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Explainer: The teenage body clock

Around puberty, a change in the body clock of adolescents and teens makes it hard for them to fall asleep as early as they used to

Researcher Mariana Figueiro of Rensselaer Polytechnic Inst. helps a middle school student test a pair of orange goggles in an early study showing the connection between sleep problems and lack of exposure to morning light. Credit: Lab of Mariana Figueiro/ RPI

Somewhere around puberty, something happens in the timing of our biological clock. That clock pushes forward, so adolescents and teens are unable to fall asleep as early as they used to. At bedtime, their bodies may be pushing them to stay up for several hours more.

This shift is natural for teens. But staying up very late and sleeping late can push a teen’s body clock out of sync with the natural outdoor cycle of light and darkness. It can also make it hard for teens to get out of bed in the morning and may bring other problems, too.

Teenagers are put in a kind of a gray cloud when they don’t get enough sleep, says Mary Carskadon. She’s a sleep researcher at Brown University in Providence, R.I. Too little sleep can affect a teen’s mood and ability to think or learn.

But just like an alarm clock, the body’s internal clock can be reset. In fact, it automatically resets itself every day. How? By using the light entering our eyes.

The body’s clock is very sensitive to blue light — the color of the morning sky. Exposure to morning sunlight is best for synchronizing the body’s clock with the Earth’s natural 24-hour cycle of light and dark.

If you wake early and get outside, the body’s master clock tends to shift earlier, says Mariana Figueiro, a scientist at Rensselaer Polytechnic Institute in Troy, N.Y. That means you’re alert when it is light outside and sleepy when it’s dark.

The problem is, tweens and teens may have limited exposure to the morning light. Often, they are on a bus or in class during the peak morning hours. So to get morning light during the school year, researchers suggest, these students should use a morning break — say, sometime around 9 a.m. or 10 a.m. — to go outdoors or look out a window. Also, they should try to spend a few minutes outside before going to school.

However, for the same reason that blue light is helpful in the morning, it can be disruptive to the body clock when eyes encounter it at night. Computer screens, TVs and other electronic devices all emit some blue light. So their use at night could unknowingly push tired students to stay up even later.

But here too there is a simple solution: wearing orange goggles. They may look dorky, but they’ll block out blue light. The trick is to wear them in the evening, not in the morning. Worn in the evening, blue-blocker goggles can protect students from getting the signal that it’s daytime when in fact the body should be winding down for sleep.

Power Words

body clock (also known as biological clock) A mechanism present in all life forms that controls when various functions such as metabolic signals, sleep cycles or photosynthesis should occur.

sync (short for synchrony) Work together in harmony at the same time or rate, like in a marching band.

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