THURSDAY, June 12 (HealthDay News) -- Teens whose high schools have a delayed start time sleep longer and report less daytime sleepiness, say researchers at Norwalk Hospital's Sleep Disorders Center in Connecticut.

The study included 259 high school students who reported sleeping about 7.03 hours per school night, with a mean bed time of 10:52 p.m. and a mean wake-up time of 6:12 a.m. when school started at 7:35 a.m.

After the school start time was switched to 8:15 a.m., the students' total sleep time on school nights increased 33 minutes, mainly due to a later rise time. Their bedtime on school nights was slightly later, and there was a slight decrease in weekend sleep time. After the change in school start time, more students reported having no problem with daytime sleepiness.

"Following a 40-minute delay in start time, the students utilized 83 percent of the extra time for sleep. This increase in sleep time came as a result of being able to 'sleep in' to 6:53 a.m., with little delay in their reported school night bedtime. This study demonstrates that students given the opportunity to sleep longer, will, rather than extend their wake activities on school nights," study corresponding author Dr. Mary B. O'Malley said in a prepared statement.

The research was expected to be presented at the annual meeting of the Associated Professional Sleep Societies, in Baltimore.

In other study results expected to be presented at the meeting, researchers found that teens who don't get enough sleep suffer lower school grades and lack of motivation and are increased risk for serious emotional and behavioral problems.

The University of Kentucky study of 882 high school freshmen found that they slept an average of 7.6 hours per school night, with 48 percent reporting less than eight hours.

The researchers found a strong association between hours of sleep per school night and GPA, level of motivation, emotional disturbance and attention-deficit hyperactivity disorder (ADHD). Each additional hour of sleep on school nights reduced the risk of scoring in the clinically significant range of emotional disturbance and ADHD by 25 percent and 34 percent, respectively.

"Since these findings are based on associations rather than direct experimental manipulation, they cannot conclusively prove that insufficient sleep causes a loss of motivation, poor grades, ADHD and emotional disturbance during adolescence," study author Fred Danner said in a prepared statement.

"These results, however, are consistent with a growing body of research that many adolescents do not get sufficient sleep, and that even mild chronic sleep deprivation has serious effects on their psychological functioning. Lack of sleep should no longer be considered a traditional adolescent rite of passage, because it can have serious consequences," Danner said.

More information

The Nemours Foundation has more about teens and sleep.

-- Robert Preidt

SIURCE: American Academy of Sleep Medicine, news release, June 9, 2008

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