By LEE BOWMAN
Scripps Howard News Service
November 01, 2005
While much of the blame for the cycle has been put on teens having too much to do at night and school start times being too early, researchers have found a physical reason for the delay in bedtimes.
A new study suggests that, as children mature, the chemically driven pressure to sleep builds up more slowly. As a result, teens just don't get sleepy until later in the evening. The work was reported Tuesday in Sleep, the journal of the American Academy of Sleep Medicine.
Earlier studies have shown that changes in the body's internal clock - variations that accompany puberty - contribute to delayed sleep. But the new research finds that there's also a delay in the buildup of sleep needed in adolescents, even in the face of sleep deprivation.
"We've found another part of the story - the mechanism in the brain that builds up sleep pressure is working at a different rate in adolescents than in pre-pubescent children," said Mary Carskadon, a co-author of the study. She is director of the Bradley Hospital Sleep Laboratory in Providence, R.I., and a professor of psychiatry and human behavior at Brown University Medical School.
The study involved 13 boys and girls between ages 10 and 16; seven were pre-teens, the rest teenagers. All underwent 36 hours of sleep deprivation in a lab as their brainwaves were monitored.
A slower buildup of sleep pressure in mature adolescents was seen in their levels of slow-wave activity, which tend to be high when the need for sleep is the greatest.
"When children are little, their sleep pressure rises faster so they fall asleep early, but when it's slower, like it is for teenagers, it's harder to get to sleep," Carskadon said.
Carskadon has also studied how teen brains secrete the sleep-regulating hormone melatonin. She found that the older teens are, the later their production of the hormone kicks in during the evening, and the later in the morning production shuts down.
She and co-authors Dr. Oskar Jenni and Peter Acherman of the University of Zurich suggest that the change in adolescent sleep cycles is just another step toward adulthood. "We propose that the higher tolerance for prolonged waking may prepare children for adult lifestyles and for performing tasks under sleep deficits that are common in adults of modern societies," they wrote.
But the National Sleep Foundation also notes that most studies show adolescents need at least as much sleep as they did as children, maybe more. Studies indicate that 9- and 10-year-olds do fine with about eight hours of sleep a night; teens seem to need nine to nine-and-a-half for their best performance.
Teen sleep deficits and how they can impact both school performance and safety is the main force behind the foundation's campaign to encourage school systems around the country to consider later start times for high schools.
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