Depressive intensity, duration, and their associations with cognitive decline: a population-based study in Korea

Existing epidemiological studies have ignored the effect of depressive duration on cognitive decline despite the presence of biological cues and understudied the depression-cognition association in Asian countries in the context of increasing cognitive burden worldwide. We aimed to comprehensively characterize the effects of depressive duration and intensity on cognitive decline at the population level. A total of 6406 individuals from the Korean Longitudinal Study of Aging (KLoSA) from 2010 to 2018 were included to generate four datasets with durations of 2, 4, 6, and 8 years. Depressive intensity was categorized as no, mild, and major depression according to the Center for Epidemiological Studies Depression scale (CES-D10), and duration was measured by the span of consecutive interviews. Cognitive function was assessed using the Korean Mini-Mental Status Examination (K-MMSE). Multiple linear regressions and meta-regressions were used to estimate the effects of depressive intensity and duration on global cognition and seven cognitive subdomains. Stratified analyses were performed to explore effect differences between subpopulations of different sexes and ages. The potential bias in the effect of depressive intensity on cognitive decline when ignoring duration was also explored. On average, a 1-year longer duration decreased the global cognitive scores by 0.44 (95% CI 0.36, 0.51) across intensities and major depression decreased the scores by an additional 0.82 (95% CI 0.59, 1.04) points than mild depression across durations. Similar trends held for seven cognitive subdomains except for visual construction. Older adults suffered more cognitive decline from major depression than middle-aged adults did. More severe and longer-duration depression lead to greater cognitive decline. Ignoring depressive duration can lead to an overestimated effect of depressive intensity on cognitive decline. The depressive effects and susceptible populations clarified in our study have important implications for the preservation of cognitive health in Asian region.