Diverse effect of inflammatory markers on insulin resistance and insulin-resistance syndrome in the elderly

OBJECTIVES: To evaluate the potential association between different inflammatory markers and insulin resistance (IR), as well as insulin-resistance syndrome (IRS) in a large, population-based study of older, nondiabetic persons. DESIGN: Cross-sectional study. SETTING: Outpatient clinic in Greve in Chianti and Bagno a Ripoli (Italy). PARTICIPANTS: One thousand one hundred forty-six nondiabetic subjects ranging in age from 22 to 104. MEASUREMENTS: Anthropometric measurements; plasma fasting levels of glucose, insulin, and cholesterol (total, high-density lipoprotein, low-density lipoprotein); homeostasis model assessment to estimate degree of insulin resistance; tumor necrosis factor alpha (TNF-alpha), interleukin 6 (IL-6), soluble IL-6 receptor (sIL-6R), interleukin receptor antagonist (IL-1ra), and C-reactive protein (CRP) plasma concentrations; diastolic, systolic, and mean arterial blood pressure; and echo-color-Doppler duplex scanning examination of carotid arteries. RESULTS: Insulin resistance correlated with age (r=0.102; P<.001) and plasma levels of TNF-alpha (r=0.082; P=.007), IL-1ra (r=0.147; P<.001), IL-6 (r=0.133; P<.001), sIL-6R (r=-0.156; P<.001), and CRP (r=0.83; P<.001). Subjects in the upper tertile of IR degree were older and had higher serum levels of TNF-alpha, IL-1ra, and IL-6 and lower levels of sIL-6R than subjects in the lowest tertile. Independent of age, sex, body mass index, waist-to-hip ratio, triglycerides, drug intake, diastolic blood pressure, smoking habit, and carotid atherosclerotic plaques, higher IL-6 (t=2.987; P=.003) serum concentrations were associated with higher IR, whereas sIL-6R levels (t=-5.651; P<.001) were associated with lower IR. Furthermore, IL-1ra concentrations (t=2.448; P=.015) were associated with IRS, and higher sIL-6R plasma levels continued to correlate negatively with IRS. CONCLUSION: Different inflammatory markers are associated with a diverse effect on IR and IRS in elderly nondiabetic subjects.