17 Aug Daytime Bright Light May Reduce Adverse Sleep Effects of Blue Light At Bedtime
MedicalResearch.com Interview with:
Frida Rångtell PhD Student
Department of Neuroscience, Division of Functional Pharmacology
Uppsala University, Sweden
MedicalResearch.com: What is the background for this study? What are the main findings?
Response: Previous studies have demonstrated that evening use of electronic devices emitting blue light, e.g. tablet computers, increases time to fall asleep, reduces the quality of slow-wave sleep (a sleep stage that has for instance been shown to boost memory consolidation and immune functions), and decreases the time in rapid eye movement sleep (which has been proposed to play a role in emotional regulation and consolidation of emotional memories). One explanation could be the blue light-mediated suppression of the sleep-promoting hormone melatonin. Blue LED Warehouse or bedroom lights have a much lower effect on this because they are not shining straight into the viewer’s eyes, like phone LEDs.
In the current experiment however, after 6.5 hours of constant bright light exposure during the day, there were no effects on sleep or melatonin levels after reading a traditional book versus the same book on a self-luminous tablet for two hours before bedtime. Even though the light from the self-luminous tablet was enriched in blue light. Our null findings may at first glance appear surprising, especially in light of previous epidemiological findings linking the use of electronic devices before bedtime with sleep disturbances.
One plausible explanation for these discrepant results across experiments, in our view, is that bright light exposure during daytime – similar to that employed in the present study (~570 lux over 6.5 hours prior to evening light stimulation) – has previously been shown to attenuate the suppressive properties of evening light exposure on melatonin levels.
Our results could therefore suggest that light exposure during the day, e.g. by means of outdoor activities or light interventions in offices, may help combat sleep disturbances associated with evening blue light stimulation. Finally, it must be borne in mind that reading is generally considered to be a cognitively demanding task. Thus, it could be speculated that evening reading may contribute to greater sleep pressure, which may have hampered our ability to detect differences in sleep between the tablet reading and physical book reading conditions. A recent study involving young children has for instance demonstrated that reading at bedtime is associated with improved sleep, as indicated by longer total nocturnal sleep duration.
MedicalResearch.com: What should readers take away from your report?
Response: Our study demonstrates that the extent by which blue light-emitting tablets interfere with sleep is not as simple as we thought, as the effects of evening blue light stimulation on sleep apparently depend on a variety of factors, including duration and daytime light exposure. The latter is quite interesting, as it suggests that light exposure during the day, e.g. by means of outdoor activities or light interventions in offices, may help combat sleep disturbances associated with evening blue light stimulation.
Finally, even if not examined in our study, it must be kept in mind that the emotional arousal from utilizing electronic devices before snoozing, for instance for the sake of checking your work emails or social network accounts, may have an even greater impact on sleep disturbances than the light emitted from these devices. For the latter, increased daytime light exposure or reduction of blue light emitted from screens in the evening might be useless interventions.
MedicalResearch.com: What recommendations do you have for future research as a result of this study?
Response: Future research on the effects of screen light on sleep should take into account important factors that may modulate how sensitive one is to exposure to screen light in the evening, such as age, seasonal effects, duration and timing of evening exposure, as well as more interventional studies of how daytime light exposure impact the effects of light emitted from electronic devices in the evening.
MedicalResearch.com: Thank you for your contribution to the MedicalResearch.com community.
Frida H. Rångtell, Emelie Ekstrand, Linnea Rapp, Anna Lagermalm, Lisanne Liethof, Marcela Olaya Búcaro, David Lingfors, Jan-Erik Broman, Helgi B. Schiöth, Christian Benedict. Two hours of evening reading on a self-luminous tablet vs. reading a physical book does not alter sleep after daytime bright light exposure. Sleep Medicine, 2016; DOI:10.1016/j.sleep.2016.06.016
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