Some screens cause sleep loss and cancer – US study

READING an iPad or a Kindle before bed instead of a printed book can cause sleep deprivation and increase the risk of cancer, scientists have warned.

It disrupts normal sleep patterns and can lead to waking up earlier and drowsiness the following day, a study claims.

The light from the devices suppresses the hormone melatonin, low levels of which have been linked to increased risk of breast, prostate, and bowel cancer, scientists in Boston have warned.

Dr Anne-Marie Chang, who led the study, said the body’s normal rhythms ‘‘were interrupted by the short-wavelength enriched light, otherwise known as blue light, from these electronic devices.

‘‘Participants reading a lightemitting eBook took longer to fall asleep and had reduced evening sleepiness, reduced melatonin secretion, later timing of their circadian clock and reduced nextmorning alertness than when reading a printed book.’’

Dr Chang said the light of e-readers has an ‘‘extremely powerful effect’’ on sleep patterns.

She pointed to the newly identified link between night lights and cancer to stress the importance of the findings.

‘‘The results of this study are of particular concern, given recent evidence linking chronic suppression of melatonin secretion by nocturnal light exposure with the increased risk of breast, colorectal, and advanced prostate cancer associated with night-shift work,’’ she said.

The study used iPads but Kindles, laptops and mobile phones were also monitored.

The UK’s eBook market has grown steadily and was worth £300 million (NZ$607m) last year.

Dr Charles Czeisler, head of the Sleep and Circadian Disorders unit at Brigham and Women’s Hospital, where the study was carried out, said sleep length and quality has been declining for 50 years, especially among children and adolescents.