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Evening Exposure to light-emitting electronics can reduce quality of sleep by suppressing the release of melatonin.

At a Glance: A study published in the Proceedings of the National Academy of Science showed that prolonged reading of electronic devices prior to bedtime may significantly suppress or delay release of melatonin, affecting the quality of sleep and lengthening the time to alertness the next day.

Significance: The use of light-emitting electronic devices for reading, communication, and entertainment has greatly increased recently. We found that the use of these devices before bedtime prolongs the time it takes to fall asleep, delays the circadian clock, suppresses levels of the sleep-promoting hormone melatonin, reduces the amount and delays the timing of REM sleep, and reduces alertness the following morning. Use of light-emitting devices immediately before bedtime also increases alertness at that time, which may lead users to delay bedtime at home. 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.

Researchers at Brigham and Women’s Hospital in Boston studied 12 healthy adults who were randomized to read either a light-emitting eBook or a printed book in dim room light. The participants in each group read for 4 hours prior to bedtime for 5 consecutive evenings. At the end of the 5 days, the subjects switched their assignments. Blood samples were taken during the study and evaluated for melatonin levels. The researchers also documented sleep latency, time and efficiency using polysomnography, a diagnostic tool used in sleep studies.

The reading of eBooks before sleep was associated with a longer time needed to fall asleep and less rapid eye movement (REM) in comparison to reading a printed book. Printed book reading resulted in no suppression of melatonin, but eBook readers experienced an average melatonin suppression of over 55%. In addition, compared to the reading of printed books, the onset of melatonin release in response to dim light occurred 1.5 hours later the day following reading of an eBook. Individuals reading the e-Books also reported being more tired and taking longer to become alert the next morning.

Unlike natural light, electronic devices emit a short-wavelength-enriched light that is more concentrated in blue light. These results demonstrate that evening exposure to light-emitting electronics such as eBooks may delay the circadian clock and suppress the release of melatonin, and this may have a negative impact on sleep, performance, health, and safety.

Chang AM et al. Evening use of light-emitting eReaders negatively affects sleep, circadian timing, and next-morning alertness. Proc Natl Acad Sci U S A. 2015 Jan 27;112(4):1232-7.

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