Electronics are revolutionizing nearly every aspect of our lives in the 21st century, even the way we read — but is it healthy? Kindles, e-books, and tablet readers have converted many old-fashioned book readers to a plugged-in page turner. Researchers from Harvard Medical School compared reading a classic paper book to light-emitting e-readers right before bed, and published their findings in the Proceedings of the National Academy of the Sciences.

"The light emitted by most e-readers is shining directly into the eyes of the reader, whereas from a printed book or the original Kindle, the reader is only exposed to reflected light from the pages of the book," the study’s lead researcher Charles Czeisler, told the BBC. "Sleep deficiency has been shown to increase the risk of cardiovascular disease, metabolic diseases like obesity and diabetes, and cancer. Thus, the melatonin suppression that we saw in this study among participants when they were reading from the light-emitting e-reader concerns us."

Researchers locked 12 people into a sleep laboratory for two weeks to study their sleeping patterns with each type of bedtime reading approach. After they spent five days reading from a paperback book, they switched to reading from an iPad for the next five days. Their blood was drawn after each test and revealed the sleep hormone melatonin was reduced after participants read an e-book. It also took them longer to fall asleep, and they were found to be more tired the next morning. The original Kindle readers that don’t emit light are safe and similar to reading an old-fashioned book.

It makes sense if we look into the brain for answers. Melatonin is produced in the center of the brain, and accumulates throughout the day. When the lights shut off, the optic nerve sends signals back into the hypothalamus and melatonin is signaled to flood the brain to cue it for bed. The hypothalamus maintains hunger, sleep, body temperature, wakefulness, metabolism, sleep and energy cycles, hydration, and blood pressure regulation among others, according to the Endocrine Awareness Center for Health.

The Electronic Enemy

Living in a 24/7 society can wreak havoc on these carefully constructed hormones and brain regions Ever since Thomas Edison’s public demonstration of the light bulb in 1879, we’ve ignored the sunsets, invaded the night, and occupied the dark. Our bodies are meant to be regulated by internal body clocks that are signaled by the external darkness, but smartphones, tablets, and LED lighting are disrupting the balance. Sleep is increasingly being recognized as the key to a healthy body and mind, but electronics can ruin a perfectly good night’s rest, especially for teens.

Poor sleep hygiene patterns start at a young age, according to the National Sleep Foundation. When the electronics turn off, 53 percent of parents report their teen’s sleep as “excellent.” However, only 27 percent of parents report a level of excellence when they allow their teens to keep devices on at bedtime. Parents are no better. One out of four parents said they read or text and email through electronics, such as e-readers or cellphones at least once a week before bed.

"We should be advising people to minimise their [light-emitting e-reader] use in the evening, particularly teenagers who are a group that are using their phones and tablets late in to the evening," Victoria Revell, who studies how light affects our bodies at the University of Surrey, told the BBC. "People who already have a delayed body clock are delaying themselves much further and that is a very important message."

Source: Czeisler C. Proceedings of the National Academy of the Sciences. 2014.