Investigating the Role of the Accumulation of Depressive Symptoms for the Risk of Dementia

Abstract

AbstractBackgroundDepressive symptoms vary over the life course and may result from a multitude of causes. With consolidating evidence about depressive symptoms as risk factor of dementia, and previous findings suggesting shared biological pathways of depression and dementia, involving e.g., inflammation, it remains unclear if depressive symptoms reflect a causal risk factor, or an early sign of dementia. We sought to explore the role of depressive symptoms accumulation over time regarding dementia incidence in old age.MethodWe applied the functional relevant life course exposure model (fRLM) to the Survey of Health Aging and Retirement in Europe (SHARE). More precisely, we modelled the accumulation of depressive symptoms, measured with the EURO‐D scale, over time utilizing functional regressions. Data from waves 2 (2006) to 8 (2020) of SHARE was used to examine the association of depressive symptoms with incident self‐report physician‐diagnosis of dementia.ResultIn total, 3,717 participants aged 65 to 70 without dementia at baseline (M [SD] age at baseline = 67.42 [1.70] years) with complete data, participation in at least 2 waves prior to dementia diagnosis or 3 waves prior to loss to follow‐up (M [SD] participation = 3.67 [0.88] waves, MD [SD] follow‐up = 8.0 [2.9] years) were included (58.7% female). Higher exposure to depressive symptoms over time was associated to higher dementia incidence (OR [95% CI] = 3.66 [1.84‐5.87]). Moreover, relevance of depressive symptoms for dementia incidence varied across time windows, suggesting differential associations of depressive symptoms to dementia risk as a function of age. Highest relevance of exposure to depressive symptoms was observed for age 72‐75, i.e., close to diagnosis (Median [SD] age at diagnosis = 76 [3.26] years).ConclusionWhile we observed an association of depressive symptoms with dementia risk, our novel approach extends on previous findings suggesting highest relevance, i.e., predictive ability of depressive symptoms close to diagnosis. Given a build‐up of pathological changes relating to dementia starting as early as two decades prior to cognitive impairment and diagnosis, this suggests depressive symptoms not to be a causal risk factor but rather an early sign or accompanying symptom of dementia.