Abstract

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, and 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 hazards 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% 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.