Light-emitting e-readers 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.

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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Many U.S. workers are sacrificing sleep for work hours, long commutes

A new study shows that paid work time is the primary waking activity exchanged for sleep and suggests that chronic sleep loss potentially could be prevented by strategies that make work start times more flexible.

Results show that work is the dominant activity exchanged for less sleep across practically all sociodemographic categories. Compared to normal sleepers, short sleepers who reported sleeping 6 hours or less worked 1.55 more hours on weekdays and 1.86 more hours on weekends or holidays, and they started working earlier in the morning and stopped working later at night. The highest odds of being a short sleeper were found among adults working multiple jobs, who were 61 percent more likely than others to report sleeping 6 hours or less on weekdays. Respondents who were unemployed, retired or absent from the labor force also obtained significantly more sleep and were less likely to be short sleepers.

"The evidence that time spent working was the most prominent sleep thief was overwhelming," said lead author Dr. Mathias Basner, assistant professor of sleep and chronobiology in psychiatry at the University of Pennsylvania Perelman School of Medicine in Philadelphia.

Short sleepers also traveled more, started traveling earlier in the morning, and stopped later in the evening than normal sleepers. The travel pattern, with peaks at 7 a.m. and 5 p.m., strongly suggests that the majority of travel time is associated with commuting. According to Basner, the results point to several possible solutions for workers' lack of sleep.

"Potential intervention strategies to decrease the prevalence of chronic sleep loss in the population include greater flexibility in morning work and class start times, reducing the prevalence of multiple jobs, and shortening morning and evening commute times," he said.

Results show that with every hour that work or educational training started later in the morning, sleep time increased by approximately 20 minutes. Respondents slept an average of only 6 hours when starting work before or at 6 a.m. and 7.29 hours when starting work between 9 a.m. and 10 a.m. Self-employed respondents with more flexible work times also obtained significantly more sleep than private sector employees and were 17 percent less likely to be a short sleeper.

Study results are published in the December issue of the journal Sleep.

"Getting at least seven hours of nightly sleep is essential to be at your mental, emotional and physical best for whatever you will pour yourself into, either at work or at home," said American Academy of Sleep Medicine President Dr. Timothy Morgenthaler, who was not involved in the study.

Basner and colleagues Andrea M. Spaeth, PhD, and David F. Dinges, PhD, analyzed responses from 124,517 Americans 15 years and older who completed the American Time Use Survey (ATUS) between 2003 and 2011. The computer-assisted telephone interview, which is sponsored by the U.S. Bureau of Labor Statistics and conducted annually by the U.S. Census Bureau, asks participants how they spent their time between 4 a.m. on the previous day and 4 a.m. on the interview day. Responses were combined into 40 distinct activities that captured 99.1 percent of the 24-hour day. Responses combined into the "sleeping" category included napping, waking up and dreaming.

According to the Centers for Disease Control and Prevention (CDC), 30 percent of employed U.S. adults typically sleep 6 hours or less in a 24-hour period, which represents approximately 40.6 million workers. The American Academy of Sleep Medicine recommends that adults get about 7 to 9 hours of nightly sleep for optimal health, productivity and daytime alertness.

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