Subgroup disparities in the mediating roles of income and social support between education level and depressive symptoms among Chinese middle-aged and older adults: an analysis based on the China health and retirement longitudinal study

Objectives This study aimed to identify potential subgroups and explore how the mediating effects of income and social support in the relationship between education level and depressive symptoms vary across these groups among middle-aged and older Chinese adults. Design This study used statistical learning techniques to analyse data from the China Health and Retirement Longitudinal Study (CHARLS), adopting a cross-sectional approach.

Setting The study analysed data from the 2011 baseline survey of CHARLS. Depressive symptoms were evaluated based on the Centre for Epidemiologic Studies Depression Scale form.

Education, social support (informal social support, community support and public support), lifestyle choices (smoke, alcohol and social activity), health conditions (hypertension, dyslipidaemia, diabetes, lung disease, heart problem, kidney disease, digestive disease, arthritis, disability, pain and activity limitation), demographic background (urban residence, sex, age, marital status, body mass index and retirement status) were included in the analysis. Participants 8161 adults over the age of 45 were included.

Primary outcome measures The primary outcome measure was the association between educational level and depressive symptoms mediated by income and social support. These associations may vary across subgroups and were measured using a heterogeneous structural equation modelling method with automatic subgroup detection.

Results Three subgroups were identified and their distinct mediation pathways were revealed. Subgroup 1 had lower depressive symptoms, higher income, better community support and more urban residents.

In this subgroup, education was positively associated with income and community support. Higher income and higher community support were associated with fewer depressive symptoms.

Subgroup 2 had more severe depressive symptoms, more rural residents and higher rates of chronic conditions and body pain. In this subgroup, neither the direct nor the indirect effects of education were statistically significant.

Subgroup 3 had the lowest depressive symptom severity, more rural residents and lower income. In this subgroup, education had a direct protective effect and the indirect pathway through community support was also significant.

Conclusions Income and community support mediate education-depression associations with subgroup heterogeneity. Policies enhancing education, income and community resources could mitigate depressive symptoms.

Trial registration number Not applicable (secondary analysis); CHARLS ethical approval: IRB00001052-11015 (Peking University Biomedical Ethics Committee).