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In This Issue:
Charles Czeisler and Anne-Marie Chang
Nighttime readers may want to consider reaching for a traditional book instead of basking in the blue glow of light-emitting electronic devices, such as tablets, some e-readers, smart phones and laptops.
New research from BWH has found that the use of light-emitting electronic devices 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.
Researchers compared the biological effects of reading a light-emitting e-book to a printed book, and their findings were published in the Proceedings of the National Academy of Sciences last month.
"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 than when reading a printed book."
Previous research had shown that blue light suppresses melatonin, impacts the circadian clock and increases alertness, but little was known about the effects of this popular technology on sleep. The use of light-emitting devices immediately before bedtime is a concern because of the powerful effect that light has on the body's natural sleep and wake pattern, and may thereby play a role in perpetuating sleep deficiency.
During the two-week inpatient study, 12 participants read light-emitting e-books on an iPad for four hours before bedtime each night for five consecutive nights. This was repeated with printed books. Each study participant read in both conditions, and the order was randomized; six read on the iPad first and the other six read the printed books first. Participants reading on an iPad took longer to fall asleep and spent less time in REM sleep, often referred to as dream sleep. The iPad readers had reduced secretion of melatonin, a hormone that normally rises in the evening and plays a role in inducing sleepiness.
Additionally, iPad readers had a delayed circadian rhythm, indicated by the timing of melatonin levels, of more than an hour. Participants who read from the iPad were less sleepy before bedtime, but were sleepier and less alert the following morning after eight hours of time in bed.
Although iPads were used in this study, BWH researchers also measured other light-emitting e-readers, laptops, cell phones, LED monitors and other electronic devices, all emitting blue light. The standard Kindle e-reader, which doesn't emit light, was more akin to a printed book.
"In the past 50 years, there has been a decline in average sleep duration and quality," said Charles Czeisler, PhD, MD, FRCP, 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."