Association of duration and severity of diabetes mellitus with mild cognitive impairment

Background: It remains unknown whether diabetes mellitus (DM) is a risk factor for mild cognitive impairment (MCI). Objective: To investigate the association of DM with MCI using a population-based case-control design. Design: Population-based case-control study. Setting: Academic research. Participants: Our study was conducted, among subjects aged 70 to 89 years on October 1, 2004, who were randomly selected from the Olmsted County (Minnesota) population. Main Outcome Measure: We administered to all participants a neurologic examination, the Clinical Dementia Rating Scale, and a neuropsychological evaluation (including 9 tests in 4 cognitive domains) to diagnose normal cognition, MCI, or dementia. We assessed history of DM, DM treatment, and DM complications by interview, and we measured fasting blood glucose levels. History of DM was also confirmed using a medical records linkage system. Results: We compared 329 subjects having MCI with 1640 subjects free of MCI and dementia. The frequency of DM was similar in subjects with MCI (20.1%) and in subjects without MCI (17.7%) (odds ratio [OR], 1.16; 95% confidence interval [CI], 0.85-1.57). However, MCI was associated with onset of DM before age 65 years (OR, 2.20; 95% CI, 1.29-3.73), DM duration of 10 years or longer (OR, 1.76; 95% CI, 1.16-2.68), treatment with insulin (OR, 2.01; 95% CI, 1.22-3.31), and the presence of DM complications (OR, 1.80; 95% CI, 1.13-2.89) after adjustment for age, sex, and education. Analyses using alternative definitions of DM yielded consistent findings. Conclusion: These findings suggest an association of MCI with earlier onset, longer duration, and greater severity of DM.