Plasma interleukin-6 levels are increased in subjects with impaired glucose tolerance but not in those with impaired fasting glucose in a cohort of Italian Caucasians

Background: While the relationship between impaired glucose tolerance (IGT) and circulating interleukin-6 (IL-6) is well established, there is no information whether IL-6 levels are elevated in impaired fasting glucose (IFG).

Methods: To this end, we examined the relationship between plasma IL-6 concentration and different degrees of glucose homeostasis in a cohort of 470 Italian Caucasian subjects comprising 236 normal glucose tolerant (NGT), 49 IFG, 51 IGT, and 134 type 2 diabetic subjects.

Results: We observed that IL-6, CRP and fibrinogen levels were higher in subjects with IGT or type 2 diabetes as compared with NGT and IFG subjects. Univariate correlations between IL-6 concentrations and metabolic variables in the whole cohort showed that IL-6 levels were positively correlated with age, BMI, waist, systolic and diastolic blood pressure, fasting plasma glucose, triglycerides, CRP, fibrinogen, and negatively correlated with insulin sensitivity, IGF-I and HDL. In a subgroup analysis including NGT, IFG and IGT (n = 336), IL-6 levels were positively correlated with age, BMI, waist, systolic and diastolic blood pressure, triglycerides, CRP, fibrinogen, fasting insulin, 2 h post-load glucose, and negatively correlated with insulin sensitivity, IGF-I and HDL. Stepwise linear regression analysis in a model including gender, age, BMI, waist, glucose tolerance status, fasting plasma glucose, 2 h post-load glucose, triglycerides, HDL, fasting insulin, and insulin sensitivity revealed that waist was the only independent variable associated with IL-6 levels accounting for 21.0% of its variation (P < 0.0001).

Conclusions: These data show that IGT and type 2 diabetes, but not IFG, are associated with elevated plasma IL-6 levels.