Hannelore Foerster/Getty Images

Using an iPad to read a book in the hours before bedtime can be bad for overall health and alertness, according to s study.

The findings of the study comparing the biological effects of reading an eBook compared to a printed book are published in the journal PNAS (Proceedings of the National Academy of Sciences).

“We found the body’s natural circadian rhythms were interrupted by the short-wavelength enriched light, otherwise known as blue light, from these electronic devices,” said Anne-Marie Chang, a neuroscientist at Brigham and Women’s Hospital.

“Participants reading an LE (light emitting) eBook took longer to fall asleep and had reduced evening sleepiness, reduced melatonin secretion, later timing of their circadian clock and reduced next-morning alertness than when reading a printed book.”

Previous research has shown that blue light suppresses melatonin, impacts the circadian clock and increase alertness but little was known about the effects of the technology on sleep.

The use of light emitting devices immediately before bedtime is a concern because of the extremely powerful effect that light has on the body’s natural sleep/wake pattern and may play a role in perpetuating sleep deficiency.

During the two-week study, 12 participants read eBooks on an iPad for four hours before bedtime each night for five consecutive nights. This was repeated with printed books.

Those reading on the iPad took longer to fall asleep, were less sleepy in the evening and spent less time in REM (rapid eye movement) sleep.

The iPad readers had reduced secretion of melatonin, a hormone which normally rises in the evening and plays a role in inducing sleepiness.

Those who read from the iPad were less sleepy before bedtime, but sleepier and less alert the following morning after eight hours of sleep.

Although iPads were used in the study, the researchers also measured other eReaders, laptops, cell phones, LED monitors, and other electronic devices, all emitting blue light.

The researchers says the findings are important in the light of recent evidence linking chronic suppression of melatonin secretion by nocturnal light exposure with the increased risk of breast cancer, colorectal cancer and prostate cancer.

Business Insider Emails & Alerts Site highlights each day to your inbox. Email Address Join

Follow Business Insider Australia on Facebook, Twitter, LinkedIn, and Instagram.