Route Study

The main objectives of this project are:

1. To determine how air pollution influences the transition of health states from incidence of major chronic diseases, to their progression, and finally to premature death; and

2. To evaluate the effectiveness of some widely-implemented or potential individual-level and population-level strategies in reducing the harmful effects of air pollution on health in Canada

There is unequivocal evidence that long-term exposure to air pollution, even at the relatively low levels observed in Canada, is responsible for increased incidence and mortality from major chronic diseases. While different health outcomes have been extensively investigated in previous studies, the segregation

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of air pollution research by individual outcome is artificial. Little is known about the impact of air pollution on shaping individuals’ physiological transformations (various disease states, frailty, and death). Even less is known about the effectiveness of past interventions of air pollution and whether other possible measures are needed. Advances in our understanding of specific strategies are of crucial importance for developing and strengthening evidence-based actions to mitigate the health effects of air pollution in Canada. To fill these major gaps in knowledge and policy formation, this research contract will compile the entire adult population in Ontario through data linkage across multiple health administrative databases (e.g., chronic disease databases), health survey data (e.g., Ontario portion of the Canadian Community Health Surveys [CCHS]), and environmental exposure data (e.g., air pollution, noise, greenness). These population-based administrative databases were linked and held at ICES, Toronto, Ontario.

This contract will entail three complementary analyses using the Ontario adult population: 1) a study to quantify path-specific effects involving causally ordered mediators (i.e., incidence of selected major diseases and their readmissions) covering a wide array of scenarios of disease trajectories; 2) a study to examine whether use of common cardiovascular medications may moderate the negative effect of air pollution on cardiovascular morbidity and mortality across Ontario; and 3) a study to examine the extent to which a hypothetical policy to enforce low emission zones in the city of Toronto would yield health benefits.

To quantify the role of air pollution exposure on different scenarios of disease trajectories, the research team will conduct a series of mediation analyses in consultation with the scientific team at Health Canada. For air pollutants, the Contractor will use satellite-based surface concentrations of fine particulate matter (PM2.5), land-use regression model-derived nitrogen dioxide (NO2) concentrations, and fusion-based ozone (O3) concentrations. For covariates, the Contractor will gather information on age, sex, marital status, education, occupation, body mass index (BMI), smoking, alcohol use, consumption of fruits and vegetables, physical activity from CCHS data, comorbidities from provincial health administrative databases, and various neighborhood-level factors (e.g., percentages of immigrants) from Census data. The proportions of the effect of air pollution on mortality that are mediated through the development of the major diseases and their progression will be estimated. Multiple subgroup analysis and sensitivity analyses will also be conducted to test the key assumptions of mediation analysis.

To examine whether cardiovascular medications moderate cardiovascular morbidity and mortality in association with air pollution, the Contracor will conduct a nested case-control study. The outcomes of interest are death and hospitalization from any cardiovascular cause, as well as death and hospitalization from coronary heart disease and stroke (more specific outcomes). The Contractor will use conditional logistic regression models to estimate the impact of air pollution on cardiovascular morbidity and mortality for each air pollutant-cardiovascular outcome combination. Given that medication use may fall in the caual pathways between air pollution and cardiovacular outcomes (thus act as mediators), the Contractor will also apply advanced causal mediation methods following the strategdy developed by a member of the scientific team at Health Canada (Dr. Jay Kaufman, McGill University).

To examine what would be the potential health benefits of implementing hypothetical low emission zones (LEZ) in Toronto, the Contractor will conduct a simulation analysis. This simulation will include three stages that have recently been developed by a member of the scientific team at Health Canada (Dr. Tarik Benmarnia, University of California, San Diego).Realistic estimates from observed changes in air pollution due to a LEZ as described in the literature will be used. As a complementary approach, hypothetical reduction from a no policy scenario, expanding up to an intervention-specific reduction in PM2.5 and NO2 of 10%, will be considered.