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Clinical Trial
. 2015 Jan 27;112(4):1232-7.
doi: 10.1073/pnas.1418490112. Epub 2014 Dec 22.

Evening Use of Light-Emitting eReaders Negatively Affects Sleep, Circadian Timing, and Next-Morning Alertness

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Clinical Trial

Evening Use of Light-Emitting eReaders Negatively Affects Sleep, Circadian Timing, and Next-Morning Alertness

Anne-Marie Chang et al. Proc Natl Acad Sci U S A. .
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Abstract

In the past 50 y, there has been a decline in average sleep duration and quality, with adverse consequences on general health. A representative survey of 1,508 American adults recently revealed that 90% of Americans used some type of electronics at least a few nights per week within 1 h before bedtime. Mounting evidence from countries around the world shows the negative impact of such technology use on sleep. This negative impact on sleep may be due to the short-wavelength-enriched light emitted by these electronic devices, given that artificial-light exposure has been shown experimentally to produce alerting effects, suppress melatonin, and phase-shift the biological clock. A few reports have shown that these devices suppress melatonin levels, but little is known about the effects on circadian phase or the following sleep episode, exposing a substantial gap in our knowledge of how this increasingly popular technology affects sleep. Here we compare the biological effects of reading an electronic book on a light-emitting device (LE-eBook) with reading a printed book in the hours before bedtime. 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. These results demonstrate that evening exposure to an LE-eBook phase-delays the circadian clock, acutely suppresses melatonin, and has important implications for understanding the impact of such technologies on sleep, performance, health, and safety.

Keywords: chronobiology; digital media; electronics; phase-shifting; sleep.

Conflict of interest statement

Conflict of interest statement: Dr. Czeisler has received consulting fees from or served as a paid member of scientific advisory boards for: Boston Celtics; Boston Red Sox; Citgo Inc.; Cleveland Browns; Merck; Novartis; Purdue Pharma LP; Quest Diagnostics, Inc.; Teva Pharmaceuticals Industries Ltd.; Valero Inc.; Vanda Pharmaceuticals, Inc. Dr. Czeisler currently owns an equity interest in Lifetrac, Inc.; Somnus Therapeutics, Inc.; Vanda Pharmaceuticals, Inc., and between October 2012 and October 2013, Apple, Inc. and Microsoft, Inc. Dr. Czeisler received royalties from McGraw Hill, Penguin Press/Houghton Mifflin Harcourt, and Philips Respironics, Inc. and has received grants and research support from Cephalon Inc., National Football League Charities, Philips Respironics, ResMed Foundation, San Francisco Bar Pilots and Sysco. Dr. Czeisler is the incumbent of an endowed professorship provided to Harvard University by Cephalon, Inc. and holds a number of process patents in the field of sleep/circadian rhythms (e.g., photic resetting of the human circadian pacemaker). Since 1985, Dr. Czeisler has also served as an expert witness on various legal cases related to sleep and/or circadian rhythms, including matters involving Bombardier, Inc.; Delta Airlines; FedEx; Greyhound; Michael Jackson's mother and children; Purdue Pharma, L.P.; United Parcel Service and the United States of America.

Figures

Fig. 1.
Fig. 1.
Representative raster plot of the 14-d study protocol. Black bars indicate the 10:00 PM–6:00 AM sleep episode in darkness. Gray bars denote dim room light (∼3 lx of white light in the angle of gaze; Materials and Methods), and white bars denote typical indoor room light (∼90 lx in the angle of gaze). Striped bars show the constant posture (CP) procedures. Reading sessions are marked either by the LE-eBook or the print-book and symbols. Participants were randomized to the order of reading condition. Ambient room light level for all reading sessions was dim (∼3 lx).
Fig. 2.
Fig. 2.
Melatonin suppression (A and B) and phase shifting (C and D) during and after the LE-eBook and print book reading conditions. (A) Average waveforms of melatonin (±SEM) during the fifth night of each reading condition. The black bar denotes the scheduled sleep episode (22:00–06:00). (B) Percent suppression for each condition for each participant (filled symbols) and group average (±SEM; open symbols). (C) Average waveforms of melatonin (±SEM) on the evening/night after each reading condition. (D) Average phase shift of melatonin onset for each condition for each participant (filled symbols) and group average (±SEM; open symbols). The main effect of Condition was significant (P < 0.05, mixed model).
Fig. 3.
Fig. 3.
Sleep and sleepiness/alertness measures during and after the print-book and LE-eBook reading conditions. (A) Mean (±SEM) sleep latency to stage N2 in minutes for each reading condition. *P = 0.009, mixed model. (B) Mean (±SEM) accumulation of REM across 8-h sleep episode for each condition. *P = 0.029. (C) Mean duration (in minutes) of sleep stages N1 (white), N2 (light gray), N3 (dark gray), and REM (patterned), and total sleep time (TST; numbers at top of bar) for each reading condition. *P = 0.029. (D) Mean (±SEM) alertness ratings (circles) during and on the morning after each reading condition with respect to clock hour. Mean delta/theta activity in the waking EEG, power density in the 1.0–7.5 Hz range (squares), that was derived from C3/M2 during the fourth and fifth reading sessions of each condition is also shown. (E) Power density in the waking EEG during the LE-eBook condition (open circles) expressed as a percentage of the printed-book condition (100%; dashed line). Two-way mixed-model ANOVA on log-transformed absolute power densities per 0.5-Hz was significant for condition (P < 0.04). Filled triangles at the bottom indicate EEG frequency bins for which the difference between conditions was significant (P < 0.05, post hoc paired t tests).
Fig. 4.
Fig. 4.
Spectral radiometric profile of the LE-eBook device (gray) and incident light reflected by the printed book (black). The peak irradiance for the LE-eBook eReader is ∼450 nm and for the reflected light is 612 nm.

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