Objective: In this study, we examined the association of non-insulin-dependent diabetes mellitus (NIDDM) and impaired glucose tolerance (IGT) with cognitive function in a population-based sample of older individuals.
Research design and methods: Subjects were 1509 healthy, community-dwelling men and women aged 55 years and older who were participants in the Rancho Bernardo Study and attended clinic visits in 1984-87 and in 1988-91. An oral glucose tolerance test was administered during the 1984-87 visits. Based on World Health Organization criteria, participants were classified into those with NIDDM, IGT, or normal glucose tolerance. During the 1988-91 clinic visits, 12 tests of cognitive function were administered.
Results: Of the participants, 14.3% of the men and 9.9% of the women had NIDDM, and 21.0% of the men and 28.0% of the women had IGT. Multiple regression analysis was used to compare the cognitive function of individuals with NIDDM and IGT with individuals with normal glucose tolerance after adjustment for age, education, obesity, depression, blood pressure, and current estrogen use. In men, there were no statistically significant differences in any of the 12 cognitive function tests by glucose tolerance category. Compared with those with normal glucose tolerance, women with IGT had lower scores on almost every cognitive function test, whereas women with NIDDM had higher scores, but none of these differences were statistically significant after adjustment for multiple comparisons. Furthermore, observed differences by NIDDM or IGT status were small and accounted for < or = 0.6% of the explained variance in cognitive function.
Conclusions: This study shows no strong or consistent association between IGT or mild diabetes with cognitive function in community-dwelling older adults.