The Association Between Long-term Exposure to Traffic-related Air Pollution and Cardiovascular Mortality in Ontario, Canada

Introduction: Cardiovascular disease is the leading cause of mortality worldwide. There is suggestive evidence that chronic exposure to traffic-related air pollution may increase the incidence and mortality from cardiovascular disease. However, in few studies has the health effects of traffic-related air pollution been examined at the relatively lower concentrations of pollution such as observed in Canadian cities. In addition, the few studies using land use regression models to assess exposures of traffic-related air pollution at fine geographic resolutions have had modest sample sizes, so statistical power was limited. The purpose of this dissertation was to further our understanding of the aetiology of traffic-related air pollution in relation to cardiovascular outcomes through improved estimates of exposure derived through the juxtaposition of accurate information on residential addresses with improved methods of estimates of spatial concentrations of traffic-related air pollution.;Results and Discussion: In the Ontario tax cohort study, I found that for each increase of 5 parts per billion (ppb) of NO 2, the rate ratios for mortality for all cardiovascular disease and for ischemic heart disease, using different models, varied between 1.04 (95%CI: 1.00-1.09) and 1.10 (95%CI: 1.00-1.21). I found no associations between traffic pollution and cerebrovascular mortality (excess rates of mortality of 0.95 (95%CI: 0.89-1.02)). These results support the hypothesis that long-term exposure to traffic-related air pollution increases the mortality of cardiovascular disease.;Methods: To achieve the research objectives of this dissertation, three studies were conducted. First, I conducted a systematic review of epidemiological evidence between 1950 and 2011 regarding the chronic health effects of ambient air pollution. Second, I developed three new methods of estimating historical exposure to traffic-related air pollution at fine geographic scales through extrapolating "current" land use regression models back in time. These three extrapolation methods entailed multiplying the predicted concentrations of NO2, a marker of traffic-related air pollution, by the ratio of past estimates of concentrations from fixed-site monitors, such that they reflected the change in the spatial structure of NO2 from measurements at fixed-site monitors. Third, I conducted a population-based cohort study to determine whether an association exists between traffic-related air pollution and cause-specific cardiovascular mortality among adults living in Ontario, Canada. This population-based cohort study used as a sampling frame the Canadian Federal income tax file and subjects living in Hamilton, Toronto, and Windsor were included in the analyses. I made use of estimates of exposure to traffic-related air pollution using land use regression models and the back extrapolation methods. I carried out adjusted Cox regression models included known individual risk factors and selected ecological covariables and I carried out sensitivity analyses using indirect methods to adjust for smoking that was not available on individuals in the cohort.