Dementia Risk in Type 1 and 2 Diabetes: A Nationwide Population-Based Comparison.

AIMS: Diabetes is increasingly recognised as a major contributor to cognitive decline and dementia, but the risk varies by diabetes type and treatment intensity. We compared the risk of all-cause dementia, Alzheimer's disease (AD) and vascular dementia (VaD) among individuals with and without diabetes. METHODS: This population-based retrospective cohort study analysed data from the Korean National Health Insurance Service (2013-2024). A total of 1 322 651 adults aged ≥ 40 years without prior dementia were included. Participants were classified as non-diabetic, type 2 diabetes (T2DM) with oral hypoglycemic agents (OHAs), T2DM with insulin, or type 1 diabetes (T1DM). Incident dementia was identified using ICD-10 codes and anti-dementia prescriptions. Multivariable Cox proportional hazards models adjusted for demographic, lifestyle and clinical factors estimated adjusted hazard ratios (aHRs) for dementia. RESULTS: Dementia incidence rates per 1000 person-years were 4.3 (non-diabetic), 12.7 (T2DM with OHA), 17.9 (T2DM with insulin) and 21.1 (T1DM). Compared with non-diabetic participants, aHRs for all-cause dementia were 1.29 (95% CI 1.26-1.32) for T2DM with OHA, 2.14 (2.00-2.28) for T2DM with insulin and 2.35 (2.12-2.59) for T1DM. Similar trends were observed for AD and VaD. Dementia risk was highest in individuals with T1DM and insulin-treated T2DM, with no significant difference between these groups. CONCLUSIONS: Diabetes was associated with a higher risk of dementia, particularly among individuals with T1DM and insulin-treated T2DM, suggesting that insulin-requiring diabetes represents a high-risk phenotype for cognitive decline. Proactive cognitive screening and optimised glycemic management, including strategies to reduce glycemic variability such as continuous glucose monitoring, may help mitigate dementia risk in these vulnerable populations.