BackgroundThis study aimed to assess the effect of informal social support (ISS) on the health of Chinese older adults, identify channels of the association between the two, and assess the magnitude of this effect in different groups of older adults.MethodsBased on the data from the 2018 China Longitudinal Aging Social Survey (CLASS), we first used both the Quality of Well-Being (QWB) scale and the analytic hierarchy process (AHP) method to construct the QWB score that can objectively measure the health status of Chinese older adults. Next, we conducted an econometric equation controlling for various high-dimensional fixed effects, estimated the effects using the Tobit model, and used various robustness check strategies and the propensity score matching (PSM) method to ensure reliability and deal with the potential endogeneity, respectively. Finally, we performed staging and grouping regression for mechanism and heterogeneity analysis.ResultsThe mean QWB score of Chinese older adults was 0.778. ISS has a significant positive effect on the health of older adults (P< 0.001), and there were similar patterns of findings for the effects of SE (P< 0.001), PSS (P< 0.001), and ES (P< 0.001). Additionally, the health promotion effect is higher in older adults who are male (P< 0.001), under the age of 80 (P< 0.001), with agricultural household registration (P< 0.001), or with high income (P< 0.001) than in the control group.ConclusionISS, including SE, PSS, and ES, had significant promotion effects on the health of older adults, especially on those who are male, under the age of 80, with agricultural household registration, or with high income. Meanwhile, these effects could be reflected through two channels: alleviating loneliness and improving the positive emotional status of older adults.