Insulin Resistance and Executive Dysfunction in Older Persons

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Abstract
Objectives: To evaluate the association between insulin resistance (IR) and executive dysfunction in a large, population‐based study of older persons without diabetes mellitus (DM) or dementia. Design: Cross‐sectional study. Setting: Outpatient clinic in Greve in Chianti and Bagno a Ripoli, Italy. Participants: A total of 597 subjects aged 65 to 93 without DM or dementia. Measurements: Anthropometric measurements; plasma fasting levels of glucose, insulin, cholesterol (total cholesterol, high‐density lipoprotein cholesterol (HDL‐C), low‐density lipoprotein cholesterol), and insulin‐like growth factor‐1 (IGF‐1); homeostasis model assessment (HOMA) to estimate degree of IR; Trail Making Test (TMT) A; TMT‐B; TMT‐B minus TMT‐A (DIFF B–A); and Mini‐Mental State Examination (MMSE). Results: IR (HOMA) was associated with longer TMT‐B (correlation coefficient (r)=0.11; P=.006) and DIFF B–A times (r=0.10; P=.022). Subjects in the upper tertile of IR were older and had longer TMT‐B and DIFF B–A than participants in the lowest tertile. After adjusting for age, sex, and years of formal education, IR was significantly correlated with TMT‐A, TMT‐B, and DIFF B–A. After adjusting for age, sex, education, body mass index, waist:hip girth ratio, HDL‐C, triglycerides, IGF‐1, hypertension, drug intake, and physical activity, the results did not significantly change. After introducing MMSE score into the model, IR continued to be an independent determinant of TMT‐A (β=11.005; P=.021), TMT‐B (β=28.379; P<.001), and DIFF B–A (β=17.374; P=.011). Conclusion: IR is independently associated with frontal cortex function evidenced by poor TMT times in older persons without DM or dementia.