Research

Background
Sociodemographic inequalities in depression are well established. However, less is known about variation in inequalities across countries. In this study, we describe cross-national variation in sociodemographic inequalities in depression among older adults. Comparing inequalities across countries is an important step towards understanding how the social environment shapes depression risk.

Methods
In this cross-sectional study, we harmonised data from eight large ageing cohort studies from 18 countries. We restricted our study to adults aged 55 years and older, and measured depression using established cut points in shortened Center for Epidemiologic Studies Depression or EURO-D scales. Next, we estimated prevalence ratios for each country by age, marital status, educational attainment, and gender with logistic regression. To compare estimates across countries, we standardised estimates to the mean sociodemographic distribution across our sample.

Findings
Between Jan 1, 2007, and May 31, 2015, 93 590 older adults completed questions related to depressive symptoms. Sociodemographic inequalities in depression varied substantially across countries. Variation was most apparent for age: prevalence ratios (adults aged 75 years or older vs adults aged 55–65 years) ranged from 2·66 (95% CI 2·13–3·20) in Israel to 0·78 (95% CI 0·72–0·84) in the USA. Heterogeneity by other factors was also apparent. Gender prevalence ratios (women vs men) ranged from 1·07 (95% CI 1·01–1·14) in Korea to 1·96 (95% CI 1·55–2·36) in Greece. Educational prevalence ratios (less than secondary education vs some post-secondary education) ranged from 1·01 (95% CI 0·88–1·14) in Japan to 2·34 (95% CI 2·14–2·55) in the USA. Marital status prevalence ratios (divorced or separated vs married) ranged from 1·11 (95% CI 1·01–1·21) in Chile to 2·01 (95% CI 1·73–2·29) in England.

Interpretation
Inequalities in depression among older adults vary substantially across countries, which might be due to country-specific aspects of the social environment. Future research should investigate social inequality determinants of mental health that might inform the design and evaluation of social, economic, and mental health-related policies and interventions to reduce depression.

Funding
US National Institute of Mental Health and Chilean National Commission for Scientific and Technological Research.