Association of Residential Greenness Exposure with Depression Incidence in Adults 50 Years of Age and Older: Findings from the Cohort Study on Global AGEing and Adult Health (SAGE) in China.

Background: Depression is a social and public health problem of great concern globally. Identifying and managing the factors influencing depression are crucial for preventing and decreasing the burden of depression.

Objectives: Our objectives are to explore the association between residential greenness and the incidence of depression in an older Chinese population and to calculate the disease burden of depression prevented by greenness exposure.

Methods: This study was the Chinese part of the World Health Organization Study on Global AGEing and Adult Health (WHO SAGE). We collected the data of 8,481 residents $\ge 50$ years of age in China for the period 2007-2018. Average follow-up duration was 7.00 ($\pm 2.51$) years. Each participant was matched to the yearly maximum normalized difference vegetation index (NDVI) at their residential address. Incidence of depression was assessed using the Composite International Diagnostic Interview (CIDI), self-reports of depression, and/or taking depression medication. Association between greenness and depression was examined using the time-dependent Cox regression model with stratified analysis by sex, age, urbanicity, annual family income, region, smoking, drinking, and household cooking fuels. Furthermore, the prevented fraction (PF) and attributable number (AN) of depression prevented by exposure to greenness were estimated.

Results: Residential greenness was negatively associated with depression. Each interquartile range (IQR) increase in NDVI $500\text{-m}$ buffer was associated with a 40% decrease [$\text{hazard ratio\hspace{0.17em}}\left(\text{HR}\right)=0.60$; 95% confidence interval (CI): 0.37, 0.97] in the risk of depression incidence among the total participants. Subgroup analyses showed negative associations in urban residents ($\text{HR}=0.32$; 95% CI: 0.12, 0.86) vs. rural residents, in high-income residents ($\text{HR}=0.28$; 95% CI: 0.11, 0.71) vs. low-income residents, and in southern China ($\text{HR}=0.50$; 95% CI: 0.26, 0.95) vs. northern China. Over 8.0% ($\text{PF}=8.69\%$; 95% CI: 1.38%, 15.40%) and 1,955,199 (95% CI: 310,492; 3,464,909) new cases of depression may be avoided by increasing greenness exposures annually across China.

Discussion: The findings suggest protective effects of residential greenness exposure on depression incidence in the older population, particularly among urban residents, high-income residents, and participants living in southern China. The construction of residential greenness should be included in community planning. https://doi.org/10.1289/EHP13947.