A lesson for us all – disruption of sleep cycles by eBook readers

We are increasingly dependent on technological devices such as iPads and smartphones through every aspect of our lives – those of you who know me know I am somewhat surgically attached to my iPad these days. However we often don’t stop to consider what effects these devices may be having on our health and physiology. A recent paper in PNAS highlights the impact that tablets have on our sleep cycle.

The study involved 12 young adults who were monitored in a controlled environment for 14 days, and were given either a traditional book or an eBook reader for 5 consecutive nights, and then given the alternative device for 5 nights – the order in which they had the two types of books was randomized amongst the participants. The participants had their sleep monitored, and blood tests taken so their hormonal levels could be analysed.

Melatonin levels during a night using either a traditional book or and eBook reader. Note the lack of melatonin peak in the late evening for those using the eBook reader. Modified from PNAS.
Melatonin levels during a night using either a traditional book or and eBook reader. Note the lack of melatonin peak in the late evening for those using the eBook reader (red arrow). Modified from PNAS.

Strikingly, when participants were given the eBook at night they had significantly lower levels of the sleep-inducing hormone melatonin in their bloodstream during the evening than when they were given a traditional book.  Use of the eBook resulted in it taking 10 minutes longer to fall asleep than those reading a normal book, and reduced the amount of REM sleep experienced. Not only was it more difficult for the participants to get to sleep, but they were also less alert the following morning. There was also an effect on the circadian clock – use of the eBook reader resulted in a phase delay of melatonin accumulation (i.e. the peak melatonin level was later in the night). This suggests that the use of eBook readers or other smart devices at bedtime has significant effects on both circadian rhythms and sleep quality.

The study does have its limitations – there is a relatively small sample size, and the study doesn’t control for the effects of wavelength of light vs overall light intensity. However I think it is one that we should all remember in our daily lives as well as in the context of physiology, as we might all sleep better by putting down the technology and reading a good old paperback.

Reference: Evening use of light-emitting eReaders negatively affects sleep, circadian timing, and next-morning alertness. Chang et al (2015) PNAS 112:1232-1237 DOI:10.1073/pnas.1418490112

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