Being plugged-in has become the norm. We use cell phones, tablets, e-readers and other mobile electronic devices constantly. While these devices make so much easier — from gathering information on the go to shopping to staying in touch with family — consistent and long-term exposure to such devices is not so good for our health.

A new study focusing on light-emitting electronic devices finds that use before bedtime can make it hard to fall asleep.

Our circadian rhythms are the basis for the internal clock that regulates our daily cycles of sleep and waking, using cues from the environment, such as light. According to researchers from Brigham and Women's Hospital, when we read eBooks or stare at other screen-based apps before bedtime, it can negatively affect overall health and disrupt this circadian clock.

The researchers found that the body's natural circadian clock is interrupted by the short-wavelength blue light that is emitted in high amounts by several mobile electronic devices, including eBooks. These impacts could be observed in several ways.

“Participants reading an [light-emitting] eBook took longer to fall asleep and had reduced evening sleepiness, reduced Melatonin secretion, later timing of their circadian clock and reduced next-morning alertness than when reading a printed book,” said Anne-Marie Chang, one of the authors of the study, and associate neuroscientist in BWH's Division of Sleep and Circadian Disorders, in a statement.

The team found that individuals reading on electronic devices took longer to fall asleep, were less sleepy in the evening, and spent less time in REM sleep.

Other studies had found that blue light suppresses melatonin and can impact the circadian clock, but it was unclear exactly how these changes operated during sleep. Given the commonplace use of these light emitting devices, the researchers were interested in directly measuring changes in sleep quality. They included a wide variety of blue light-emitting devices such as iPads, eReaders, laptops, cell phones, and LED monitors.

Participants in the study read for four hours every night, using either an electronic light-emitting reading device or printed book. Individuals reading on electronic devices took longer to fall asleep, were less sleepy in the evening, and spent less time in REM sleep.

Those exposed to blue light secreted less melatonin, a hormone which normally rises in the evening and plays a role in the sensation of sleepiness. Electronic devices caused a delay in circadian rhythms, and those using them reported feeling sleepier and less alert the following morning, despite eight hours of sleep.

The researchers argue that this lack of good quality sleep is a problem affecting us as a population.

“In the past 50 years, there has been a decline in average sleep duration and quality,” said Charles Czeisler, another researcher and chief of the BWH Division of Sleep and Circadian Disorders.

As more people are choosing electronic devices for reading, communication and entertainment, particularly individuals already experiencing significant sleep loss, further research evaluating the long-term consequences of these devices on health and safety is urgently needed. The last thing most of us need is another way to undermine the quality of the sleep we give our bodies.

The study is published in Proceedings of the National Academy of Sciences.