Diabetes, glucose control, and 9-year cognitive decline among older adults without dementia.

OBJECTIVES To determine if prevalent and incident diabetes mellitus (DM) increase risk of cognitive decline and if, among elderly adults with DM, poor glucose control is related to worse cognitive performance. DESIGN Prospective cohort study. SETTING Health, Aging, and Body Composition Study at 2 community clinics. PARTICIPANTS A total of 3069 elderly adults (mean age, 74.2 years; 42% black; 52% female). MAIN OUTCOME MEASURES Participants completed the Modified Mini-Mental State Examination (3MS) and Digit Symbol Substitution Test (DSST) at baseline and selected intervals over 10 years. Diabetes mellitus status was determined at baseline and during follow-up visits. Glycosylated hemoglobin A1c level was measured at years 1 (baseline), 4, 6, and 10 from fasting whole blood. RESULTS At baseline, 717 participants (23.4%) had prevalent DM and 2352 (76.6%) were without DM, 159 of whom developed incident DM during follow-up. Participants with prevalent DM had lower baseline test scores than participants without DM (3MS: 88.8 vs 90.9; DSST: 32.5 vs 36.3, respectively; t = 6.09; P = .001 for both tests). Results from mixed-effects models showed a similar pattern for 9-year decline (3MS: -6.0- vs -4.5-point decline; t = 2.66; P = .008; DSST: -7.9- vs -5.7-point decline; t = 3.69; P = .001, respectively). Participants with incident DM tended to have baseline and 9-year decline scores between the other 2 groups but were not statistically different from the group without DM. Multivariate adjustment for demographics and medical comorbidities produced similar results. Among participants with prevalent DM, glycosylated hemoglobin A1c level was associated with lower average mean cognitive scores (3MS: F = 8.2; P for overall = .003; DSST: F = 3.4; P for overall = .04), even after multivariate adjustment. CONCLUSION Among well-functioning older adults, DM and poor glucose control among those with DM are associated with worse cognitive function and greater decline. This suggests that severity of DM may contribute to accelerated cognitive aging.