Bright E-Readers Before Bedtime Can Impact Sleep, Overall Health

It's not uncommon to read a good book snuggled under the covers to put you to sleep, but a new study shows that bright e-Readers, also known as light-emitting electronic devices (LE-eBook), before bedtime can impact your sleep cycle and overall health.

"We found the body's natural circadian rhythms were interrupted by the short-wavelength enriched light, otherwise known as blue light, from these electronic devices," Anne-Marie Chang, a corresponding author of the study, said in a press release. "Participants reading an LE-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."

E-Readers emit blue light, which suppresses melatonin, impacts the circadian clock and increases alertness, according to previous research. But until now, researchers hadn't delved into its effect on the circadian clock, which synchronizes the daily rhythm of sleep to external environmental time cues. And with technology like tablets and Kindles more popular these days, their role in sleep deficiency is of more concern to researchers.

The findings were published in the journal Proceedings of the National Academy of Sciences.

During the study, 12 participants read LE-e-Books on an iPad for four hours before bedtime each night for five consecutive nights, repeating the process with printed books. Although iPads were the main focus of the research, Chang and her colleagues at Brigham and Women's Hospital (BWH) also measured other e-Readers, laptops, cell phones, LED monitors, and other electronic devices, all emitting blue light.

Those participants that read on the iPad took longer to fall asleep, were less tired in the evening and sleepier in the morning, and spent less time in REM sleep. Not to mention they had a circadian rhythm that was delayed by more than an hour, and reduced secretion of the hormone melatonin, which normally rises in the evening and induces sleepiness.

"In the past 50 years, there has been a decline in average sleep duration and quality," said researcher Charles Czeisler. "Since more people are choosing electronic devices for reading, communication and entertainment, particularly children and adolescents who already experience significant sleep loss, epidemiological research evaluating the long-term consequences of these devices on health and safety is urgently needed."

Light exposure at night from these electronic devices may also be linked to the increased risk of breast cancer, colorectal cancer and prostate cancer.

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