Journal
CLOCKS & SLEEP
Volume 3, Issue 4, Pages 558-580Publisher
MDPI
DOI: 10.3390/clockssleep3040040
Keywords
light exposure; short-wavelength light; blue-light filter; sleepiness; slow wave sleep; slow wave activity; melatonin; cortisol; distal-proximal skin temperature gradient; affective states
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The study investigated the effects of short-wavelength light from smartphones on sleep and circadian rhythms using a full sample of 33 men. The results showed that smartphone reading without a filter reduced slow-wave sleep, cortisol awakening response, and evening melatonin increase, with positive affectivity predicting better subjective sleep quality in the evening.
Previously, we presented our preliminary results (N = 14) investigating the effects of short-wavelength light from a smartphone during the evening on sleep and circadian rhythms (Hohn et al., 2021). Here, we now demonstrate our full sample (N = 33 men), where polysomnography and body temperature were recorded during three experimental nights and subjects read for 90 min on a smartphone with or without a filter or from a book. Cortisol, melatonin and affectivity were assessed before and after sleep. These results confirm our earlier findings, indicating reduced slow-wave-sleep and -activity in the first night quarter after reading on the smartphone without a filter. The same was true for the cortisol-awakening-response. Although subjective sleepiness was not affected, the evening melatonin increase was attenuated in both smartphone conditions. Accordingly, the distal-proximal skin temperature gradient increased less after short-wavelength light exposure than after reading a book. Interestingly, we could unravel within this full dataset that higher positive affectivity in the evening predicted better subjective but not objective sleep quality. Our results show disruptive consequences of short-wavelength light for sleep and circadian rhythmicity with a partially attenuating effect of blue-light filters. Furthermore, affective states influence subjective sleep quality and should be considered, whenever investigating sleep and circadian rhythms.
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