Blue light exposure boosts stress hormone response in sleep-deprived teens

According to the Centers for Disease Control and Prevention (CDC; Atlanta, GA), almost 70 percent of adolescents get less than 8 hours of sleep on school nights, which has been linked with depression, behavior problems, poor performance at school, drug use, and automobile accidents. Recognizing this, researchers from the Lighting Research Center (LRC) at Rensselaer Polytechnic Institute (RPI; Troy, NY) have shown that exposure to morning short-wavelength blue light has the potential to help sleep-deprived adolescents prepare for the challenges of the day and deal with stress.

Levels of cortisol, a hormone produced by the adrenal gland, follow a daily 24-hour rhythm. Cortisol concentrations are low throughout the day, reaching a broad minimum in the evening before rising slowly again throughout the night. In addition to this gradual elevation of cortisol at night, cortisol levels rise sharply within the first 30 to 60 minutes after waking. This is known as the cortisol awakening response (CAR). In nocturnal animals, the cortisol spike occurs at night, at the start of activity. It appears to be associated with the time of transition from rest to activity, upon waking. A high CAR has been associated with better preparedness for stressful and challenging activities.

“The present results are the first to show that low levels of short-wavelength light enhance CAR in adolescents who were restricted from sleep,” says Mariana Figueiro, associate professor and director of the LRC Light and Health Program. “Morning light exposure may help to wake up the body when it is time to be active, thus preparing individuals for any environmental stress they might experience.”

Short-wavelength light has been shown to maximally suppress production of nocturnal melatonin and phase shift the timing of the biological clock. The effect of short-wavelength light on other biomarkers has not been widely studied.

The study, which was funded by Sharp Laboratories of America, included three overnight sessions, at least one week apart. All participants wore a Dimesimeter on a wrist band to measure light exposure and to verify the regularity of their activity/rest periods during the three-week study. The Dimesimeter is a small, calibrated light meter device developed by the LRC that continuously records circadian light and activity levels. During the study, adolescents aged 12 to 17 years went to sleep at 1:30 a.m. and woke up at 6:00 a.m., a 4.5-hour sleep opportunity. Each week, participants either experienced morning short-wavelength blue light (40 lux of 470 nm light) or remained in dim light.

“We found that exposure to short-wavelength blue light in the morning significantly enhances CAR in sleep deprived adolescents, more so than dim light,” says LRC director and professor Mark S. Rea. “Morning exposure to short-wavelength light may be a simple, yet practical way to better prepare adolescents for the challenges of the day.”

The work has been published in the International Journal of Endocrinology; for more information, please visit www.hindawi.com/journals/ije/2012/301935/.

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