Blood sampling and biochemical measurement
After an overnight fasting, venous blood samples were collected into tubes containing EDTA and sodium fluoride. Plasma specimens were separated. Samples were kept refrigerated or frozen depending on the time of analysis. Moreover, a portion of the whole blood sample was stored for A1c measurement. Biochemical analyses were performed with the Cobas C311 autoanalyzer using commercial kits from Roche Company (Roche Diagnostics, Mannheim, Germany). Two levels of quality control sera were analyzed in each run. The calculated inter-assay precisions (coefficient of variation%) were less than 1.1%, 3%, 3.2%, 1.8%, and 1.7% for glucose, HbA1c, high-density lipoprotein (HDL) cholesterol, triglyceride, and total cholesterol, respectively. In addition, non-HDL cholesterol was calculated by subtracting HDL cholesterol from total cholesterol.