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Résumé (français)

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Résumé (anglais)

In an increasingly urbanized world, identifying evidence-based strategies to guide the design and maintenance of healthy cities is an essential public health function. Two pressing urban health concerns are high rates of mental disorders and low levels of social connection. Epidemiological studies indicate that access to natural space – either greenspace, such as parks and street trees, or bluespace, such as oceans and lakes – may strengthen social connections and improve mental health. However, gaps remain regarding effects of specific forms of nature, their impacts on objective measures of mental health, and pathways by which any benefits occur. To address these gaps, this dissertation developed and applied a robust model of the presence, form, accessibility, and quality of greenspace and bluespace across the Vancouver, Canada region. This Natural Space Index (NSI) included more than 50 measures at 100-to-1,600-meter buffers for 60,000-plus six-digit postal codes. Analyses based on residential addresses highlighted the extent to which distinct measures result in different assessments, particularly in comparison with standard metrics of surrounding greenness such as the Normalized Difference Vegetation Index (NDVI). Using data from the Canadian Community Health Survey-Mental Health, the percentage of publicly accessible neighborhood nature within 500m had indirect mental health benefits via increased neighborhood social cohesion: each 1% increase was associated with 3-5% increases in reporting higher levels of social cohesion. In turn, individuals with the highest social cohesion had an 86% decrease in the odds of major depressive disorder, a 91% decrease in negative mental health, and a 2.8-point reduction in psychological distress (on a 0-40 scale). When the same question was approached using data on prescriptions related to mental illness, a 0.1-point increase in 250-meter surrounding greenness was linked to a 2% decrease in total psychotropic prescription dispensation and a 3% decrease in antidepressant prescription dispensation. The presence of ten additional street trees within 100m was associated with a 4% reduction in total psychotropic prescriptions. Although many NSI measures showed no association with mental health outcomes, the indirect and direct effects identified by this thesis support calls for expanding equitable access to natural space as part of a broader healthy-city strategy.