Evening use of light-emitting eReaders negatively affects sleep, circadian timing, and next-morning alertness

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.

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.

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.

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.

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.