The joint association of depression and cognitive function with severe disability among community-dwelling older adults in Finland, Poland and Spain

Objectives: To explore the joint association of depression and cognitive function with severe disability in nationally-representative samples of community-dwelling adults aged 50 years and older from Finland, Poland and Spain. Design: Cross-sectional. Setting: Community-based. Participants: Population-based sample of 7987 non-institutionalized adults aged 50 and older. Measurements: The outcomewas severe disability, defined as =90th percentile of the 12-itemversion of theWorld Health Organization Disability Assessment Schedule (WHODAS 2.0). Past 12-month DSM-IVmajor depressive disorder was assessed with the depression module of theWHO Composite International Diagnostic Interview (CIDI). A global cognitive function score was obtained through neuropsychological tests. Product terms between depression and cognition were introduced in multivariable logistic regression models to test for interaction. Results: Lower cognitive function and depression were both significantly associated with severe disability in all countries. A significant interaction was only found in Finland where the ORs (95% CIs) of depression for severe disability at the 25th (worse), 50th, and 75th (better) percentiles of cognitive function were 7.26 (4.28- 12.32), 11.1 (6.7-18.38), and 17.56 (9.29-33.2), respectively. Conclusion: People with depression and cognitive decline are likely to benefit from the usual evidence-based treatments to reduce the burden of disability. However, in Finland, those with better cognitive functionmay benefit from more aggressive depression treatment. Future research iswarranted to assesswhether our results may be replicated.