When high schools start too early, sleep-deprived teenagers are more likely to crash their cars, suggests new research.
The study, which compared accident rates among teenagers in two adjacent counties in Virginia — one with schools that started extra early and one that started at a reasonable hour — confirms that teenagers are not designed to be morning people.
The finding also adds to a growing body of evidence that later start times can help adolescents earn better grades, get along better with their peers, gain control over their emotions, steer clear of drugs, avoid depression and even lower their risk of suicide.
"This study did not prove by any means that early high school start times led to increased rates of car crashes," instead it shows an association between early risers and car crashes, said Robert Vorona, a sleep doctor at Eastern Virginia Medical School in Norfolk, Virginia.
But combined with other research, he said, the evidence supports pushing school districts to change their hours of operation. "Early high school start times are problematic."
Vorona's youngest daughter inspired the new study. With classes starting at 7:20 a.m., she's up by 6 a.m. on weekdays. After-school activities, sports and homework make it hard for her to get in bed before 10. Already worried that his daughter might be sleep-deprived, Vorona discovered that high schools in a nearby county started more than an hour later. Immediately, he recognized a natural experiment waiting to be tested.
With the help of the Virginia Department of Motor Vehicles, Vorona collected data on the number of drivers between ages 16 and 18 in two counties: Virginia Beach, where high schools start at 7:20 a.m., and Chesapeake, where high schools start at 8:40 a.m. The DMV also provided information about crash numbers.
The data showed a clear difference between the two counties. Among students who started class close to dawn in Virginia Beach County, there were 65.4 car crashes for every 1,000 teen drivers. In Chesapeake County, there were just 46.2 crashes per 1,000 teen drivers, Vorona reported this week at SLEEP 2010, a meeting of the Associated Professional Sleep Societies. That's a 40 percent higher crash rate in the county where school starts earlier.
While the study doesn't prove that getting up early is what's causing kids to crash, other research supports the link.
A 2008 study in the Journal of Clinical Sleep Medicine, for example, found that when high schools in Fayette County, Kentucky, changed their start times from 7:30 a.m. to 8:30 a.m., teen car crash rates dropped by more than 16 percent.
Despite worries that later start times simply give teens an excuse to stay up even later, studies show that teenagers get more sleep when their schools start later, said Kyla Wahlstrom, director of the Center for Applied Research and Educational Improvement at the University of Minnesota, Twin Cities.
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Part of the reason is biological. Around puberty, the body's circadian rhythm shifts so that the brain doesn't get signals to sleep until 11 or 11:15 p.m. It doesn't matter how tired a kid is or what time he got up that morning.
"I've done focus groups with hundred and hundreds of kids over the years," Wahlstrom said. "They say, 'My mom says to go to bed, so I go in there and lay there and look at the ceiling until 11 o'clock, and all of a sudden I fall asleep.'"
The average teenager needs nine and a quarter hours of sleep, studies show. But with bodies that can't fall asleep until close to midnight and alarm clocks that sometimes go off before 6 a.m., it's no surprise that teens are falling asleep in class and behind the wheel.
Besides pressuring their school districts to change start-time policies, parents can encourage their teens to catch up on sleep when they can. It might help them to turn off their phones and computers by 10 p.m., so they can start winding down, Wahlstrom said.
And if your kid got far too few hours of shut-eye, don't let her drive to school, Vorona said. She may hate to take the bus, but at least she can safely nap on it.
© 2012 Discovery Channel