Show me the money! Associations between tree canopy and hospital costs in cities for cardiovascular disease events in a longitudinal cohort study of 110,134 participants

Health benefits from urban greening are assumed to translate into reduced healthcare expenditure, yet few studies have tested this. At total of 110, 134 participants in the Sax Institute's 45 and Up Study in the Australian cities of Sydney, Newcastle, or Wollongong were linked with hospital cost data for cardiovascular disease (CVD) events up to 30 June 2018. Associations between percentages of total green space, tree canopy, and open grass within 1. 6 km and annual per person CVD-related hospital costs were analysed using generalised linear model (GLM) with gamma density as a component of a two-part mixture model, adjusting for confounders. Overall, 26, 243 participants experienced a CVD-related hospitalisation. Incidence was lower with 10 % more tree canopy (OR 0. 98, 95 %CI 0. 96, 0. 99), but not with higher total green space or open grass. Total costs of hospitalisations per year were lower with 10 % more tree canopy (means ratio 0. 96, 95 %CI 0. 95, 0. 98), but also higher with 10 % more open grass (means ratio 1. 04, 95 %CI 1. 02, 1. 06). It was estimated that raising tree canopy cover to 30 % or more for individuals with currently less than 10 % could lead to a within-sample annual saving per person of AU 193 overall and AU 569 for those who experienced one or more CVD-related hospital admissions. This projects to an estimated annual health sector cost reduction of AU 193 million per 1, 000, 000 individuals for whom tree canopy rose from < 10 % to at least 30 %. In conclusion, this longitudinal study is among the first to analyse actual healthcare cost data in relation to green space in cities. Key findings indicate the lower burden of CVD and fewer associated hospitalisations stemming from upstream investments in protecting and restoring tree canopy in cities translates into substantial reduced costs for the health sector.