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Background: Air pollution has been classified as a human carcinogen based largely on epidemiological studies of lung cancer. Recent research suggests that exposure to ambient air pollution increases the risk of breast cancer. Methods: Our aim was to characterize associations between residential exposure to ambient fine particulate matter (PM2.5) and the incidence of breast cancer in a cohort of 89,247 women enrolled in the Canadian National Breast Screening Study between 1980 and 1985. Vital status and incident cancers were determined through record linkage to the national registry data through 2005. Individual-level estimates of exposures to PM2.5 at baseline were derived from satellite observations. Six thousand five hundred three incident breast cancers were identified during follow-up. We classified menopausal status using self-reported information collected at baseline and by attained age (50, 52, and 54 years) as women were followed-up. We computed hazard ratios (HRs) and their 95% confidence intervals (CI) using age as the time axis. Models were adjusted for several individual risk factors, including reproductive history, as well as census-based neighborhood-level characteristics. Results: The median residential concentration of PM2.5 was 9.1 μg/m3. In models adjusted for personal and contextual risk factors, a 10-μg/m3 increase in PM2.5 was associated with an elevated risk of premenopausal (HR = 1.26; 95% CI = 0.99, 1.61) but not postmenopausal breast cancer (HR = 1.01; 95% CI = 0.94, 1.10). The elevated risk of premenopausal breast cancer from PM2.5 was only evident among those randomized to the screening arm of the study. Conclusions: Our findings support the hypothesis that exposure to low concentrations of PM2.5 increase the risk of premenopausal breast cancer.

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BACKGROUND: Living in greener areas of cities was linked to increased physical activity levels, improved mental well-being, and lowered harmful environmental exposures, all of which may affect human health. However, whether living in greener areas may be associated with lower risk of cardiovascular disease incidence, progression, and premature mortality is unclear. OBJECTIVES: We conducted a cohort study to examine the associations between residential green spaces and the incidence of acute myocardial infarction (AMI) and heart failure (HF), post-AMI and HF hospital readmissions, and mortality. METHODS: We simultaneously followed four large population-based cohorts in Ontario, Canada, including the entire adult population, adults free of AMI and HF, and survivors of AMI or HF from 2000 to 2014. We estimated residential exposure to green spaces using satellite-derived observations and ascertained health outcomes using validated disease registries. We estimated the associations using spatial random-effects Cox proportional hazards models. We conducted various sensitivity analyses, including further adjusting for property values and performing exploratory mediation analysis. RESULTS: Each interquartile range increase in residential greenness was associated with a 7% [95% confidence interval (CI): 4%, 9%] decrease in incident AMI and a 6% (95% CI: 4%, 7%) decrease in incident HF. Residential greenness was linked to a ∼ 10% decrease in cardiovascular mortality in both adults free of AMI and HF and the entire adult population. These associations remained consistent in sensitivity analyses and were accentuated among younger adults. Additionally, we estimated that the decreases in AMI and HF incidence associated with residential greenness explained ∼ 53% of the protective association between residential greenness and cardiovascular mortality. Conversely, residential greenness was not associated with any delay in readmission or mortality among AMI and HF patients. CONCLUSIONS: Living in urban areas with more green spaces was associated with improved cardiovascular health in people free of AMI and HF but not among individuals who have already developed these conditions.