Dec 26, 2014 03:09 AM EST By J Baulkman, UniversityHerald Reporter

New research suggests that e-readers and tablets could be harming your quality of sleep.

Researchers from Penn State University found that 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.

"Electronic devices emit light that is short-wavelength-enriched light, which has a higher concentration of blue light -- with a peak around 450 nm -- than natural light," researcher Anne-Marie Chang, assistant professor of biobehavioral health, said in a statement. "This is different from natural light in composition, having a greater impact on sleep and circadian rhythms."

For the study, researchers observed 12 adults for two weeks, comparing when the participants read from an iPad, serving as an e-reader, 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. The researchers collected blood samples from the readers hourly to measure melatonin.

They found that 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 print book.

"Our most surprising finding was that individuals using the e-reader would be more tired and take longer to become alert the next morning," Chang said. "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 said 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."

The findings are detailed in the journal Proceedings of the National Academy of Science.

See Now: Covert Team Inside Newsweek Revealed as Key Players in False Human Trafficking Lawsuit