Using tablets and backlit e-readers at night can lead to sleep deficiency and damage health, an academic study has claimed.
According to findings published in the US journal Proceedings of the National Academy of Sciences, blue light, the wavelength common in smartphones, tablets and LED lighting, is able to disrupt the body clock and slow or prevent the production of the sleep hormone melatonin.
The use of light-emitting electronic devices for reading, communication, and entertainment has greatly increased recently and the study found that the use of these devices before bedtime prolongs the time it takes to fall asleep, delays the circadian clock, suppresses levels of the sleep-promoting hormone melatonin, reduces the amount and delays the timing of REM sleep, and reduces alertness the following morning.
Of 12 people locked in a sleep laboratory for two weeks, researchers found melatonin was reduced by reading an e-book, and readers took longer to fall asleep, had less deep sleep and were more tired the next morning in comparison to when they read a printed book. The results were concluded after participants spent five days reading from a paperback and five days from an iPad.
Regular blood samples showed the production of the sleep hormone melatonin was reduced by reading an e-book.
Readers also took longer to fall asleep, had less deep sleep and were more tired the next morning.
Lead researcher Prof Charles Czeisler told the BBC News website: "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."
"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."