Non-linear association between residential greenness and general health among old adults in China

While a plethora of evidence has suggested the existence of salutogenic effects of exposure to residential greenness, including mitigating residents' exposure to environmental stressors (the mitigation effect), relevant evidence of these effects in a Chinese context remains limited and inconsistent. This study explored the association between residential greenness and older adults' self-rated general health (SGH) in China, particularly focusing on the potential non-linear association, using the microdata sample from the Chinese one-percent national population sample survey. We further examined whether the association varied significantly according to neighbourhood urbanicity and individual socio-demographic characteristics, and investigated whether residential greenness can mitigate against the detrimental effects of air pollution, higher temperature, and outdoor light pollution at night on older adults' health. We found that higher residential greenness was positively associated with the odds of reporting good health, and a greenness-SGH inverted U-shaped relationship was observed, with a turning point at an NDVI value of 0.40. The greenness-SGH association was stronger for older adults who resided in urban areas, were female, older (>= 80 years), were single or divorced or widowed, had elementary or secondary school education, and lived in households with a car valued over yen 200,000. We also found that greenness can help mitigate the adverse effects of air pollution and outdoor light pollution at night on older adults' SGH. Our findings suggest that providing green infrastructure in a residential environment can promote older people's health through mitigating the hazards of environmental contaminants in a rapidly urbanizing and developing country.