Residential greenspace and COVID-19 morbidity and mortality: A nationwide cohort study in Denmark

Background: Identifying modifiable environmental determinants of health is important for improving the resilience of populations to infectious disease. We examined the association between residential greenspace and COVID-19 morbidity and mortality using a Danish Nationwide Cohort, and estimate the potential health benefits of greening initiatives. Methods: We followed all Danish adults aged 50 or older (N = 2,111,233) using the Danish National COVID-19 Surveillance System for COVID-19 incident infection, hospitalization and mortality, from 1 March 2020 to 26 April 2021. Greenspace was characterized using Normalized Difference Vegetation Index (NDVI) at 300x300m grid-cell level and linked to residential addresses. We used Cox regression to assess the association between greenspace and COVID-19 morbidity and mortality, and applied effect modification analyses to identify the most susceptible groups by sociodemographic status and comorbidity. Following a health impact assessment (HIA), we also estimated the preventable burden of disease attributable to greenspace under different counterfactual scenarios. Results: During an average of 14 months follow-up, 62,880 participants were infected with SARS-CoV-2, of whom 8,759 were hospitalized, and 2,382 died, with COVID-19. We observed a negative association between residential greenspace and COVID-19 morbidity and mortality, with hazard ratios (95 % confidence interval) of 0.98 (0.97, 0.99) for SARS-CoV-2 infection, 0.97 (0.94, 0.99) for COVID-19 hospitalization, and 0.96 (0.91, 1.01) for COVID-19 mortality per interquartile range (0.08 unit) increase in NDVI. Stronger associations were observed in the elderly, those with lower SES, and major chronic diseases than their corresponding groups. Regarding the HIA, we estimated that increasing greenspace around residences up to WHO recommended levels would have prevented 8–14 % of COVID-19 events during the first 14 months, with the largest benefits among those with the lowest income, education, or without employment. Conclusion: Greening initiatives in urban areas could help prevent COVID-19, and likely other infectious disease, with socially disadvantaged groups benefiting most.