Impact of type 2 diabetes and glycated hemoglobin levels within the recommended target range on mortality in older adults with cognitive impairment receiving care at a memory clinic: NCGG-STORIES

Objective: To determine the impact of type 2 diabetes and glycated hemoglobin (HbA1c) levels within the recommended target range according to the Japan Diabetes Society/Japan Geriatrics Society Joint Committee on mortality in older adults with cognitive impairment.

Research Design and Methods: This retrospective cohort study included 1,528 and 468 patients aged ≥65 years without and with type 2 diabetes, respectively, who were visiting a memory clinic. The 468 patients with type 2 diabetes were divided into three groups (within/above/below the target range) based on their HbA1c levels, cognitive function, ability to perform activities of daily living, and medications associated with a high risk of hypoglycemia. The impact of diabetes and HbA1c levels on mortality was evaluated using Cox proportional hazard models.

Results: Over a median follow-up period of 3.8 years, 353 patients (17.7%) died. Compared with individuals without type 2 diabetes, HbA1c levels above (hazard ratio [HR] = 1.70, 95% confidence interval [CI] = 1.08–2.69) and below (HR = 2.15, 95% CI = 1.33–3.48) the target range were associated with a higher risk of death; however, HbA1c levels within the target range were not (HR = 1.02, 95% CI = 0.77–1.36).

Conclusions: HbA1c levels above and below the target range were associated with a higher risk of mortality, whereas patients with HbA1c levels within the target range did not exhibit a higher risk of mortality than individuals without type 2 diabetes. These results provide empirical support for the current target ranges among older adults with cognitive impairment.