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.
"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.