Environmental greenspace, subjective well-being, and all-cause mortality in elderly Chinese: Association and mediation study in a prospective cohort.

Background: Subjective well-being (SWB) measures mental health and happiness. Greenspace can have a positive impact on mental health, and higher SWB is associated with lower all-cause mortality. We conducted a mediation analysis on greenspace and all-cause mortality through improving SWB, in a prospective cohort of Chinese older adults.

Methods: We included older adults over 65 from the 2008-2014 Chinese Longitudinal Healthy Longevity Survey (CLHLS). We used satellite-derived normalized difference vegetation index (NDVI) to measure greenspaces and calculated SWB measured by eight items. Three main statistical approaches were used. First, we used generalized estimating equations (GEE) and Cox proportional hazard models to examine NDVI-SWB and SWB-mortality relationships. Second, we conducted a causal mediation analysis to investigate the mediating effect of greenspace on all-cause mortality through SWB. Third, we conducted subgroup analyses to discover effect modification.

Findings: Among 13,133 participants, the mean SWB score and NDVI in 2008 were 28·9 (SD 4·34) and 0·41 (SD 0·14), respectively. We found SWB partially mediated the relationship between residential greenspace and mortality in the adjusted model (average causal mediation effect = 0·11, p = 0·04; average direct effect = 1·96, p < 0·001; total effect = 2·07, p < 0·001) with varying proportions in subgroups. The protective influence was more evident for people with impaired cognitive function, living in rural areas and towns, and with lower income.

Interpretation: We found a positive association between greenspace, SWB, and mortality. Greenness in the living environment confers better mental health and promotes longevity in the elderly population.