Characterizing the modern light environment and its influence on circadian rhythms

• Type of Material: Article
• Authors: Dennis Khodasevich, Columbia University New York; Susan Tsui, Columbia University New York; Darwin Keung, Columbia University New York; Debra J Skene, University of Surrey; Victoria Revell, University of Surrey; Micaela Martinez, Emory University
• Language: English
• Date: 2021-07-28
• Publisher: The Royal Society
• Publication Version: Final Published Version
• Copyright Statement: © 2021 The Authors.
• License: Creative Commons Attribution 4.0 International
• Final Published Version (URL): http://dx.doi.org/10.1098/rspb.2021.0721
• Title of Journal or Parent Work: Proceedings of the Royal Society B: Biological Sciences
• Volume: 288
• Issue: 1955
• Start Page: 20210721
• End Page: 20210721
• Grant/Funding Information: Our research was funded by a pilot award from the NIEHS p30 Center (grant no. ES009089).; M.E.M. was also supported by the Office of the Director, National Institutes of Health of the National Institutes of Health under award no. DP5OD023100.
• Keywords: built environment; Circadian Rhythm; circadian rhythms; Photoperiod; light at night; seasonal rhythms; Seasons; Humans
• Research Categories: Health Sciences, Public Health; Health Sciences, Epidemiology

Abstract

Humans have largely supplanted natural light cycles with a variety of electric light sources and schedules misaligned with day-night cycles. Circadian disruption has been linked to a number of disease processes, but the extent of circadian disruption among the population is unknown. In this study, we measured light exposure and wrist temperature among residents of an urban area during each of the four seasons, as well as light illuminance in nearby outdoor locations. Daily light exposure was significantly lower for individuals, compared to outdoor light sensors, across all four seasons. There was also little seasonal variation in the realized photoperiod experienced by individuals, with the only significant difference occurring between winter and summer. We tested the hypothesis that differential light exposure impacts circadian phase timing, detected via the wrist temperature rhythm. To determine the influence of light exposure on circadian rhythms, we modelled the impact of morning and night-time light exposure on the timing of the maximum wrist temperature. We found that morning and night-time light exposure had significant but opposing impacts on maximum wrist temperature timing. Our results demonstrate that, within the range of exposure seen in everyday life, night-time light can delay the onset of the maximum wrist temperature, while morning light can lead to earlier onset. Our results demonstrate that humans are minimizing natural seasonal differences in light exposure, and that circadian shifts and disruptions may be a more regular occurrence in the general population than is currently recognized.