Depression and dementia are common in older adults and often co-occur, but it is unclear whether depression is an etiologic risk factor for dementia.
Objective, Design, Setting and Participants
To clarify the timing and etiology of the association, we examined depressive symptoms assessed in mid-life (1964–1973) and late-life (1994–2000) and the risks of dementia, Alzheimer’s disease (AD) and vascular dementia (VaD) (2003–2009) in a retrospective cohort study of 13,535 long-term Kaiser Permanente members. Depressive symptoms were categorized as none, mid-life only, late-life only or both. Cox proportional hazards models (age as time-scale) adjusted for demographics and medical comorbidities were used to examine depressive symptom category and risk of dementia, AD or VaD.
Main Outcome Measure
Any medical record diagnosis of dementia; Neurology clinic diagnosis of AD or VaD.
Subjects had a mean (standard deviation) age of 81 (5) years in 2003; 58% were women and 25% were non-white. Depressive symptoms were present in 14.1% of subjects in mid-life only, 9.2% late-life only, and 4.2% both. Over 6 years, 23.1% were diagnosed with dementia (5.5% AD, 2.3% VaD). The adjusted hazard of dementia was increased by approximately 20% for mid-life depressive symptoms only (Hazard Ratio [95% confidence interval]: 1.19 [1.07, 1.32]), 70% for late-life symptoms only (1.72 [1.54, 1.92]), and 80% for both (1.77 [1.52, 2.06]). When we examined AD and VaD separately, subjects with late-life depressive symptoms only had a two-fold increase in AD risk (2.06 [1.67, 2.55]) whereas subjects with both mid-life and late-life symptoms had more than a three-fold increase in VaD risk (3.51 [2.44, 5.05]).
Depressive symptoms in mid-life or late-life are associated with an increased risk of developing dementia. Depression that begins in late-life may be part of the AD prodrome, while recurrent depression may be etiologically associated with increased risk of VaD.