Population-weighted greenspace exposure tied to lower COVID-19 mortality rates: A nationwide dose-response study in the United States

The COVID-19 outbreak has caused enormous deaths and profound social and economic disruption globally. Accumulating evidence suggests exposure to greenspace may reduce the risk of COVID-19 mortality. Greenspace exposure enhances immune functioning, reduces inflammation, and replenishes gut microbiota may protect against the risk of mortality among those with COVID-19. However, previous studies often fail to distinguish the health effect of different types of greenspace, explore the dose-response association and optimal buffer distance, and consider the spatial dynamics of population distribution and geographic locations of greenspace.

This study examined the associations among ratio of different types of greenspaces, population- weighted exposure to different types of greenspaces, and COVID-19 mortality rates using a negative binomial generalized linear mixed effects model across 3,025 counties in the United States, adjusted for socioeconomic, demographic, pre-existing chronic disease, policy and regulation, behavioral, and environmental factors. The population-weighted measure gave proportionally greater weight to greenspace near areas of higher population density.

Exposure to forest and pasture was negatively associated with COVID-19 mortality rates, while developed open space has insignificant or positive associations with mortality rates.Forest outside parkhas the largest effect size across all buffer distances, followed byforest inside park. The optimal exposure buffer distance is 1km forforest outside park, with 1 unit of increase in exposure associated with a 9.9% decrease in mortality rates (95% confidence interval: 6.9% -12.8%). The optimal exposure buffer distance offorest inside parkis 400m, with 1 unit of increase in exposure, associated with a 4.7% decrease in mortality rates (95% confidence interval: 2.4% - 6.9%).

Greenspaces, especially nearby forest, may be effective at lowering the mortality risk of COVID-19 patients. Our findings suggest that policymakers and planners should prioritize forestry within walking distance of residential clusters to mitigate mortality rates during current and future respiratory pandemics.