Light at night exposure and breast cancer risk in England

Abstract

Introduction: There is increasing evidence that light at night (LAN) may be a breast cancer risk factor. Epidemiological studies, including a case-control study in Georgia, USA, using lung cancer controls, have also found LAN exposure to be associated with an increased risk of breast cancer. We conducted a case-control study to establish the association between outdoor LAN exposure and female breast cancer risk in England. Methods: Cancer data were obtained from the Office for National Statistics for the years 2000 to 2012. LAN values were obtained from satellite data and assigned to each case/control’s residential postcode centroid (the geographic centre of a collection of approximately 15 adjacent households) in a GIS. The association between LAN and breast cancer was assessed using logistic regression, adjusted for age, ethnicity, socioeconomic deprivation, and urban/rural status. Results: Our large, national study, including 375,734 breast cancer cases and 131,920 lung cancer controls, did not confirm earlier findings of an association between breast cancer risk and outdoor light at night. After adjusting for age, deprivation, urban/rural status and ethnicity, compared to lung cancer, the risk of breast cancer was lower amongst women exposed to the highest quintile of outdoor LAN versus the lowest quintile (OR=0.81, 95% CI [0.79-0.83]). As lung cancer cases have a very different age and deprivation profile to breast cancer cases, we are currently repeating our analyses using age- and deprivation-matched controls (skin cancer cases, and cardiovascular hospital admissions) to help interpret these findings. Conclusions: Our study using lung cancer controls does not support the hypothesis that outdoor LAN disrupts melatonin production, with associated impacts on breast cancer risk. As light pollution is a modifiable feature of the urban environment further studies are warranted to assess any possible association.