Objective: To determine whether less severe depression spectrum diagnoses such as dysthymia, as well as depression, are associated with risk of developing dementia and mortality in a "real-world" setting.
Design: Retrospective cohort study conducted using the Department of Veterans Affairs (VA) National Patient Care Database (1997-2007).
Setting: VA medical centers in the United States.
Participants: A total of 281,540 veterans aged 55 years and older without dementia at study baseline (1997-2000).
Measurements: Depression status and incident dementia were ascertained from International Classification of Diseases, Ninth Revision codes during study baseline (1997-2000) and follow-up (2001-2007), respectively. Mortality was ascertained by time of death dates in the VA Vital Status File.
Results: Ten percent of veterans had baseline diagnosis of depression and nearly 1% had dysthymia. The unadjusted incidence of dementia was 11.2% in veterans with depression, 10.2% with dysthymia and 6.4% with neither. After adjusting for demographics and comorbidities, patients diagnosed with dysthymia or depression were twice as likely to develop incident dementia compared with those with no dysthymia/depression (adjusted dysthymia hazard ratio [HR]: 1.96, 95% confidence interval [CI]: 1.71-2.25; and depression HR: 2.18, 95% CI: 2.08-2.28). Dysthymia and depression also were associated with increased risk of death (31.6% dysthymia and 32.9% depression versus 28.5% neither; adjusted dysthymia HR: 1.41, 95% CI: 1.31-1.53; and depression HR: 1.47, 95% CI: 1.43-1.51).
Conclusions: Findings suggest that older adults with dysthymia or depression need to be monitored closely for adverse outcomes. Future studies should determine whether treatment of depression spectrum disorders may reduce risk of these outcomes.