Researchers followed more than 1 000 Philadelphia-area teenagers from their
freshman through senior years of high school. Every six months, the teens
reported their sleep patterns.
The results showed that each additional hour of sleep per night was
associated with reduced body-mass index (BMI), a measure of body fat based on
height and weight. The reduction was greatest in those with higher BMIs, meaning
they were more overweight.
Based on their findings, the researchers from the University of Pennsylvania
Perelman School of Medicine suggested that increasing sleep from eight to 10
hours a night at age 18 could lead to a 4 percent reduction in the number of
overweight or obese American teens. That would translate to about 500,000 fewer
"Educating adolescents on the benefits of sleep and informing them of sleep
hygiene practices has shown to have little impact on adolescent sleep duration,"
lead author Jonathan Mitchell, a postdoctoral fellow in the Center for Clinical
Epidemiology and Biostatistics, said in a Penn Medicine news release.
"One possible solution could be for high schools to delay the start of the
school day," Mitchell said. "Previous research has shown that delaying the start
of the school day even by 30 minutes results in a 45-minute per day increase in
sleep. Since our study shows increasing sleep by an hour or more could lead to a
lower BMI, delaying the start of the school day could help reduce obesity in
Although the research suggested an association between more sleep and a lower
BMI, it didn't establish a cause-and-effect relationship.
The Nemours Foundation offers advice on how teens can achieve
and maintain a healthy weight.
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