Analysis of factors influencing pancreatic beta-cell function in Japanese patients with type 2 diabetes: association with body mass index and duration of diabetic exposure.

AIMS: To elucidate the clinical factors affecting beta-cell function, serum C-peptide immunoreactivity (CPR) levels of patients with type 2 diabetes were analyzed. METHODS: Seven hundred Japanese patients with type 2 diabetes were enrolled. beta-Cell function was evaluated by fasting CPR (FCPR), 6 min after intravenous injection of 1mg glucagon (CPR-6 min), and the increment of CPR (DeltaCPR). Simple regression analysis between FCPR, CPR-6 min, and DeltaCPR and measures of variables and stepwise multiple regression analysis were carried out. RESULTS: Years from diagnosis and BMI were the major independent variables predicting beta-cell function. Years from diagnosis was negatively correlated with CPR-6 min (P<0.0001, r=-0.271), and decrease in CPR-6 min was 0.050 ng/(ml year). BMI was positively correlated with CPR-6 min (P<0.0001, r=0.369). When subjects were divided according to BMI, the decrease in CPR-6 min per year in the high-BMI group (0.068 ng/(ml year)) was greater than that in the low-BMI group (0.035 ng/(ml year)). CONCLUSION: A linear decline in endogenous insulin secretion over more than several decades of diabetes was confirmed by this cross-sectional study. The duration of diabetes exposure and BMI are thus major factors in beta-cell function in Japanese patients with type 2 diabetes.