Insulin resistance and cognitive performance in type 2 diabetes : The Maastricht study

AIMS: Type 2 diabetes, hyperinsulinemia, and insulin resistance are associated with cognitive impairment. Experimental studies indicate that insulin signaling in the brain is related to cognitive performance. Here we evaluated whether insulin-related variables contribute to the variance in cognitive performance among individuals with type 2 diabetes. METHODS: A total of 806 individuals with type 2 diabetes (mean age 62±8years, HbA1c 6.9±1.1%) completed a neuropsychological test battery. Insulin-related variables evaluated were: fasting plasma insulin, C-peptide, and the Homeostasis Model Assessment (HOMA2-IR; in individuals without insulin treatment; n=641). The unadjusted coefficient of determination (R(2)), obtained from multiple linear regression analyses, was used to estimate the proportion of variance in cognition explained by insulin-related variables. RESULTS: Sex, age, and educational level together explained 18.0% (R(2)) of the variance in memory function, 26.5% in information processing speed, and 22.8% in executive function and attention. Fasting insulin, C-peptide, or HOMA2-IR did not increase the explained variance (maximum ΔR(2) 0.3%, P≥0.14). Similar results were obtained when insulin-related variables were added to models that additionally included glycemic control, cardiovascular risk factors, and depression. CONCLUSIONS: Our results show that measures of peripheral insulin resistance are unrelated to cognitive performance among individuals with adequately controlled type 2 diabetes