A cross-national study of depression in preclinical dementia: A COSMIC collaboration study

IntroductionDepression commonly accompanies Alzheimer's disease, but the nature of this association remains uncertain.MethodsLongitudinal data from the COSMIC consortium were harmonized for eight population-based cohorts from four continents. Incident dementia was diagnosed in 646 participants, with a median follow-up time of 5.6 years to diagnosis. The association between years to dementia diagnosis and successive depressive states was assessed using a mixed effect logistic regression model. A generic inverse variance method was used to group study results, construct forest plots, and generate heterogeneity statistics.ResultsA common trajectory was observed showing an increase in the incidence of depression as the time to dementia diagnosis decreased despite cross-national variability in depression rates.DiscussionThe results support the hypothesis that depression occurring in the preclinical phases of dementia is more likely to be attributable to dementia-related brain changes than environment or reverse causality.