Light-emitting e-readers before bedtime can adversely impact
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