Urban Green Space and the Risk of Dementia: A Population-Based Cohort Study

Background/Aim: A growing body of epidemiologic evidence has identified urban green space as a potential modifiable factor that can improve human health, especially mental health. However, little is known about whether urban green space exposure is associated with reduced risk of dementia.Methods: Our cohort consisted of ~1.7M adults aged 55 to 85 who were long-term Ontario residents prior to cohort inception in 2001. We restricted to individuals who resided in urban areas, and the cohort was followed until 2013. To quantify green space exposure, we used the Landsat 30m satellite-derived normalized difference vegetation index (NDVI) to represent the amount of green vegetation within 250m of individuals’ homes using annual postal code addresses. Dementia incidence was ascertained using population-based health administrative data with a validated algorithm. Mixed effects Cox proportional hazards models were used to estimate the association between green space and dementia. The models included a variety of individual-level and area-level covariates (e.g., age, sex, SES, comorbidities, and air pollution). We also applied a number of sensitivity and stratified analyses to assess the robustness of our estimates.Results: Over the study period, 219,013 individuals in the cohort were diagnosed with dementia. The fully adjusted hazard ratio per IQR increase in green space was 0.96 (95% CI: 0.95-0.97). We did not observe any heterogeneity in our estimate after stratification by selected characteristics (estimates remained between 0.95-0.97). This estimate also remained consistent in sensitivity analyses of different NDVI buffer distances, SES adjustments, and model structures.Conclusions: Our study suggests that increased exposure to urban green space is associated with a reduced risk of dementia among older adults. To our knowledge, this is the first study to assess the relationship between urban green space and dementia.