Association between Age at Diagnosis of Type 2 Diabetes and Subsequent Risk of Dementia and Its Major Subtypes.

: Type 2 diabetes mellitus (T2DM) is a major contributor to cognitive decline and dementia in older adults; however, the role of the age of onset of T2DM in younger patients remains uncertain. We explored the association between the risk of dementia and its subtypes in relation to the age at T2DM diagnosis. This population cohort study included a total of 612,201 newly diagnosed T2DM patients. The controls were randomly selected from the general population and matched at a 1:2 ratio based on the propensity score. The outcomes of interest were all-cause dementia, Alzheimer's disease (AD), and vascular dementia (VD). The association of T2DM with dementia was stratified by the age at diagnosis of T2DM. : The mean ages of the subjects in the T2DM and control groups were 55.7 ± 13.0 and 55.7 ± 13.0. The patients with T2DM diagnosed at <50 years had the highest excess risk for most outcomes relative to the controls, with a hazard ratio (HR) (95% CI) of 3.29 (3.11-3.49) for all-cause dementia, 4.08 (3.18-5.24) for AD, and 5.82 (3.84-8.81) for VD. All risks were attenuated progressively with each increasing decade at the diagnostic age, but remained significant; for T2DM diagnosed at ≥80 years, the HR (95% CI) was 1.38 (1.34-1.41) for all-cause dementia, 1.35 (1.31-1.40) for AD, and 1.98 (1.70-2.30) for VD. : We need to stratify T2DM management according to the age of diagnosis. Physicians should closely monitor cognitive function in patients with T2DM, especially in younger individuals.