Association between residential green cover and direct healthcare costs in Northern California: An individual level analysis of 5 million persons.

BACKGROUND AND OBJECTIVE

Prior studies have shown higher green cover levels are associated with beneficial health outcomes. We sought to determine if residential green cover was also associated with direct healthcare costs.

METHODS

We linked residential Normalized Difference Vegetation Index (NDVI) satellite data for 5,189,303 members of Kaiser Permanente Northern California (KPNC) to direct individual healthcare costs for 2003-2015. Using generalized linear regression to adjust for confounding, we examined the association between direct healthcare costs and green cover within250, 500, and 1000 meters (m) of an individual's residence. Costs were determined from an internal cost accounting system that captures administrative and patient care costs for each clinical encounter. Sensitivity analyses included adjustments for comorbidity and an alternative measure of green cover, tree canopy.

RESULTS

We observed a significant inverse association between higher levels of residential green cover and lower direct healthcare costs. The relative rate of total cost for the highest compared to the lowest decile of NDVI was 0.92 (95% CI 0.90-0.93) for the 500 m buffer. The association was robust to adjustment from a broad array of confounders, found at each buffer size, and largely driven by hospitalization, and emergency department visits. Individuals in the top decile of residential green cover had adjusted healthcare costs of $374.04 (95% CI $307.31-$439.41) per person per year less than individuals living in the bottom or least green decile. Sensitivity analyses including tree canopy cover as the green space measure yielded similar findings. Analyses that included adjustment for comorbidity were consistent with the hypothesis that green cover reduces healthcare costs by improving health status.

CONCLUSION

Green cover was associated with lower direct healthcare costs, raising the possibility that residential greening can have a significant healthcare cost impact across the population.