Urban greenspace is hypothesised to protect cardiovascular health via multiple mechanistic pathways. These include the environmental pathway, via which greenspace attenuates harmful pollution levels (e.g., air and noise pollution); and the physiological pathway, via which accessible greenspace is hypothesised to increase physical activity. My PhD thesis explored the impact of greenspace on environmental and physiological pathway-specific exposures.
I developed pathway-specific exposure models and applied them to participants of a large, adult cohort – UK Biobank (n ~500,000). I estimated residential air pollution exposure via a land-use regression model, with surrounding vegetation cover as a predictor variable to assess the environmental pathway. To assess the physiological pathway, I developed a novel ‘green walkability’ index within a street/path network buffer around participants’ residential addresses. To enhance specificity of greenspace exposure, I assessed greenspace cover surrounding addresses using functional attribute data (e.g., public parks versus private gardens). I conducted survival analyses to examine the associations of greenspace cover surrounding residential addresses with cardiovascular and non-injury mortality, adjusting for relevant individual- and area-level confounders. Integration of vegetation cover into a ‘green walkability’ index did not strengthen effect estimates for physical activity participation in UK Biobank participants when compared to a standard index. I examined the interrelationships of greenspace, air pollution, traffic noise and walkability, and showed that ignoring built environment components related to walkability might result in biased greenspace and physical activity effect estimates. In epidemiological analyses, I showed a protective association across quintiles of surrounding greenspace (100 m circular distance buffer) and non-injury mortality, though not cardiovascular mortality. My thesis points to important policy implications of exposure interrelationships. Greenspace exposure might protect against premature mortality in older adults, though indirect mechanisms (e.g., air flow and walkability of street networks) should be considered, alongside greenspace, to ameliorate specific exposures on the environmental and physiological pathways.