Effects of green space exposure on acute respiratory illness in community-dwelling older people: A prospective cohort study

• Increased out-of-home green space exposure was significantly associated with the reduced risk of acute respiratory illness (ARI) in a prospective cohort of community-dwelling older adults in Hong Kong. • The association of green space with ARI was more evident for taller shrubs and woodlands than for grassland. • The inverse relationship between green space exposure and ARI incidence was more pronounced in active transportation mode. Few studies have investigated the effects of green space exposure during individuals’ daily activities on respiratory health. This study aims to evaluate how exposure to green space both within residential vicinities and during out-of-home activities influences the incidence of acute respiratory illness (ARI) among older adults. Participants were recruited from a prospective cohort of community-dwelling older people in Hong Kong, who were followed for two years to monitor the occurrence of ARI. Using GPS watches, we tracked participants’ movements for seven consecutive days to gather data on their daily paths. The time-weighted spatial averaging method (TWAM) was used to calculate daily exposure to green space, incorporating metrics such as the presence or absence of total green space and its subtypes, the normalized difference vegetation index (NDVI), canopy cover, and plant area index (PAI). Generalized linear mixed-effects models analyzed the association between these exposures and ARI incidence across warm and cool seasons, with restricted cubic spline models examining dose–response relationships. Among the 134 participants (average age 76.2 years, 82.8 % female), after adjusting confounders, significant protective effects against ARI were observed with increased exposure to canopy cover (odds ratio 0.36, 95 % confidence interval 0.14, 0.88) and PAI (odds ratio 0.38, 95 % confidence interval 0.17, 0.84) outside the home. In warm or cool seasons, total green space and its subcategories also had an inverse relationship with ARI, except for grassland. No significant relationships were observed with NDVI. The protective relationship between green space exposure and ARI incidence demonstrated a dose–response pattern, more pronounced in active mode. No residential green space exposures were significantly associated with ARI risk. Increased green space exposure outside the home is associated with a reduced risk of ARI among older adults living in urban areas. These findings highlight the potential health benefits of engaging in outdoor activities within green environments for respiratory health.