Association between nitrogen dioxide and incident breast cancer in Alberta’s tomorrow project

Breast cancer is a significant global health concern, with millions of cases diagnosed annually. Risk factors for breast cancer include obesity, physical inactivity, poor diet, and alcohol use. Urbanization introduces exposures such as traffic-related air pollution (TRAP), which may impact breast cancer risk. To assess the impact of TRAP, measured in this study using nitrogen dioxide (NO₂), on the risk of post-menopausal breast cancer we conducted a secondary analysis of baseline and follow-up data from the Alberta Tomorrow Project (ATP) cohort, linked to geographic data at the postal code level from the Canadian Urban Environmental Health Research Consortium (CANUE). Cox proportional hazard regression models were built to assess the association between breast cancer risk and NO₂. Direct acyclic graphs (DAG) were used to identify and select relevant confounders for adjustment. The study included 15,536 post-menopausal women and 523 incident breast cancer cases over 12.6 years of follow-up. The hazard ratio (HR) for the initial model, which included all potential confounders (age, education, number of births, fruits and vegetables consumption, income, physical activity, BMI, and smoking) was 1.01 per 10-ppb increase in NO₂. The adjusted HR for a 10-ppb increase in NO₂ measured at baseline (the year participants completed the health and behaviours survey) was 1.10 (95% CI = 0.90, 1.34). Our study found no significant association between NO₂ exposure and post-menopausal breast cancer risk. The variation in reported hazard ratios (HRs) - ranging from 1.01 to 1.10 - reflects different models adjusting for different variables. Our findings suggest a risk magnitude similar to other studies, yet the lack of significant association may be due to sample size limitations and lower NO₂ levels in Alberta compared to other regions globally.