Date on Master's Thesis/Doctoral Dissertation

8-2022

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Epidemiology and Population Health

Degree Program

Public Health Sciences with a specialization in Epidemiology, PhD

Committee Chair

Baumgartner, Kathy

Committee Co-Chair (if applicable)

Baumgartner, Richard

Committee Member

Baumgartner, Richard

Committee Member

Bhatnagar, Aruni

Committee Member

Boone, Stephanie

Committee Member

Judd, Suzanne

Author's Keywords

air pollution; greenness; stroke; REGARDS; ecoregion; environment

Abstract

The adverse health effects of air pollution have long been recognized, with the majority of morbidity and mortality due to its effects on the cardiovascular system. Alternatively, living in areas with higher greenness has been found to be beneficial to a wide range of health outcomes. However, few studies have considered that these relationships may vary depending on the surrounding ecosystem. The purpose of this dissertation was to examine the effects of long-term exposure to air pollution and greenness on incidence of stroke, and how these relationships vary with the major ecological regions of the United States. We utilized the Reasons for Geographic and Racial Differences in Stroke study (REGARDS), a prospective cohort study of 30,239 participants recruited between 2003 and 2007. One-year and 3-year exposure to PM2.5, PM10, O3, NO2, SO2, and CO were assigned to participants’ census block group. Residential greenspace was estimated by the Normalized Difference Vegetation Index (NDVI) and Enhance Vegetation Index (EVI). The risk of incident stroke associated with baseline pollutants and greenness was assessed using adjusted Cox proportional hazards models. Models were stratified by EPA created ecoregions to determine how associations varied by geographic areas with similar environmental features. The hazard ratio (95% CI) for a 2.9 µg/m3 (interquartile range) increase in 1-year PM10 was 1.07 (1.003, 1.15) for risk of stroke in the full study population. We did not find evidence of positive associations for PM2.5, O3, NO2, SO2, and CO in the full population. In our ecoregion specific analysis, we found positive associations for PM2.5 in the Great Plains ecoregion, while associations for PM10 were strongest in the Eastern Temperate Forests region. There was suggestive evidence of a negative association between greenness and stroke incidence (hazard ratio: 0.989; 95% CI: 0.946, 1.033) for a 0.1 increase in NDVI within 250-m. In our analysis by ecoregions, we found negative associations between greenness and stroke incidence in the Eastern Temperate Forests region, but positive associations in the Great Plains and Mediterranean California regions. The associations between exposure to air pollution, greenness and stroke incidence varied by ecoregion, highlighting the importance of considering the complexities of the natural environment.

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