Long-term Glycemic Control and Dementia Risk in Type 1 Diabetes

OBJECTIVE Individuals with type 1 diabetes have experienced an increase in life expectancy; yet, it is unknown what level of glycemic control is ideal for maintaining late-life brain health. We investigated the association of long-term glycemic control with dementia in older individuals with type 1 diabetes. RESEARCH DESIGN AND METHODS We followed 3,433 members of a health care system with type 1 diabetes, ages ≥50 years, from 1996 to 2015. Repeated measurements of hemoglobin A 1c (HbA 1c ), dementia diagnoses, and comorbidities were ascertained from health records. Cox proportional hazards models were fit to evaluate the association of time-varying glycemic exposure with dementia, with adjustment for age, sex, race/ethnicity, baseline health conditions, and frequency of HbA 1c measurement. RESULTS Over a mean follow-up of 6.3 years, 155 individuals (4.5%) were diagnosed with dementia. Patients with ≥50% of HbA 1c measurements at 8–8.9% (64–74 mmol/mol) and ≥9% (≥75 mmol/mol) had 65% and 79% higher risk of dementia, respectively, compared with those with 1c 8–8.9% adjusted hazard ratio [aHR] 1.65 [95% CI 1.06, 2.57] and HbA 1c ≥9% aHR 1.79 [95% CI 1.11, 2.90]). By contrast, patients with ≥50% of HbA 1c measurements at 6–6.9% (42–52 mmol/mol) and 7–7.9% (53–63 mmol/mol) had a 45% lower risk of dementia (HbA 1c 6–6.9% aHR 0.55 [95% CI 0.34, 0.88] and HbA 1c 7–7.9% aHR 0.55 [95% CI 0.37, 0.82]). CONCLUSIONS Among older patients with type 1 diabetes, those with majority exposure to HbA 1c 8–8.9% and ≥9% had increased dementia risk, while those with majority exposure to HbA 1c 6–6.9% and 7–7.9% had reduced risk. Currently recommended glycemic targets for older patients with type 1 diabetes are consistent with healthy brain aging.