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

Nonlinear Effects of the Neighborhood Environments on Residents’ Mental Health

“…The vast majority of existing studies exploring relationships between neighborhood environments and mental health assume linearity, but nonlinear relationships between environmental factors and human health are possible [ 13 , 14 ]. For example, a little empirical evidence has shown nonlinear associations (e.g., inverted U-shaped associations, curvilinear response associations) between exposure to residential greenness and health outcomes (e.g., mortality, pulmonary disease, and general health) [ 12 , 16 , 41 ].…”

“…Such results have verified that people who live in neighborhoods with lower levels of greenspace exposure may have limited opportunities for contact with greenness, as well as increased risk of exposure to environmental hazards (e.g., air and noise pollution, excessive heat) and insufficient physical activity, thereby resulting in health-constraining effects. Also, a much higher level of greenness nearby was associated with people’s exposure to more deleterious environments (e.g., pesticides, herbicides), which may seriously harm their health outcomes (e.g., asthma, allergy, and poor general health) [ 14 , 42 ]. While earlier research has affirmed the beneficial influence of appropriate greenspace exposure on mental health, such as providing a healing setting for stress alleviation and psychological relaxation, promoting diverse physical activities, and improving environmental quality, much remains to be learned about the complex relationships between greenspace exposure and mental health and how these relationships may vary by population group, as well as how to define and quantify “appropriate greenspace exposure.” In addition, existing evidence argues that the proper density of built environments (e.g., various facilities, public transport stations, and road networks) is positively associated with health status.…”

“…Several recent studies have not only detected nonlinear relationships between environmental factors and health behaviors (e.g., walking) and outcomes, but they have also highlighted potential threshold effects [ 14 , 45 , 46 ]. The threshold effect is a special type of nonlinear relationship, where the change in impact increases or decreases after exceeding a threshold, which is the point or range of an explanatory variable [ 13 , 19 ].…”

“…For instance, a much higher or lower level of environmental exposure may lead to a decline in health status, whereas the appropriate environmental exposure level can have positive effects on individual health [ 11 , 12 ]. Moreover, only a limited number of studies have focused on the threshold effects of environmental exposures (e.g., greenness, PM 2.5 concentrations, noise, and temperature) on health outcomes (e.g., general health, mood), and then identified the exact threshold values and optimal exposure levels of these environmental factors [ 13 , 14 ].…”

“…Overall, accumulating literature describes the beneficial or detrimental effects of neighborhood environments on residents’ mental health. Although some studies have attempted to analyze nonlinear associations between environmental exposures and health behaviors and outcomes, they typically use only one dimension of the environment (e.g., built environment) or one environmental element (e.g., greenness) and focus on individual behaviors (e.g., physical activity, walking, and travel behavior), some diseases, general health level, or satisfaction [ 14 , 15 , 16 , 17 , 18 ]. Relevant explorations of the complicated nonlinear relationships between neighborhood environments and people’s mental health, as well as the importance of various environmental variables that affect mental health, are rather limited.…”