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Lack of Morning Light Keeping Teenagers Up at Night

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AP: Does your teen sit by the window in school? Maybe he or she should. A small (but provocative) experiment suggests that a lack of proper daylight might play a role in teenagers' out-of-whack sleep habits.

Teen sleeping in school

Sleep specialists say that too few teens get the recommended nine hours of shuteye a night. They are often unable to fall asleep until late, then struggle to awaken for early classes. Sleep patterns start changing in adolescence for numerous reasons, including hormonal shifts and increased school, work and social demands.

Researchers from the Rensselaer Polytechnic Institute wanted to find out what would happen if eleven eighth graders at Smith Middle School in Chapel Hill, North Carolina, suddenly lost exposure to a specific light wavelength. (They chose that school because it has lots of skylights; even when electric lighting is reduced, the energy-efficient classrooms are brighter than most.) 

From the time the students awoke until the time school ended, they wore special orange goggles that block short-wavelength "blue light" (but not the light necessary for proper vision). The researchers reported Tuesday that, after having blue light blocked for five days, the students' internal body clocks became upset -- delaying by half an hour their evening surge of a hormone called melatonin, which helps induce sleep.

Because daylight is the best source of those short-wavelength rays, teens who trudge to the bus stop before dawn -- or spend their days in mostly windowless schools -- probably suffer the same effect, says lead researcher Mariana Figueiro, of Rensselaer's Lighting Research Center in Troy, New York. "If you have this morning light, that is a benefit to the teenagers," she said. (According to Figueiro, a lack morning light isn't the only factor here: Too much evening light can add to the problem, too.)

Figueiro's study was a first step to test -- in real-world conditions -- findings from various sleep laboratories, which have long shown that a lack of light affects the 24-hour body clock and may play a role in teen sleep problems.

The study, published in the journal Neuroendocrinology Letters, is small, and didn't track students' sleep. It just tracked an early sign of change: the evening melatonin surge that typically precedes sleep by about two hours.

But though preliminary, the study should spur additional research on everyday light exposure, says sleep-medicine specialist Dr. Judith Owens, an associate pediatrics professor at Brown University. "There's a biologically based shift in the natural sleep onset and wake-up time," she notes. "I think what this study shows is that you can impact that shift with light manipulation. The major take-home message is to get natural light exposure early in the day."

Tuesday's report was part of a larger study involving a second school in New York; at that school, researchers are examining the effects of evening light exposure (computer and TV light, plus regular indoor lighting).

The research was funded by the National Institutes of Health and the U.S. Green Building Council.

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