Outdoor light at night at residences and breast cancer risk in Canada

Experimental and epidemiologic studies suggest that light at night (LAN) exposure disrupts circadian rhythm, and this disruption may increase breast cancer risk. We investigated the potential association between residential outdoor LAN and breast cancer risk. A population-based case–control study wa...

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Bibliographic Details
Published in:European journal of epidemiology 2020-06, Vol.35 (6), p.579-589
Main Authors: Ritonja, Jennifer, McIsaac, Michael A., Sanders, Eric, Kyba, Christopher C. M., Grundy, Anne, Cordina-Duverger, Emilie, Spinelli, John J., Aronson, Kristan J.
Format: Article
Language:English
Subjects:
Breast cancer
Cancer
Cardiology
Circadian rhythms
Epidemiology
Health risk assessment
Health risks
Infectious Diseases
Medicine
Medicine & Public Health
Menopause
Night shifts
Oncology
Population studies
Public Health
Regression analysis
Risk management
Shift work
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Summary:Experimental and epidemiologic studies suggest that light at night (LAN) exposure disrupts circadian rhythm, and this disruption may increase breast cancer risk. We investigated the potential association between residential outdoor LAN and breast cancer risk. A population-based case–control study was conducted in Vancouver, British Columbia and Kingston, Ontario, Canada with incident breast cancer cases, and controls frequency matched by age in the same region. This analysis was restricted to 844 cases and 905 controls who provided lifetime residential histories. Using time-weighted average duration at each home 5–20 years prior to study entry, two measures of cumulative average outdoor LAN were calculated using two satellite data sources. Logistic regression was used to estimate the relationship between outdoor LAN and breast cancer risk, considering interactions for menopausal status and night shift work. We found no association between residential outdoor LAN and breast cancer for either measure of LAN [OR comparing highest vs. lowest tertile (DNB) = 0.95, 95% CI 0.70–1.27]. We also found no association when considering interactions for menopausal status and past/current night work status. These findings were robust to changes to years of residential data considered, residential mobility, and longer exposure windows. Our findings are consistent with studies reporting that outdoor LAN has a small effect or no effect on breast cancer risk.
ISSN:0393-2990
1573-7284
DOI:10.1007/s10654-020-00610-x