Sleep science has produced considerable evidence showing that exposure to light before bedtime is bad for sleep. This light can come from computers, phones, night-lights, streetlights outside, and other various sources. One unexpected source has become increasingly common; electronic readers. Light emitting eReaders are exceptionally convenient, in that you can store your whole library of books in it. Moreover, you can now surf the web and do other related activities on them. As many people like to read before bed, one must wonder if eReaders affect your sleep. In a recent study, Chang and colleagues (2015) tackled this question.
Before getting to the results of that study, let’s go over some basic sleep physiology. Our body has what is called a circadian clock, which gives us our daily rhythms of arousal and sleep drive. This clock is driven by both biological and environmental factors. Biologically speaking, our propensity for sleep is driven by melatonin. When our internal clock tells us it’s time for bed, it starts to release melatonin, which makes us sleepy and facilitates sleep onset.
Our social environment serves as our external clock, and also plays a vital role. We rely on specific cues that tell our body that it is time for sleep. Light is the most influential of these factors. Light delays the sleep process by its suppressing effects on melatonin. To get the best quality sleep, our internal and external clocks need to be in synch with one another. When this does not happen, it can lead to sleep difficulty.
So how do eReaders affect sleep? Researchers brought in 12 young, healthy adults into a sleep lab, and had them complete two consecutive conditions of a single study (each participant completed both conditions). This is a within-subjects design, which allows us to compare each of the two conditions within the same participant. Doing this really allows researchers to compare the two conditions of a study. In the first condition, participants spent five consecutive nights in the lab, and read an eReader in a dim room about four hours before bedtime. The second condition consisted of five more nights, but they read a hard copy book. Half of the participants completed the eReader condition first, and the other half completed the hard copy first.
They found that when using the eReader before bed, participants had a whole lot of problems. Their melatonin levels were suppressed by more than 50%, delaying their internal clock by about 90 minutes. Using the eReader lead to participants taking 10 minutes longer to fall sleep, and they also spent less time in REM during sleep. Using the eReader also lead to greater self reported pre-sleep arousal and decreased alertness the following morning.
This study shows that eReaders not only delay your propensity for sleep, but it also decreases sleep quality, leading to decreases in daytime arousal. In a previous post I’ve detailed all the poor health effects of insufficient sleep, but this study adds to that. Melatonin is important in more ways than making sleep come easier to us. Melatonin suppression has been associated with increased risk for breast cancer, colorectal cancer, prostate cancer, and a number of sleep disorders. When approaching bedtime, we should consider that various light sources that may be influencing not only our sleep, but also our health.
Chang, A. M., Aeschbach, D., Duffy, J. F., & Czeisler, C. A. (2015). Evening use of light-emitting eReaders negatively affects sleep, circadian timing, and next-morning alertness. Proceedings of the National Academy of Sciences, 112(4), 1232-1237.