Variation in depression's impact on dementia risk by age in adults aged ≥75 years

Late-life depression is linked to an increased dementia risk; however, whether this relationship varies with age remains unclear.

We analyzed data from 1,127,331 individuals aged ≥75 years without dementia from the Korean National Health Insurance database who had undergone health screening between 2012 and 2015. Participants were followed up for ≤10 years. Cox proportional hazards and Fine-Gray subdistribution models were used to estimate dementia risk.

Depression was associated with increased dementia risk in both the old-old (75 to 84 years; hazard ratio [HR]: 1.338, 95% confidence interval [CI]: 1.325 to 1.351) and the oldest-old (≥85 years; HR: 1.111, 95% CI: 1.071 to 1.152), with attenuated effects at older ages. Cerebrovascular disease modified this association in the old-old, but no interaction was observed in the oldest-old.

Depression's impact on dementia risk decreases with age. Cerebrovascular diseases may influence depression-associated neurodegenerative pathways, although this interaction diminishes in the oldest-old.

Depression increased dementia risk in adults aged 75 years and older.The strength of the association declined with advancing age.Effect modification by cerebrovascular disease was observed only in the 75 to 84 old group.Findings support age-related decline in depression's impact on dementia risk.