Bedtime e-books 'may damage health'
Book lovers who enjoy relaxing with an e-book before going to sleep could be damaging their health, researchers have warned.
A study on the impacts of reading light-emitting tablets or electronic reading devices in darkness before bedtime found readers took longer to fall asleep, had a lower quality of sleep and were less alert the next morning compared with reading printed books.
Researchers from Harvard Medical School in Boston, USA, said reading digital books could perpetuate sleep deficiency and disrupt circadian rhythms - the body's sleep and wake cycle - both of which can have adverse impacts on performance and health.
The blue light from these devices is known to suppress the production of the sleep-inducing hormone melatonin but researchers said little was known on the impact of the increasingly popular technology on sleep.
The report, published in the Proceedings of the National Academy of Sciences, said: "Overall, we found that the use of portable light-emitting devices immediately before bedtime has biological effects that may perpetuate sleep deficiency and disrupt circadian rhythms, both of which can have adverse impacts on performance, health and safety."
Harvard Medical School said researchers believed the study was particularly important because chronic sleep deprivation has been linked to an increased risk of cancer, including breast cancer and prostate cancers.
Dr Charles Czeisler, professor of sleep medicine at Harvard Medical School, added: "In the past 50 years, there has been a decline in average sleep duration and quality.
"Since more people are choosing electronic devices for reading, communication and entertainment, particularly children and adolescents who already experience significant sleep loss, epidemiological research evaluating the long-term consequences of these devices on health and safety is urgently needed."
A YouGov survey carried out earlier this year found 78% of Britons are exposed to sleep-disruptive blue light from computer, mobile phone and tablet devices before going to bed.
Among 18 to 24-year-olds included in the 2,149 adults questioned, this figure rose to an astonishing 91%.
During the two-week inpatient study 12 participants read digital books on an iPad for four hours before bedtime each night for five consecutive nights and repeated the exercise with printed books.