BACKGROUND: The influence of duration of type 2 diabetes mellitus (T2DM) on the likelihood of developing new-onset dementia in post-stroke population is not well understood. Therefore, we aimed to clarify the relationship between the duration of T2DM and the risk of developing dementia in the post-stroke population. METHODS: Leveraging the Korean National Health Insurance Database, this study included 118,790 individuals with a history of stroke but no previous dementia diagnosis. We classified diabetes status into five categories: normoglycemia, impaired fasting glucose (IFG), newly diagnosed T2DM, and established T2DM with durations of less than 5 years and 5 years or more. The primary endpoint was the incidence of all-cause dementia. RESULTS: Among 118,790 participants (average age 64.26 ± 9.95 years, 48% male), 16.7% developed dementia during an average follow-up of 7.3 ± 2.3 years. Participants with a history of T2DM for less than five years at cohort entry had a 26.7% higher risk of developing all-cause dementia compared to those with normoglycemia. Those with T2DM for five years or longer had a 46.7% increased risk, with an adjusted hazard ratio (aHR) of 1.466 (95% confidence interval [CI], 1.408-1.527). Specifically, the risk of developing Alzheimer's disease (AD) and vascular dementia (VaD) rose by 43.4% and 51.4%, respectively, for individuals with T2DM lasting more than five years (aHR 1.434, 95% CI 1.366-1.505
aHR 1.514, 95% CI 1.365-1.679, respectively). CONCLUSIONS: Our findings demonstrated a significant association between an extended duration of T2DM and an increased risk of developing all-cause dementia, including AD and VaD in post-stroke population. These results emphasize proactive dementia prevention approaches in stroke survivors, particularly those with longstanding T2DM.