E-readers harm sleep quality, study finds
Users of light-emitting devices are less rested than those who stick to traditional books
Your bedtime e-reader habit may be robbing you of sleep rather than helping you drift off, a US study has found.
Light emitted by devices such as the Kindle Fire, Nook Colour and iPad affected the body's release of the sleep hormone melatonin, the study by researchers at Pennsylvania State University found.
"Electronic devices emit light that is short-wavelength-enriched light, which has a higher concentration of blue light," said Anne-Marie Chang, assistant professor of biobehavioural health at Penn State.
"This is different from natural light in composition, having a greater impact on sleep and circadian rhythms," Chang said.
The study, published in the latest edition of the Proceedings of the National Academy of Science, observed the sleep patterns of 12 adults over two weeks to compare their sleep when they read from an iPad to reading a printed book at night.
Researchers found participants took almost 10 minutes longer to fall asleep after reading from light-emitting iPads than they did after reading a conventional book.
Participants also had a lower amount of REM, or rapid eye movement, sleep after reading from iPads.
"Our most surprising finding was that individuals using the e-reader would be more tired and take longer to become alert the next morning," said Chang. "This has real consequences for daytime functioning."
Participants stayed at a Boston hospital for the duration of the study, where their brainwaves, breathing and heart rate were monitored.
Each person read from an iPad for five nights in a row as well as reading for five consecutive nights from a conventional book, for four hours from 6pm to 10pm.
Researchers measured the amount of light emitted from each device and found the iPad was the brightest, compared to the Kindle Fire and Nook Colour, which were the dimmest.
Chang said the effect of such reading devices used at night warranted further study as there may be longer-term health consequences.
Use of e-readers is growing in Hong Kong, according to a survey of 805 visitors to the Hong Kong Book Fair in July. It found 35 per cent of respondents had bought e-books in the past 12 months, a 19 per cent increase from the previous year.
But while they spent an average of HK$478 a year on e-books, the book fair attendees still increased their spending on paper books from the previous year by some HK$130 each, to an average of HK$1,839.
"I am careful to power down before I sleep. Sometimes I feel tired, but there are so many factors - I drink a lot of coffee," said Anne Greenleaf, a Hong Kong-based political science doctoral student and Kindle reader.