Exploring the spatial trade-off effects of green space on older people’s physical inactivity: Evidence from Shanghai

Given that green space patterns and population density often show opposing trends over space, this could lead to trade-off (distance/population decay) relationships. Consequently, this paper utilized the Study on Global Ageing and Adult Health (SAGE) data from Shanghai, China, to investigate whether there is a spatial trade-off in the health effects of green spaces on people’s inactivity. Our findings confirmed the trade-off effects of green spaces in reducing sedentary time, using interaction terms to highlight how the health impacts of green spaces vary across different population densities and may thus lead to inconsistent relationships between green space and health outcomes. Generally, the ability of green spaces to affect sedentary time decreased as population density increases, particularly regarding park proximity and the Normalized Difference Vegetation Index (NDVI). Our research also revealed that the trade-off in health benefits from green spaces was influenced by the type of green space. For instance, park proximity, park area, and NDVI showed trade-off effects, with higher population densities enhancing the impact of NDVI on increasing sedentary time (β = 133.871), despite NDVI itself decreasing with a rise in population density (r = -0.68). Conversely, the Green Vegetation Index (GVI) did not demonstrate such an effect. The unequal spatial distribution and composition of green space may further exacerbate health inequities. Therefore, this paper recommends that future provisioning of green spaces should take into account the local urban spatial structure.