If you receive gifts of e-books in your virtual Christmas stocking this year, you might want to avoid reading them before bedtime.
Worldwide research shows that exposure to electronic light in the hour before bedtime can impair sleep and alertness the next day, and may have a long-term impact on health, performance and safety.
The cause may be short-wavelength–enriched light emitted by electronic devices, German and American researchers report in a study published today.
Exposure to the artificial light has been shown to raise alertness, suppress the hormone melatonin, and phase-shift the circadian rhythm, our natural biological clock. Dim light, on the other hand, “is a cue for circadian rhythms, allowing for production of melatonin,” noted the study, in the science journal Proceedings of the National Academy of Sciences.
The results matter, they said, because of links “with the increased risk of breast, colorectal, and advanced prostate cancer associated with night-shift work … classified as a probable carcinogen by the World Health Organization.”
Reading an electronic book, the study said, “is likely to increase the risk of delayed sleep-phase disorder and sleep onset insomnia, especially among individuals living in society who self-select their bedtimes and wake times. Induction of such misalignment of circadian phase is likely to lead to chronic sleep deficiency.”
The study noted a survey of 1,508 American adults showed 90 per cent regularly use electronics in the hour before sleep.
Researchers compared the quality of sleep obtained after study participants used an eReader before bed, with the quality of their sleep after reading a printed book. Electronic readers experienced more “reduced evening drowsiness, took longer to fall asleep, and reported reduced morning wakefulness.”
Reference: Evening use of light-emitting eReaders negatively affects sleep, circadian timing, and next-morning alertness, by Anne-Marie Chang, Daniel Aeschbach, Jeanne F. Duffy, and Charles A. Czeisler, in PNAS http://www.pnas.org/lookup/doi/10.1073/pnas.1418490112