December 22, 2014
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Science Daily/Brigham and Women's Hospital
Use of a light-emitting electronic device (LE-eBook) in the hours before bedtime can adversely impact overall health, alertness, and the circadian clock which synchronizes the daily rhythm of sleep to external environmental time cues, according to new research that compared the biological effects of reading an LE-eBook compared to a printed book.

"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 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."

Previous research has shown that blue light suppresses melatonin, impacts the circadian clock and increase 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 extremely powerful effect that light has on the body's natural sleep/wake pattern, and may thereby play a role in perpetuating sleep deficiency.

"In the past 50 years, there has been a decline in average sleep duration and quality," stated Charles Czeisler, PhD, MD, FRCP, chief, BWH 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, epidemiological research evaluating the long-term consequences of these devices on health and safety is urgently needed."
http://www.sciencedaily.com/releases/2014/12/141222131348.htm