Late-life depression, subjective cognitive decline, and their additive risk in incidence of dementia: A nationwide longitudinal study.

Objective: Late-life depression and subjective cognitive decline (SCD) are significant risk factors for dementia. However, studies with a large sample size are needed to clarify their independent and combined risks for subsequent dementia.

Methods: This nationwide population-based cohort study included all individuals aged 66 years who participated in the National Screening Program between 2009 and 2013 (N = 939,099). Subjects were followed from the day they underwent screening to the diagnosis of dementia, death, or the last follow-up day (December 31, 2017).

Results: Depressive symptom presentation, recent depressive disorder, and SCD independently increased dementia incidence with adjusted hazard ratio (aHR) of 1.286 (95% CI:1.255-1.318), 1.697 (95% CI:1.621-1.776), and 1.748 (95% CI: 689-1.808) respectively. Subjects having both SCD and depression had a higher risk (aHR = 2.466, 95% CI:2.383-2.551) of dementia than having depression (aHR = 1.402, 95% CI:1.364-1.441) or SCD (aHR = 1.748, 95% CI:1.689-1.808) alone.

Conclusions: Depressive symptoms, depressive disorder, and SCD are independent risk factors for dementia. Co-occurring depression and SCD have an additive effect on the risk of dementia; thus, early intervention and close follow up are necessary for patients with co-occurring SCD and depression.