2.2 Clinical and biochemical measurement
A standardized questionnaire was used to collect baseline data, and was administered by trained interviewers during a face-to-face interview. Information collected included lifestyle factors, socio-demographic characteristics, and family history. Current smoking and drinking status were divided into 3 groups: never, ever (the cessation of smoking and drinking for more than half a year), and current (smoking or drinking regularly in the recent half year). The frequency and duration of physical activity were obtained using the International Physical Activity Questionnaire (IRAQ), and the level of physical activity was evaluated by calculating the metabolic equivalent hours per week (MET-h/week).
Anthropometrical examinations were conducted by trained staff using standard protocols. Body weight and height were measured with subjects wearing light indoor clothing without shoes, and recorded to the nearest 1.0 kg and 0.1 cm, respectively. Body mass index (BMI) was calculated as weight in kilograms divided by height in meters squared (kg/m2), and BMI was used to define obesity. Obesity was defined as a BMI ≥ 28.0 kg/m2, and overweight when 24.0 kg/m2 ≤ BMI < 28.0 kg/m2. Waist circumference (WC) was measured at the umbilical level to the nearest 0.1 cm with subjects in the standing position using a non-elastic measuring tape. Central obesity was defined as a WC ≥ 90 cm in men and ≥ 80 cm in women. Blood pressure was obtained with the subject seated 3 consecutive times at 5 minutes intervals using an automated electronic device (OMRON, Omron Company, Dalian, China). The average of the 3 measurement was used in the analysis. Hypertension was defined as a systolic blood pressure (SBP) ≥ 140 mmHg or a diastolic blood pressure (DBP) ≥ 90 mmHg or the subject reporting that they were receiving regular anti-hypertensive treatment
After an overnight fast of at least 10 hours, venous blood samples were collected and stored at 80 ºC until testing. All patients also received a 2h OGTT. Measurements of FPG, 2h OGTT, fasting serum insulin, total cholesterol (TC), triglycerides (TG), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), aspartate aminotransferase (AST), alanine aminotransferase (ALT), and γ-glutamyltransferse (γ-GGT) was done using an automated electronic device (Beckman CX-7 Biochemical Autoanalyzer, Brea, California, USA). HbA1c was measured by high-performance liquid chromatography (BioRad, Hercules, CA).  HOMA-β was calculated using the formula: HOMA-β = 20 × (fasting plasma insulin, μU/mL) / (FPG, mmol/L) – 3.5. HOMA-IR was calculated using the formula: HOMA-IR = (FPG, mmol/L) × (fasting plasma insulin, μU/ml) / 22.518. The abbreviated Modification of Diet in Renal Disease (MDRD) formula recalibrated for the Chinese population was used to calculate the estimated glomerular filtration rate (eGFR) expressed as mL/min per 1.73 m2. The formular is: eGFR = 175 × (serum creatinine × 0.011)-1.234 × (age)-0.179 × (0.79 if female), with serum creatinine was expressed as μmol/L. Diabetes was diagnosed according to the 1999 WHO diagnostic criteria, the level of FPG ≥ 7.0 mmol/L or the level of 2h OGTT ≥ 11.1 mmol/L19.