Relaxing with an e-book before going to sleep could be damaging your 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, 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 popular technology on sleep.
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 who already experience significant sleep loss.
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.