Association Between Residential Greenness and Risk of Stroke by Ecoregions: The REGARDS Study.

Background: Living in areas with more greenness has been associated with beneficial health outcomes. However, few studies have examined associations of greenness with incidence of stroke, and it is unclear how these associations may vary with the type of vegetation and surrounding ecology. This study evaluated associations between greenness and incidence of stroke by the major ecological regions in the United States.

Methods And Results: We assessed the incidence of stroke in 27 369 participants from the REGARDS (Reasons for Geographic and Racial Differences in Stroke) study, a prospective cohort recruited across the contiguous United States. Greenness was estimated by the normalized difference vegetation index and enhanced vegetation index (EVI) at multiple buffers around home addresses. Participants were assigned to ecoregions using their baseline residence. We estimated the association between residential greenness and incidence of stroke using covariate-adjusted Cox proportional hazards models. Models were stratified by ecoregions to assess how associations varied by areas with unique vegetation and ecology. We observed 1581 incident cases of stroke during the study period. In the full study population, there was suggestive evidence of a protective association between greenness and stroke incidence (hazard ratio [HR], 0.989 [95% CI, 0.946-1.033]) for a 0.1 increase in normalized difference vegetation index within 250 m. Similar results were obtained using enhanced vegetation index and larger radii. In our analysis by ecoregions, we found greenness was associated with lower stroke risk in the Eastern Temperate Forests region (HR, 0.946 [95% CI, 0.898-0.997]), but higher risk in the Great Plains (HR, 1.442 [95% CI, 1.124-1.849]) and Mediterranean California regions (HR, 1.327 [95% CI, 1.058-1.664]).

Conclusions: Vegetation may lower the risk of stroke; however, benefits may be limited to certain contexts of the natural environment.