning, the researchers said.
Exposure to light didn't appear to make a difference in performance or in students' energy levels, Dubocovich noted.
Dr. Irwin Benuck, an attending pediatrician at Children's Memorial Hospital in Chicago, called the research an interesting study that quantifies "a lot we already know."
He said he would have liked to have seen more information incorporated into the study, such as how much caffeine the children were drinking, or if they napped at all, or what they ate in the morning. These are all factors that could affect sleep patterns and school performance, he said.
Both Benuck and Dubocovich said schools should reevaluate start times, particularly for standardized achievement tests, which are often administered first thing in the morning.
In the meantime, both suggested encouraging your teen to get more sleep during the week.
"Kids are on a different sleep schedule than the rest of the world and they'll probably stay that way through college," Benuck said. "Parents should know that kids will rebound somewhat on the weekends."
"Allow your teens to sleep in on the weekends. They're not sleeping extra -- they're sleeping the normal amount of time they should be sleeping," Dubocovich said, adding that most teens need about nine hours of sleep a night.
The National Sleep Foundation offers tips on how teens can sleep better.