Original ArticleReading from an iPad or from a book in bed: the impact on human sleep. A randomized controlled crossover trial
Introduction
In the past few decades we have witnessed a sharp increase in the availability and use of electronic devices such as mobile phones, video game consoles, DVD players, television, audio players, computers, and tablets [1], [2]. Along with this accessibility there has been an increase in media use among young people [3], [4]. According to a study conducted by the Kaiser Family Foundation, children and youths, 8–18 years old, now use media for at least 7.5 h per day [4]. Much of the media consumption time (20%) is spent on mobile devices, such as cell phones, tablets, or hand-held videogame players [4], devices that have become more lightweight and portable making them easier to use, even in bed. Consistent with this, as many as 90–95% of people between the ages of 13 and 64 report the use of some type of electronic media such as television, computer, video game, or cell phone in the hour before bedtime at least once a week [5], [6].
Such use has raised concerns as it may lead to insufficient sleep and sleep loss. Sleep is regulated by an interaction between three main factors: the homeostatic drive for sleep, the endogenous circadian system, and behavior. The homeostatic sleep drive rises progressively with time spent awake and declines during sleep. The classic marker of the homeostatic sleep drive has been slow wave activity in the delta range (1–4 Hz) in the course of non-rapid-eye-movement (NREM) sleep [7]. The circadian system regulates rhythmicity of our physiological functions, among others the sleep–wake rhythm, so that it normally adheres to a 24-h rhythm.
Light has been shown to shift the timing of the circadian clock. The retinal photoresponsive cell population (intrinsically photoresponsive retinal ganglion cells; ipRGC) contains the photopigment melanopsin, which absorbs a narrow band of wavelengths between 446 and 484 nm – ie, detects blue light. In addition to their connections to our circadian clock, ipRGC cells also project to waking and alerting active areas including the limbic system, striatum, and brainstem [8].
Many screens of electronic devices emit light where short blue wavelengths predominate compared to other light sources with the potential to elicit direct effect on human alertness, sleepiness, and circadian rhythmicity [9], [10]. Epidemiological studies have shown associations between the use of electronic media just before bedtime and delayed bedtime [2], [6], [11], [12], shortened sleep duration [12], [13], and increased daytime tiredness [14]. An experimental study showed that bright light exposure with illuminance >6000 lux decreases sleep propensity, but with no effect on sleep consolidation or REM sleep [15]. In line with this, a recent study showed that adolescents exposed to 3-h evening LED screen illumination (∼105 lux) reported higher sleepiness and had longer reaction times when wearing blue blocking glasses compared to clear lenses [16]. Blue-enriched polychromatic light at relatively low room light levels has further been shown to impact the homeostatic sleep drive by reducing slow wave activity during the first NREM sleep episode [17].
There is a paucity of experimentally and ecologically valid studies on the effects of electronic media just before bedtime and its effect on sleep. One recent study reported that reading from an electronic book for 4 h in the evening delayed sleep onset, reduced evening sleepiness, and delayed timing of the circadian clock (measured by melatonin) compared to reading from a printed book [18].
Still, more studies are needed, especially with more naturally occurring electronic media exposure times. Against this backdrop we conducted a randomized controlled trial investigating the effect on sleep of reading a story (for about 30 min) in bed just before turning out the lights from an iPad compared to reading a story (for about 30 min) from a book in bed. We examined subjective measures of sleepiness before turning the lights out, polysomnographic recordings of sleep, and self-reported sleep onset latency the following morning. We explored whether the two conditions (book vs iPad) would lead to different whole night polysomnographic recordings (time in different sleep stages, total sleep time, nocturnal awakenings). In terms of specific hypotheses we expected reading from an iPad would result in (1) higher evening subjective alertness and (2) longer subjective and objective sleep onset latency. Moreover, we hypothesized that the dynamics of EEG the first 3 h after sleep onset would differ in the two reading conditions: (1) slow waves, indicators of sleep homeostasis, would be reduced and (2) theta and alpha activity would be higher in the iPad condition compared to the book condition during the first NREM sleep episode.
Section snippets
Ethical considerations
The study was approved by the Regional Committee for Medical and Health Research Ethics, Western Norway (2013/992) and conducted in line with the Declaration of Helsinki of 1964. All participants provided informed written consent to participate in the study.
Participants
Twenty volunteers were recruited to the study. All participants were familiar with tablets, were not extreme chronotypes, and were free from sleep, medical, and psychiatric disorders, as assessed by examination and questionnaires. No one
Sleep duration
There were no differences in bedtime and rise time when participants were reading from an iPad compared to a book (all t < 1.6, all p > 0.14). The average sleep duration was 7.8 h vs 7.7 h in the iPad and book conditions, respectively.
Illumination
The illumination was significantly higher in the iPad condition (58.3 ± 6.9 lux) compared to the book condition (26.7 ± 8.0 lux), p <0.001 (see Table 1).
Subjective sleep
Sleepiness levels were rated higher when reading from a book compared to reading from a tablet (KSS: 7.6 ± 0.3
Discussion
Reading a story for 30 min on a tablet resulted in higher alertness before turning the lights out, a delayed EEG dynamics of slow wave activity, and reduced slow wave activity after sleep onset compared to reading a story from a book. There were no differences in sleep onset latency or time spent in the different sleep stages.
Conclusion
In conclusion, the use of commercially available tablets such as iPads which emit blue-enriched light in bed has a direct impact on sleepiness and EEG characteristics of sleep pressure. Hence, the use of commercially available tablets may have consequences in terms of alertness, circadian physiology, and sleep.
Conflict of interest
None.
The ICMJE Uniform Disclosure Form for Potential Conflicts of Interest associated with this article can be viewed by clicking on the following link: http://dx.doi.org/10.1016/j.sleep.2016.02.006.
Acknowledgement
This research was supported by grants from Faculty of Psychology, University of Bergen.
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