Depression and the risk of Alzheimer disease

Background: Several epidemiologic studies have examined depression as a risk factor for Alzheimer disease with conflicting results. Most studies relied on self-reported depression, but the agreement between self-reported depression and clinical diagnosis has been reported to be weak, thereby diluting the association. Methods: A population-based cohort in Odense, Denmark, of 3346 persons age 65-84 years was examined at baseline (1992-1994) and after 2 years (1994-1996) and 5 years (1997-1999). History of depression was collected at baseline as self-report. We used logistic regression models to estimate odds ratios (ORs) and 95% confidence intervals (CIs). Results: Persons with a history of depression had an increased risk of Alzheimer disease both at baseline (OR = 1.7; CI = 1.0-2.7) and at follow up (at 2 years, 1.9 [1.0-3.3] and at 5 years, 1.6 [0.9-2.7]). Conclusions: Depression was associated with an increased risk of Alzheimer disease. The odds ratios were lower than generally reported from follow-up studies and are similar to cross-sectional studies.