You there curled up late at night with your smartphone, tablet or e-reader. Having trouble sleeping? It may be that exposure to the device's light is messing with your circadian clock.
According to Researchers at Penn State, study participants took nearly 10 minutes longer to fall asleep and had a significantly lower amount of rapid eye movement (REM) sleep after reading from a light-emitting e-reader than they did after reading from a printed book.
Exposure to light during evening and early nighttime hours suppresses release of the sleep-facilitating hormone melatonin and shifts the circadian clock, making it harder to fall asleep at bedtime. And electronic devices emit a form of light that “is different from natural light in composition, having a greater impact on sleep and circadian rhythms,” says Anne-Marie Chang, assistant professor of bio-behavioral health, who led the project.
Chang and colleagues observed 12 adults for two weeks, comparing when the participants read from an iPad before bedtime to when they read from a printed book before bedtime. The researchers monitored the participants' melatonin levels, sleep and next-morning alertness, as well as other sleep-related measures.
“Our most surprising finding was that individuals using the e-reader would be more tired and take longer to become alert the next morning,” explains Chang. “This has real consequences for daytime functioning, and these effects might be worse in the real world as opposed to the controlled environment we used.”
Chang anticipates that the findings will lead to further investigation of the effects of light-emitting technologies on sleep, including, for example, the timing of exposure to this light at different times of day.
“We hope this will lead to the development of technological devices that are more 'sleep compatible,'” she says. “We live in a sleep-restricted society in general — it is important to further study the effects of using light-emitting devices, especially before bed, as they may have longer term health consequences than we previously considered.”
Source: Anne-Marie Chang, Penn State University
Writer: Elise Vider