Natural light exposure, sleep and depression among day workers and shiftworkers at arctic and equatorial latitudes.

Elaine Cristina Marqueze,Johanna Garefelt,Claudia Roberta Moreno,Suleima Vasconcelos,Arne Lowden,Debra J Skene,Karen L Gamble

doi:10.1371/journal.pone.0122078

Abstract

ObjectivesThis study aimed to investigate the relationship between individual natural light exposure, sleep need, and depression at two latitudes, one extreme with a few hours of light per day during winter, and the other with equal hours of light and darkness throughout the year.MethodsThis cross-sectional study included a sample of Brazilian workers (Equatorial, n = 488 workers) and a Swedish sample (Arctic, n = 1,273).ResultsThe reported mean total natural light exposure per 4-week cycle differed significantly between the Equatorial and Arctic regions. However, shiftworkers from both sites reported similar hours of natural light exposure. Short light exposure was a predictor for insufficient sleep.ConclusionReduced exposure to natural light appears to increase the perception of obtaining insufficient sleep. Arctic workers were more prone to develop depression than Equatorial workers.

Highlights

Light is the most important time cue for maintaining the 24 h period of circadian rhythms in humans [1]
Short light exposure was a predictor for insufficient sleep
The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript

Summary

Introduction

Light is the most important time cue for maintaining the 24 h period of circadian rhythms in humans [1]. In the case of northern latitudes, for instance, lack of natural light during winter exerts a strong influence on sleep problems and depressive illness [4,5,6,7,8,9]. Reasons for the mixed results may be that depressive mood might be more reactive to the seasonal variation of light exposure than sleep and rest activity patterns [21]. Another explanation is that the relationship between sleep and mood might be bi-directional, i.e. that changes in sleep during winter precede changes in mood, and that mood changes affect certain sleep characteristics, especially sleep quality [10]. It has recently been suggested that people living at extreme latitudes may more openly express a vulnerability to seasonal change, whereas such vulnerability is latent in tropical areas [24]

Objectives

Methods

Conclusion