Background: The long-term effect of type 2 diabetes on cognitive function is uncertain.
Objective: To determine whether older women with diabetes have an increased risk of cognitive impairment and cognitive decline.
Design: Prospective cohort study.
Setting: Four research centers in the United States (Baltimore, Md; Portland, Ore; Minneapolis, Minn; and the Monongahela Valley, Pennsylvania).
Participants: Community-dwelling white women 65 years and older (n = 9679).
Measurements: Physician-diagnosed diabetes and other aspects of health history were assessed by interview. Three tests of cognitive function, the Digit Symbol test, the Trails B test, and a modified version of the Mini-Mental State Examination (m-MMSE), were administered at baseline and 3 to 6 years later. Change in cognitive function was defined by the change in the score for each test. Major cognitive decline was defined as the worst 10th percentile change in the score for each test.
Results: Women with diabetes (n = 682 [7.0%]) had lower baseline scores than those without diabetes on all 3 tests of cognitive function (Digit Symbol and Trials B tests, P<.01; m-MMSE, P = .03) and experienced an accelerated cognitive decline as measured by the Digit Symbol test (P<.01) and m-MMSE (P = .03). Diabetes was also associated with increased odds of major cognitive decline as determined by scores on the Digit Symbol (odds ratio = 1.63; 95% confidence interval, 1.20-2.23) and Trails B (odds ratio, 1.74; 95% confidence interval, 1.27-2.39) tests when controlled for age, education, depression, stroke, visual impairment, heart disease, hypertension, physical activity, estrogen use, and smoking. Women who had diabetes for more than 15 years had a 57% to 114% greater risk of major cognitive decline than women without diabetes.
Conclusion: Diabetes is associated with lower levels of cognitive function and greater cognitive decline among older women.