Association Between Multimorbidity and Depression in Older Adults: Evidence From Six Large Longitudinal Cohorts

BACKGROUND: Multimorbidity may increase the risk of depression in older adults, but the global average effect of multimorbidity on depression remains unknown. This research aimed to exclude the regional heterogeneity to quantify the exposure-response association between multimorbidity and depression in older adults worldwide. METHOD: We collected 23,947 participants aged 65 years or above from six large prospective cohorts from developed and developing countries, including Mexico, South Korea, Europe, America, China, and England. Multimorbidity was defined as an individual experiencing two or more chronic conditions simultaneously at baseline. Depression was assessed using the Center for Epidemiologic Studies Depression Scale (CES-D) or the EURO-D scale in each wave. We utilized Stratified Cox proportional hazards models to assess the effects of multimorbidity on depression in each cohort. Meta-analysis was then applied to obtain the average effects across cohorts. RESULTS: Multimorbidity was significantly associated with depression in each cohort and the pooled HR for depression excluding the heterogeneity among six cohorts was 1.30 (95% CI: 1.25-1.37, Z = 10.28, p < 0.001). Compared with participants without any chronic condition, those with 1, 2, and ≥3 chronic conditions had HRs for depression of 1.15 (95% CI: 1.09-1.21, Z = 5.10, p < 0.001), 1.37 (95% CI: 1.29-1.45, Z = 10.00, p < 0.001), and 1.57 (95% CI: 1.45-1.70, Z = 10.9, p < 0.001), respectively. The effects of multimorbidity on depression were more pronounced in males (HR: 1.40 in males vs. 1.25 in females) and participants aged between 65 and 74 years (HR: 1.36 in 65-74 years vs. 1.22 in 75 years and older). CONCLUSION: Older adults with multimorbidity are more likely to suffer depression. Effective strategies should be developed for older adults, including preventing and managing chronic conditions and improving mental health services.