Outdoor light at night and breast cancer incidence in the Danish Nurse Cohort

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  • Rebecca B. Clarke, University of Copenhagen
  • ,
  • Heresh Amini, University of Copenhagen, Harvard University
  • ,
  • Peter James, Harvard University
  • ,
  • My von Euler-Chelpin, University of Copenhagen
  • ,
  • Jeanette T. Jørgensen, University of Copenhagen
  • ,
  • Amar Mehta, University of Copenhagen, Statistics Denmark
  • ,
  • Tom Cole-Hunter, University of Copenhagen, University of Sydney, Queensland University of Technology
  • ,
  • Rudi Westendorp, University of Copenhagen
  • ,
  • Laust H. Mortensen, University of Copenhagen, Statistics Denmark
  • ,
  • Steffen Loft, University of Copenhagen
  • ,
  • Jørgen Brandt
  • Ole Hertel
  • Matthias Ketzel
  • Claus Backalarz, DELTA Danish Electronics, Light & Acoustics
  • ,
  • Zorana J. Andersen, University of Copenhagen
  • ,
  • Youn Hee Lim, University of Copenhagen, Seoul National University

Background: Knowledge of the role of melatonin, xenograft experiments, and epidemiological studies suggests that exposure to light at night (LAN) may disturb circadian rhythms, possibly increasing the risk of developing breast cancer. Objectives: We examined the association between residential outdoor LAN and the incidence of breast cancer: overall and subtypes classified by estrogen (ER) and progesterone (PR) receptor status. Methods: We used data on 16,941 nurses from the Danish Nurse Cohort who were followed-up from the cohort baseline in 1993 or 1999 through 2012 in the Danish Cancer Registry for breast cancer incidence and the Danish Breast Cancer Cooperative Group for breast cancer ER and PR status. LAN exposure data were obtained from the U.S. Defense Meteorological Satellite Program (DMSP) available for 1996, 1999, 2000, 2003, 2004, 2006, and 2010 in nW/cm2/sr unit, and assigned to the study participants’ residence addresses during the follow-up. Time-varying Cox regression models were used to calculate the hazard ratios (HRs) and 95% confidence intervals (CIs) for the association between LAN and breast cancer, adjusting for individual characteristics, road traffic noise, and air pollution. Results: Of 16,941 nurses, 745 developed breast cancer in total during 320,289 person-years of follow-up. We found no association between exposure to LAN and overall breast cancer. In the fully adjusted models, HRs for the highest (65.8–446.4 nW/cm2/sr) and medium (22.0–65.7 nW/cm2/sr) LAN tertiles were 0.97 (95% CI: 0.77, 1.23) and 1.09 (95% CI: 0.90, 1.31), respectively, compared to the lowest tertile of LAN exposure (0–21.9 nW/cm2/sr). We found a suggestive association between LAN and ER-breast cancer. Conclusion: This large cohort study of Danish female nurses suggests weak evidence of the association between LAN and breast cancer incidence.

Original languageEnglish
Article number110631
JournalEnvironmental Research
Number of pages8
Publication statusPublished - 2021

Bibliographical note

Funding Information:
This work was funded by a grant from the Danish Council for Independent Research ( DFF-4183-00353 ), Region Zealand Fund, and the Novo Nordisk Foundation Challenge Programme ( NNF17OC0027812 ).

Publisher Copyright:
© 2020 Elsevier Inc.

Copyright 2020 Elsevier B.V., All rights reserved.

    Research areas

  • Breast neoplasms, Environmental exposure, Female, Incidence, Lighting, Middle-aged, Prospective studies, Risk factors

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