HealthDay News — People who receive a tablet or e-book reader for the holidays might wind up spending some sleepless nights because of their new gadget.

That’s because the light emitted by a tablet like an iPad can disrupt sleep if the device is used in the hours before bedtime, according to a new Harvard study.

People who read before bed using an iPad or similar “e-reader” device felt less sleepy and took longer to fall asleep than when they read a regular printed book, researchers found.

The morning after reading an e-book, people found it harder to wake up and become fully alert than after reading a regular book — even though they got the same amount of sleep.

The bright light from these devices appears to suppress melatonin, a sleep-promoting hormone that normally increases during the evening and reaches its highest levels as you sleep, said lead researcher Anne-Marie Chang. She’s an associate neuroscientist in the Division of Sleep and Circadian Disorders at Harvard’s Brigham and Women’s Hospital in Boston.

“This light has serious consequences on our sleep and on our alertness, not only while we’re using these electronic devices but the following morning as well, even after eight hours of sleep,” Chang said.

The study’s findings were published in the Proceedings of the National Academy of Sciences.

In the study, 12 young adults read for about four hours before bedtime on five consecutive evenings, in a very dimly lit room at the hospital. Half read e-books and the rest read printed books. After that, they spent another five evenings reading at the hospital, only they traded their e-books for printed books and vice versa.

Participants reading an e-book took longer — about 10 minutes longer — to fall asleep than when they read a printed book. They rated themselves as feeling less sleepy. When they did nod off, they spent less time in REM sleep, the phase of sleep associated with dreaming and deep, restorative sleep, the researchers observed.

Blood drawn from the participants revealed that using an e-book reader delayed the natural nightly increase in their melatonin levels by more than an hour and a half, compared to when they read a printed book.

The following day, participants who read an e-book said they woke up feeling sleepier and took longer to fully wake up and become alert, according to the researchers.

A 2014 National Sleep Foundation poll found 89% of adults and 75% of children have at least one electronic device in their bedroom, said Kristen Knutson, an assistant professor of sleep medicine at the University of Chicago and a research fellow with the foundation.

For about 45% of adults and 30% of kids, that device is a tablet or smartphone, the poll found.


Chang A, et al. Evening use of light-emitting eReaders negatively affects sleep, circadian timing, and next-morning alertness. Proc Natl Acad Sci U S A. 2014; doi: 10.1073/pnas.1418490112.