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Beware of Blue Light Before Sleep

Can the way you read before bedtime affect the quality of your sleep?

Recent research from Brigham and Women’s Hospital (BWH) suggests that the use of light-emitting electronic devices – tablets, some e-readers, smart phones, and laptops – in the hours before bedtime can negatively impact overall health, alertness, and the circadian clock, which synchronizes the daily rhythm of sleep to external environmental cues.

“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,” said Anne-Marie Chang, PhD, corresponding author and associate neuroscientist in BWH’s Division of Sleep and Circadian Disorders. “Participants reading a light-emitting e-book took longer to fall asleep and had reduced evening sleepiness, reduced melatonin secretion, later timing of their circadian clock, and reduced next-morning alertness.”

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Studies have shown that blue light has adverse effects on sleep-related processes.

What does the research show? 

During the two-week inpatient study, 12 participants read e-books on a light-emitting iPad for four hours before bedtime each night for five consecutive nights and followed the same regimen with printed books. Researchers found that participants reading on an iPad took longer to fall asleep and spent less time in REM sleep; had reduced secretion of melatonin, a hormone that normally rises in the evening and plays a role in inducing sleepiness; had a delayed circadian rhythm of more than an hour; were less sleepy before bedtime; and were sleepier and less alert the following morning.

This preliminary research supports previous studies demonstrating blue light’s adverse effects on sleep-related processes. Poor-quality sleep, in turn, can have a significant impact on physical health, including an increased risk of heart disease, diabetes, obesity, and certain cancers.

In this video, Charles A. Czeisler, MD, PhD, Chief of the Division of Sleep and Circadian Disorders at BWH, explains how artificial light can disrupt sleep patterns.

“In the past 50 years, there has been a decline in average sleep duration and quality,” said Dr. Charles Czeisler, Chief of BWH’s Division of Sleep and Circadian Disorders. “Since more people are choosing electronic devices for reading, communication, and entertainment, particularly children and adolescents who already experience significant sleep loss, research evaluating the long-term consequences of these devices on health and safety is urgently needed.”

*Although iPads were the only light-emitting electronic devices used by participants in this study, BWH researchers also measured other light-emitting e-readers, laptops, cell phones, LED monitors, and other electronic devices. All of these devices were found to emit blue light, while the Kindle and similar e-book readers don’t emit light and are more like a printed book.