Age of Type 1 Diabetes Onset and Dementia Risk: A Swedish Nationwide, Register‐Based Cohort Study

ABSTRACT Aims Individuals with Type 1 diabetes are at a higher risk of dementia compared to individuals without diabetes. Younger age at Type 1 diabetes onset has been linked to an increased risk of cardiovascular disease and higher mortality. This study aimed to determine whether younger age at Type 1 diabetes onset was also associated with all‐cause dementia. Materials and Methods This nationwide prospective cohort study used data from individuals with Type 1 diabetes from the Swedish National Diabetes Register. All‐cause dementia, including Alzheimer's disease, vascular dementia and non‐Alzheimer's‐non‐vascular dementia, was prospectively ascertained as ICD‐10 codes. Age at onset was stratified into < 10 years, 10–17 years and 18–30 years. The 18–30 years group was used as the reference group for all analyses. Cox regression modelling with age as the time‐axis, from age at diabetes onset, was deployed to investigate dementia risk. Results Of 43 440 included individuals (mean age 33.0 (SD 14.0) years; 44% female), Type 1 diabetes developed before age 10 in 11 776 individuals (27%), between age 10 and 17 in 15 846 (36%) and between 18 and 30 (reference group) in 15 818 (36%). During a median 29.3 17.6–43.7 years follow‐up, 530 (1.2%) developed all‐cause dementia. Compared to the reference group, all‐cause dementia risk was increased in individuals aged < 10 years at onset (HR 1.37 95% CI 1.08–1.73), but not in individuals aged 10–17 years at onset (HR 1.04 95% CI 0.85–1.26) (fully adjusted model). Conclusions Type 1 diabetes onset before age 10 is associated with an increased risk of all‐cause dementia compared to onset between ages 18 and 30.