No doubt many people will be getting iPads or other e-readers as Christmas gifts. If you’re among them, congratulations. But if you plan to use them at night, note that they may cause drowsiness.
The following morning, that is.
In a small-scale but carefully controlled study, researchers found that participants who used e-readers in the evening took longer to fall asleep, and were less alert the next morning, than people who read old-fashioned paper books before turning off the lights.
This suggests the use of such devices “has unintended biological consequences that may adversely impact performance, health and safety,” according to a research team led by neuroscientist Anne-Marie Chang of Brigham and Women’s Hospital in Boston. Evidence of their ability to disrupt sleep patterns is detailed in the Proceedings of the National Academy of Sciences.
The study featured 12 young adults (with a mean age of 25) who agreed to live for two weeks in a private hospital room, so they could be closely monitored. For 10 nights, each spent their final four hours before sleep (that is, from 6 to 10 p.m.) reading.
While there was no significant difference in sleep duration, participants who used e-readers experienced significantly less rapid-eye-movement (REM) sleep during the night.
Five of those nights, they read traditional printed books; for the others, they read on iPads. In both cases, the participants were in “very dim room light,” although the e-reader—which was turned up to maximum brightness—provided additional illumination. Blood samples were taken hourly to measure concentrations of melatonin, a hormone that helps regulate sleep cycles.
Researchers also noted how long it took them to fall asleep, and how much time they spent in the various stages of sleep. Participants rated their level of sleepiness or alertness each morning and evening.
The results were, well, eye-opening. After using the light-emitting books, “participants averaged nearly 10 minutes longer to fall asleep than in the print-book condition,” the researchers write. No wonder: The blood samples revealed the e-readers, but not the print books, “suppressed evening levels of melatonin.”
Participants rated themselves as less sleepy an hour before bedtime if they were using e-readers. The following morning, however, those who read on the electronic devices felt sleepier than their print-book counterparts. It also “took them hours longer to fully ‘wake up’ and attain the same level of alertness,” reported by those who had read traditional ink-and-paper volumes.
While there was no significant difference in sleep duration, participants who used e-readers experienced significantly less rapid-eye-movement (REM) sleep during the night. According to the researchers, this is a likely explanation for the aforementioned grogginess.
These results help explain why, in recent decades, “there has been a decline in average sleep duration and quality, with adverse consequences on general health,” Chang and her colleagues write. “Artificial light exposure has been shown experimentally to produce alerting effects (and) suppress melatonin,” results that have been confirmed by this study.
So the issue isn’t that e-readers are uniquely harmful; it’s that people who know better than to keep the television on late at night think nothing of bringing an e-book to bed. This research suggests the negative results are basically the same.
It seems that whether they’re displaying images of words, light-emitting devices make it harder to fall asleep and lower the quality of your sleep, making for potentially miserable mornings.
So if you’re reading this on a tablet at 10 p.m., it may be time to power down and give yourself some quality time luxuriating in dim light before going to sleep. We’ll still be here in the morning.