Risk of Ischemic and Hemorrhagic Stroke in Individuals With Type 1 and Type 2 Diabetes: A Nationwide Cohort Study in Sweden

Background and Objectives Diabetes significantly increases the risk of cardiovascular events, including stroke. Although the association with ischemic stroke is well established, the relationship with hemorrhagic stroke remains unclear. This study aimed to evaluate the risk of ischemic and hemorrhagic stroke in individuals with type 1 and type 2 diabetes compared with diabetes-free controls from the general population. Methods This cohort study included individuals with type 1 or type 2 diabetes from the Swedish National Diabetes Register between 2005 and 2019, matched to diabetes-free controls by age and sex. Data on baseline characteristics, comorbidities, medications, and outcomes were collected from multiple national registers. Stroke incidence rates and adjusted hazard ratios were estimated using Cox proportional hazard models, stratified by diabetes type, for ischemic and hemorrhagic stroke. Results The study included 47,720 individuals with type 1 diabetes (mean age 34.4, 44.8% female) and 686,158 with type 2 diabetes (mean age 65.3, 43.3% female), matched to 143,160 and 2,058,474 controls, respectively. In individuals with type 1 diabetes, the ischemic stroke risk was 2.54 times higher (95% CI 2.36-2.73) and the hemorrhagic stroke risk was 1.88 times higher (95% CI 1.57-2.26) compared with controls. In individuals with type 2 diabetes, the ischemic stroke risk was 1.37 times higher (95% CI 1.35-1.38) while the hemorrhagic stroke risk was not significantly increased (HR: 0.99, 95% CI 0.96-1.02). Higher HbA1c levels were associated with increased ischemic stroke risk for both diabetes types. For hemorrhagic stroke, individuals with type 1 diabetes had significantly higher risk starting at HbA1c > 52 mmol/mol while in those with type 2 diabetes, a modest risk increase was observed only at HbA1c > 72 mmol/mol. Discussion The risk of ischemic stroke was higher for both diabetes types. Individuals with type 1 diabetes also exhibited a higher risk of hemorrhagic stroke compared with diabetes-free controls while type 2 diabetes was significantly associated with risk of hemorrhagic stroke only when HbA1c was higher than 72 mmol/mol. These findings highlight the increased stroke risk in diabetes, with distinct patterns by stroke subtype and diabetes type. Tailored prevention strategies are essential to address these differences.