One of my favourite parts of the day is when I get to change into my pajamas and bury myself in blankets and a good book. After a long and busy day, I look forward to my quiet time when I can decompress and read about Cheryl Strayed’s long hike or why Gwyneth Paltrow is wrong about everything (review coming soon!). My husband, on the other hand, prefers to spend this time driving racecars on his phone or reading about new gadgets on our iPad. According to new findings from Harvard Medical School and Brigham and Women’s Hospital in Boston, these differences in our bedtime routines could be the reason why I generally sleep much better than my husband.

In a study published in the Proceedings of the National Academy of Sciences, Anne-Marie Chang and her colleagues found that reading on light-emitting eReaders before bed negatively affected sleep by altering levels of melatonin. The researchers recruited 12 participants and randomly assigned them to one of two groups: one group read printed books for four hours before bed every day for five consecutive days while the other group used eReaders. After five days, the participants switched to reading on the other device. This study design allowed researchers to compare sleep-related metrics from the same individual when they were reading a printed book to when they were reading an eReader. The eReaders used in this study were iPads set to maximum brightness.

Melatonin is a hormone that helps to controls your sleep cycles. If your eyes get progressively droopier as the clock ticks towards your 11:00 pm bedtime, that’s because your melatonin levels are rising and telling your body it needs to sleep. When participants read from an iPad, they had lower levels of melatonin and rated themselves as less sleepy an hour before bedtime. The timing of melatonin release was also affected. Melatonin release was delayed by more than one and a half hours when participants used an iPad compared to when they read a printed book, essentially shifting the sleep cycle to a later time.

The researchers found that when participants read from an iPad, it took them, on average, ten minutes longer to fall asleep than when they read from a printed book. Using an iPad also decreased the amount of rapid eye movement (REM) sleep but did not affect the total amount of sleep or the amount of time spent in the other non-REM sleep stages. Not surprisingly, the effects of using an iPad carried over into the next morning. When participants read from an iPad the night before, they were more sleepy and less alert the next morning than when they read a printed book the night before.

The reason behind the iPad-induced sleep changes could be the light that is emitted from them. As it turns out, these light-emitting tablets produce a lot of short-wavelength light, specifically blue light. Earlier studies have shown that exposure to short-wavelength light, causes greater physiological responses than long-wavelength light, even if the short-wavelength light is not as bright.

The researchers also examined other tablet and eReader devices and found that along with the iPads used, the iPad2, iPhone, iPod Touch, Kindle Fire, and Nook Color all emitted blue light. The only device they tested that did not emit blue light was the Kindle eReader, which reflected the ambient lighting in the room. But don’t throw out your tablet or eReader just yet! Depending on what type of device you have, there are ways of lessening the amount of blue light that is emitted, such as reducing the brightness of the screen and installing apps that filter out blue light.

These new findings suggest that prolonged tablet (and likely computer) use at night may be contributing to the sleep deficit many of us experience on a regular basis. So for a good night’s sleep, make a resolution to power off your devices and enjoy some offline time each night. The Twitterverse will still be there in the morning.

Reference:
Chang, A., Aeschbach, D., Duffy, J., & Czeisler, C. (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 DOI: 10.1073/pnas.1418490112