LIGHT EMITTING E- READ BEFORE BEDTIME CAN ADVERSELY IMPACT SLEEP
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 researchers at Brigham and Women's Hospital (BWH) who compared the
biological effects of reading an LE-eBook compared to a printed book. These
findings of the study are published in the Proceedings of the
National Academy of Sciences on December 22, 2014.
"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.
During the two-week
inpatient study, twelve participants read LE-e-Books on an iPad for four hours
before bedtime each night for five consecutive nights. This was repeated with
printed books. The order was randomized with some reading the iPad first and
others reading the printed book first. Participants reading on the iPad took
longer to fall asleep, were less sleepy in the evening, and spent less time in
REM sleep. The iPad readers had reduced secretion of melatonin, a hormone which
normally rises in the evening and plays a role in inducing sleepiness.
Additionally, iPad readers had a delayed circadian rhythm, indicated by
melatonin levels, of more than an hour. Participants who read from the iPad
were less sleepy before bedtime, but sleepier and less alert the following
morning after eight hours of sleep. Although iPads were used in this study, BWH
researchers also measured other eReaders, laptops, cell phones, LED monitors,
and other electronic devices, all emitting blue light.
"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."
Researchers emphasize
the importance of these findings, given recent evidence linking chronic
suppression of melatonin secretion by nocturnal light exposure with the
increased risk of breast cancer, colorectal cancer and prostate cancer.
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