BOSTON, MA – Use of a light-emitting electronicdevice (LE-eBook) in the hours before bedtime canadversely impact overall health, alertness, andthe circadian clock which synchronizes the dailyrhythm of sleep to external environmental timecues, according to researchers at Brigham andWomen’s Hospital (BWH) who compared the biologicaleffects of reading an LE-eBook compared to aprinted book. These findings of the study arepublished in the Proceedings of the NationalAcademy of Sciences on December 22, 2014.
“We found the body’s natural circadian rhythmswere interrupted by the short-wavelength enrichedlight, otherwise known as blue light, from theseelectronic devices,” said Anne-Marie Chang, PhD,corresponding author, and associate neuroscientistin BWH’s Division of Sleep and Circadian Disorders.“Participants reading an LE-eBook took longer tofall asleep and had reduced evening sleepiness,reduced melatonin secretion, later timing of theircircadian clock and reduced next-morning alertnessthan when reading a printed book.”
Previous research has shown that blue lightsuppresses melatonin, impacts the circadian clockand increase alertness, but little was known aboutthe effects of this popular technology on sleep.The use of light emitting devices immediatelybefore bedtime is a concern because of theextremely powerful effect that light has on thebody’s natural sleep/wake pattern, and maythereby play a role in perpetuating sleep deficiency.
During the two-week inpatient study, twelveparticipants read LE-e-Books on an iPad for fourhours before bedtime each night for fiveconsecutive nights. This was repeated with printedbooks. The order was randomized with some readingthe iPad first and others reading the printed bookfirst. Participants reading on the iPad tooklonger to fall asleep, were less sleepy in theevening, and spent less time in REM sleep. TheiPad readers had reduced secretion of melatonin, ahormone which normally rises in the evening andplays a role in inducing sleepiness. Additionally, iPad readers had a delayed circadian rhythm, indicated by melatonin levels, of more than anhour. Participants who read from the iPad wereless sleepy before bedtime, but sleepier and lessalert the following morning after eight hours ofsleep. Although iPads were used in this study,BWH researchers also measured other eReaders, laptops, cell phones, LED monitors, and otherelectronic devices, all emitting blue light.
“In the past 50 years, there has been a decline inaverage sleep duration and quality,” stated CharlesCzeisler, PhD, MD, FRCP, chief, BWH Division ofSleep and Circadian Disorders. “Since morepeople are choosing electronic devices for reading, communication and entertainment, particularlychildren and adolescents who already experiencesignificant sleep loss, epidemiological researchevaluating the long-term consequences of thesedevices on health and safety is urgently needed.”
Researchers emphasize the importance of thesefindings, given recent evidence linking chronicsuppression of melatonin secretion by nocturnallight exposure with the increased risk of breastcancer, colorectal cancer and prostate cancer.
This research was supported by National Institutesof Health (NIH) grant R01HL77453 and in part byNational Center for Research Resources (NCRR)grant UL1RR025758.
Charles A. Czeisler, M.D., Ph.D., was supported in part by NASA NNX10AF47G and the National Space Biomedical Research Institutethrough NASA NCC 9-58.
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