Introduction: The impact of prediabetes and diabetes on stroke and the development of dementia after a stroke remain unclear.

Methods: A total of 2655 dementia-free participants (including a stroke-free cohort and a prevalent stroke cohort) were followed-up for 12 years. Dementia and post-stroke dementia were determined by clinical examinations and national registry data. Diabetes was ascertained via medical examination, medication use, medical records, or glycated hemoglobin (HbA1c) >= 6.5%. Prediabetes was defined as H bA1c >= 5.7% in diabetes-free participants.

Results: In the stroke-free cohort, 236 participants developed ischemic stroke, and 47 developed post-stroke dementia. Diabetes was associated with ischemic stroke (hazard ratio [HR] 1.76, 95% confidence interval [CI] 1.16 to 2.67) and post-stroke dementia (HR 2.56, 95% CI 1.04 to 6.25). In the prevalent stroke cohort, diabetes was also related to dementia risk. Prediabetes was not significantly related to stroke or post-stroke dementia.

Discussion: Diabetes, but not prediabetes, is associated with an increased risk of ischemic stroke and post-stroke dementia.