Age at T1D Onset and Dementia Risk
Milena Jancev, Björn Eliasson, Geert Jan Biessels, J. Hans DeVries, Erik H. Serné, Frank L. J. Visseren, Araz Rawshani, Aidin Rawshani, Tali Cukierman-Yaffe, Naveed Sattar, Hertzel C. Gerstein, Thomas T. van Sloten.
Age of Type 1 Diabetes Onset and Dementia Risk: A Swedish Nationwide, Register-Based Cohort Study. Diabetes Obes Metab. 2026 Jul 19. Online ahead of print.
People with type 1 diabetes (T1D) already carry a higher risk of dementia than those without diabetes. A younger age at T1D onset has separately been linked to a higher lifetime risk of cardiovascular disease and mortality — but whether onset age also shapes dementia risk was unknown. This study, conducted by researchers from University Medical Center Utrecht and Sahlgrenska University Hospital Gothenburg, used the Swedish National Diabetes Register to test whether developing T1D earlier in life is associated with a higher risk of all-cause dementia decades later.
The researchers followed 43,440 individuals with T1D, grouped by age at onset (<10 years, 10–17 years, and 18–30 years, the latter used as the reference group), over a median of 29.3 years, using age itself as the time axis in Cox regression models adjusted for sex, region of birth, education and marital status.
Key findings:
- Onset before age 10 carries a higher dementia risk: Compared with onset between 18–30 years, individuals diagnosed before age 10 had a 37% higher risk of all-cause dementia (HR 1.37, 95% CI 1.08–1.73), even though their crude incidence rate was lower — because dementia occurred at a younger age in this group.
- No increased risk for onset between 10–17 years: This intermediate group did not differ significantly from the reference group (HR 1.04, 95% CI 0.85–1.26).
- A consistent gradient in cumulative incidence: By age 75, cumulative dementia incidence ranged from 4.85% (onset 18–30 years) to 6.75% (onset before age 10), with dementia diagnosed at a notably younger median age (66.3 vs. 72.8 years) in the earliest-onset group.
- Vascular dementia drives the subtype signal: Among dementia subtypes, only vascular dementia was significantly elevated in the youngest-onset group (HR 1.65, 95% CI 1.10–2.47); Alzheimer's disease and other dementia showed no significant differences.
- The association strengthened after adjusting for diabetes duration: far from explaining away the effect, accounting for diabetes duration increased the hazard ratios (HR 2.14 for <10 years; HR 1.33 for 10–17 years), suggesting duration alone doesn't account for the excess risk.
- Robust across sensitivity analyses: results held using a broader T1D definition, when starting follow-up at cohort entry rather than diagnosis, and after additional adjustment for cardiovascular history, ketoacidosis and calendar year.
The authors propose that early-onset T1D reflects a more aggressive disease phenotype — rapid beta-cell loss, higher glycaemia, heightened systemic inflammation — striking a still-developing brain that may be particularly vulnerable to these insults, on top of decades of longer cumulative exposure to hyperglycaemia and vascular damage..
Concluding, the authors state
"A younger age at Type 1 diabetes onset (<10 years) was associated with a higher risk of all-cause dementia compared with later onset (18–30 years)"
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