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. 2022 Nov:169:107495.
doi: 10.1016/j.envint.2022.107495. Epub 2022 Sep 2.

Light at night and the risk of breast cancer: Findings from the Sister study

Marina R Sweeney  1 , Hazel B Nichols  2 , Rena R Jones  3 , Andrew F Olshan  2 , Alexander P Keil  2 , Lawrence S Engel  2 , Peter James  4 , Chandra L Jackson  5 , Dale P Sandler  6 , Alexandra J White  7
Affiliations

Light at night and the risk of breast cancer: Findings from the Sister study

Marina R Sweeney et al. Environ Int. 2022 Nov.

Abstract

Background: Light at night (LAN) may alter estrogen regulation through circadian disruption. High levels of outdoor LAN may increase breast cancer risk, but studies have largely not considered possible residual confounding from correlated environmental exposures. We evaluated the association between indoor and outdoor LAN and incident breast cancer.

Methods: In 47,145 participants in the prospective Sister Study cohort living in the contiguous U.S., exposure to outdoor LAN was determined using satellite-measured residential data and indoor LAN was self-reported (light/TV on, light from outside the room, nightlight, no light). We used Cox proportional hazards models to calculate hazard ratios (HRs) and 95% confidence intervals (CIs) for the associations between outdoor and indoor LAN and breast cancer risk. Models were adjusted for age, race/ethnicity, educational attainment, annual household income, neighborhood disadvantage, latitude, and population density as a proxy for urbanicity. To evaluate the potential for residual confounding of the outdoor LAN and breast cancer relationship by factors associated with urbanicity, we considered further adjustment for exposures correlated with outdoor LAN including NO2 [Spearman correlation coefficient, rho (ρ) = 0.78], PM2.5 (ρ = 0.36), green space (ρ = - 0.41), and noise (ρ = 0.81).

Results: During 11 years of follow-up, 3,734 breast cancer cases were identified. Outdoor LAN was modestly, but non-monotonically, associated with a higher risk of breast cancer (Quintile 4 vs 1: HR = 1.10, 95% CI: 0.99-1.22; Quintile 5 vs 1: HR = 1.04, 95% CI: 0.93-1.16); however, no association was evident after adjustment for correlated ambient exposures (Quintile 4 vs 1: HR = 0.99, 95% CI: 0.86-1.14; Quintile 5 vs 1: HR = 0.89, 95% CI: 0.74-1.06). Compared to those with no indoor LAN exposure, sleeping with a light or TV on was associated with a HR = 1.09 (95% CI: 0.97-1.23) in the adjusted model.

Conclusions: Outdoor LAN does not appear to increase the risk of breast cancer after adjustment for correlated environmental exposures.

Keywords: Breast cancer; Environmental epidemiology; Light at night; Prospective cohort.

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Conflict of interest statement

Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Figures

Figure 1.
Figure 1.
Outdoor light at night for 2006, as captured by the U.S. Defense Meteorological Satellite Program. Blue dots represent Sister Study participants’ primary enrollment residences.
See this image and copyright information in PMC

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