How residential green space exposure reshapes nonlinear relationships between physical activity and sleep quality in aging population:A case study in Nanjing, China

Abstract

Prior studies have identified associations between physical activity (PA) and sleep quality, yet the role of green space exposure in moderating this relationship among older adults remains underexplored. This study investigates the relationships between residential green space, PA, and sleep quality among older adults in Nanjing, China. Residential green space exposure was characterized using four metrics: 2D satellite-derived NDVI (Normalized Difference Vegetation Index), 2.5D street view-based green view index, 3D point cloud-based vegetation ratio, and distance-based proximity to parks. PA levels were assessed using the Godin–Shephard Leisure-Time Physical Activity Questionnaire (GSLTPAQ). Sleep quality was measured using the Pittsburgh Sleep Quality Index (PSQI), where lower scores indicate better sleep quality. Polynomial regression, two-stage least squares regression, and multivariate logistic regression were employed to evaluate nonlinear associations, with interaction analyses testing the moderating effects of green space metrics. The results revealed a nonlinear (inverse U-shaped) association between PA score and sleep quality. Specifically, moderate PA was associated with improved sleep outcomes, whereas high-intensity PA correlated with diminished sleep quality. Residential greenness (i.e., NDVI) moderated this relationship, with higher NDVI values corresponding to attenuated negative correlations between high-intensity PA and sleep quality. These findings underscore the potential role of residential green spaces in reshaping sleep-related outcomes for older adults, offering insights to inform urban planning and public health strategies aimed at fostering supportive environments for aging populations.