Objectives: Subsyndromal depression is prevalent and associated with poor outcomes in late life, but its effect on the risk of dementia has barely been investigated. This study is aimed to investigate the effect of subsyndromal depression on dementia risk in cognitively normal older adults and patients with mild cognitive impairment.
Methods: Data were collected from a nationwide, population-based, prospective cohort study on a randomly sampled Korean elderly population aged 60 years or older, which has been followed every 2 years. Using 6-year follow-up data of 4456 non-demented elderly, the authors examined the risk of dementia associated with late-onset subsyndromal depression using multivariate Cox proportional hazard models. After standardized diagnostic interviews, subsyndromal depression and dementia were diagnosed by the operational diagnostic criteria and Diagnostic and Statistical Manual of Mental Disorders, 4th edition criteria, respectively.
Results: Subsyndromal depression tripled the risk of dementia in non-demented elderly individuals (hazard ratio = 3.02, 95% confidence interval = [1.56, 5.85], p < 0.001). In subgroup analyses, subsyndromal depression was associated with the risk of dementia in cognitively normal participants only (hazard ratio = 4.59, 95% confidence interval = [1.20, 17.54], p = 0.026); chronic/recurrent subsyndromal depression with increasing severity during the follow-up period was associated with the risk of dementia (hazard ratio = 15.34, 95% confidence interval = [4.19, 56.18], p < 0.001).
Conclusion: Late-onset subsyndromal depression is a potential predictor of incident dementia when it is chronic or recurrent with increasing severity in cognitively normal older adults.
Keywords: Subsyndromal depression; dementia; geriatric psychiatry; population-based study.