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Professor Ron Grunstein AM

Professor of Sleep Medicine


New research shines light on the health risk of eReaders

Posted: December 25, 2014


Just watching the news after a sudden Christmas day storm in Sydney and the TV is full of ads spruiking the Boxing Day sales tomorrow. Among the specials are 15% off e-readers for those switching over from paper books.

However, the electronics stores, Apple and their competitors may be feeling a little uncomfortable with their fiscal position after the release of a scientific paper from the Harvard sleep group this week, Evening use of light-emitting e-Readers negatively affects sleep, circadian timing, and next-morning alertness

As highlighted in these blog pages before, electronic devices for reading and communication are re-engineering life as we know it. However, as the authors point out, light is the most potent environmental signal that impacts the human circadian clock and may therefore play a role in perpetuating sleep deficiency. The circadian body clock system that regulates so much of our bodily functions including sleep – without proper alignment between the sleep and body clock systems our physiology becomes misaligned and a whole heap of things can go wrong. Light at the wrong time can supress the sleep-triggering hormone, melatonin and shift sleep times. For example, too much light in the evening can result in a delay in sleep and possibly impair alertness the next day. Therefore light emitting e-readers uses in the late evening may have negative effects.


The Harvard researchers randomized research subjects to compare the effects of 4 hours reading before bedtime using a light-emitting e-Reader (in the case an iPad) with reading a printed book by reflected light. They investigated sleep, body clock behaviour, melatonin and alertness before and after sleep at night. Subjects were “crossed over” so they received both interventions.

Key findings were that the e-Reader resulted in impaired melatonin secretion and a shift in melatonin to a later time, longer time to fall asleep and less REM sleep during the night. Interestingly the e-Readers were more alert before bedtime with a more “awake” brain wave pattern but this was reversed in the morning when they were drowsier and took longer to feel fully awake that the paper book readers. Importantly, the e-Readers predominantly release short wave spectrum light which is believed to be more alerting than standard wavelength light.

There are obviously method limitations in this type of research – the 4 hour exposure was not continuous but it is sometimes difficult to control for all factors influencing results. The crossover design is a great strength of the study as subjects were exposed to both conditions and thus extra sources of variation were removed. Research performed in younger subjects would be of great interest because of their light exposure from devices.

These data highlight another example where technology and modern life run into the brick wall of human physiology. Can we modify short wavelength light exposure in some way or attenuate the effects in some other way, even pharmacological with melatonin ?

I doubt whether enthusiasm for e-Readers will drop off in tomorrows’s sales but maybe the latest data will provide some pause for thought for the Apple generation. Start the printing presses again !