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Delayed Sleep in Winter Related to Natural Daylight Exposure among Arctic Day Workers

1
Stress Research Institute, Stockholm University, 106 91 Stockholm, Sweden
2
School of Arts, Science and Humanities, University of São Paulo, São Paulo 03828-000, SP, Brazil
3
Human Chronobiology Laboratory, Department of Physiology, Federal University of Paraná, 81531-980 Curitiba, PR, Brazil
4
Health, Life Cycles and Society Department, School of Public Health, University of São Paulo, 01246-904 São Paulo, SP, Brazil
*
Author to whom correspondence should be addressed.
Clocks & Sleep 2019, 1(1), 105-116; https://doi.org/10.3390/clockssleep1010010
Received: 8 October 2018 / Revised: 26 November 2018 / Accepted: 27 November 2018 / Published: 30 November 2018
(This article belongs to the Section Clocks & Sleep in Human Basic Research)
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Abstract

Natural daylight exposures in arctic regions vary substantially across seasons. Negative consequences have been observed in self-reports of sleep and daytime functions during the winter but have rarely been studied in detail. The focus of the present study set out to investigate sleep seasonality among indoor workers using objective and subjective measures. Sleep seasonality among daytime office workers (n = 32) in Kiruna (Sweden, 67.86° N, 20.23° E) was studied by comparing the same group of workers in a winter and summer week, including work and days off at the weekend, using actigraphs (motion loggers) and subjective ratings of alertness and mood. Actigraph analyses showed delayed sleep onset of 39 min in winter compared to the corresponding summer week (p < 0.0001) and shorter weekly sleep duration by 12 min (p = 0.0154). A delay of mid-sleep was present in winter at workdays (25 min, p < 0.0001) and more strongly delayed during days off (46 min, p < 0.0001). Sleepiness levels were higher in winter compared to summer (p < 0.05). Increased morning light exposure was associated with earlier mid-sleep (p < 0.001), while increased evening light exposure was associated with delay (p < 0.01). This study confirms earlier work that suggests that lack of natural daylight delays the sleep/wake cycle in a group of indoor workers, despite having access to electric lighting. Photic stimuli resulted in a general advanced sleep/wake rhythm during summer and increased alertness levels. View Full-Text
Keywords: actigraph; circadian entrainment; high latitude; human; jetlag; light exposure; season; sleepiness; sleep schedule actigraph; circadian entrainment; high latitude; human; jetlag; light exposure; season; sleepiness; sleep schedule
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Lowden, A.; Lemos, N.A.M.; Gonçalves, B.S.B.; Öztürk, G.; Louzada, F.; Pedrazzoli, M.; Moreno, C.R. Delayed Sleep in Winter Related to Natural Daylight Exposure among Arctic Day Workers. Clocks & Sleep 2019, 1, 105-116.

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