Predictors of insulin sensitivity in Type 2 diabetes mellitus

Aims To identify the independent predictors of insulin sensitivity in Type 2 diabetes, and to establish whether isolated Type 2 diabetes (i.e. diabetes without overweight, dyslipidaemia and hypertension) is a condition of insulin resistance. Methods We examined 45 patients with non-insulin-treated Type 2 diabetes undergoing a 4-h euglycaemic hyperinsulinaemic clamp (20 mU/m(2) per min) combined with H-3-3-D-glucose and C-14-U-glucose infusions and indirect calorimetry. We also examined 1366 patients with non-insulin-treated Type 2 diabetes randomly selected among those attending the Diabetes Clinic and in whom insulin resistance was estimated by Homeostasis Model Assessment (HOMA-IR). Results In the 45 patients undergoing glucose clamp studies, insulin-mediated total glucose disposal (TGD) was independently and negatively associated with systolic blood pressure (standardized beta coefficient = -0.407, F = 0.003), plasma triglycerides (beta = -0.355, P = 0.007), and HbA(1c) (P = -0.350, P = 0.008). The overall variability of TGD explained by these variables was 53%. Overweight diabetic subjects with central fat distribution, hypertension, hypertriglyceridaemia and poor glycometabolic control had insulin-mediated TGD values markedly lower than their lean counterparts without hypertension, with normal triglycerides, and with good glycometabolic control (16 +/- 5 vs. 31 +/- 10 mumol/min per kg lean body mass, P < 0.01). Nevertheless, the latter still were markedly insulin-resistant when compared with sex- and age-matched non-diabetic control subjects (31 +/- 10 vs. 54 +/- 13 mu mol/min per kg lean body mass, P < 0.01). In the 1366 Type 2 diabetic patients of the epidemiological study, HOMA-IR value was independently associated with HbA(1c) (beta = 0.283, P < 0.0001), plasma triglycerides (beta = 0.246, P < 0.0001), body mass index (beta = 0.139, P < 0.001), waist girth (beta=0.124, P<0.001) and hypertension (beta=0.066, P = 0.006). Conclusion Overweight, central fat distribution, dyslipidaemia, hypertension and poor glycometabolic control are strong independent predictors of insulin resistance in Type 2 diabetes. However, reduced insulin sensitivity can be found even when Type 2 diabetes is isolated and well controlled.