2.2 Clinical and biochemical measurements
We used a questionnaire administered by an interviewer to obtain information. The questionnaire primarily included demographic factors, lifestyle factors, medical history and family history. The Mandarin Chinese language was used to design the questionnaire, and the questionnaire was administered in Chinese by investigators who could speak Mandarin Chinese as well as Cantonese, and they have received uniform training on the administration of the questionnaire. Education was divided into three levels: low (primary school and illiteracy), median (middle and high school) and high (university and above). Total yearly income for family was classified into three groups: ≤10,000 yuan/year, 10,000-50,000 yuan/year and ≥50,000 yuan/year. Smoking habits were classified as ”never”, ”occasionally” (<1 time/day currently or in the past 6 months), and ”frequently” (≥1 times/day currently or in the past 6 months). Alcohol consumption habits were classified as ”never”, ”occasionally” (alcohol consumption for socializing currently or in the past 6 months), and ”frequently” (≥3 times/week or alcohol consumption everyday currently or in the past 6 months).
All participants completed the anthropometrical measurements with the assistance of trained staff using standard protocols. Height and weight were measured using standard protocols, without shoes or outerwear. Body weight and height were measured twice during the examination and recorded to the nearest 0.1 kg and 0.1 cm and the average of two weight and height measurements were used for analysis. Body mass index (BMI) was calculated as weight (kg) divided by height squared (m2). BMI was used to describe general obesity, subjects were categorized as underweight (<18.5 kg/m2), normal weight (18.5 to 23.9 kg/m2), overweight (24.0 to 27.9 kg/m2), or obese (≥28.0 kg/m2). Waist circumference (WC) was measured to the nearest 0.1 cm at the umbilicus. WC ≥ 80.0 cm in females and ≥ 85.0 cm in males were defined as central obesity. In addition, repeated blood pressure measurements were performed by the same observer three times with a 5 min interval between readings using an automated electronic device (OMRON, Omron Company, Dalian, China). The average of three blood pressure measurements were collected and used for analysis. Hypertension was diagnosed by systolic blood pressure (SBP) greater than or equal to 140 mmHg and/ or diastolic blood pressure (DBP) greater than or equal to 90 mmHg, or diagnosed by a doctor as hypertension. Participants were examined in the supine position with the neck hyperextended. Thyroid ultrasonography of all participants was performed by the same certified sonographer using 7.5 MHz ultrasound probes (Logiq 500 Pro, GE Medical Systems, WI, and USA). Thyroid nodules were defined as discrete lesion(s) within the thyroid gland that is palpable and/or ultrasonographically distinct from the surrounding thyroid parenchyma[18].
Venous blood samples were collected and stored at -80℃ for laboratory tests after an overnight fasting of at least 10 hours. Measurements of fasting plasma glucose (FPG), oral glucose tolerance test (OTGG), triglycerides (TG), total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), alanine aminotransferase (ALT) and creatinine (Cr) were performed using an autoanalyser (Beckman CX-7 Biochemical Autoanalyser, Brea, CA, USA). HemoglobinA1c (HbA1c) was assessed by high-performance liquid chromatography (Bio-Rad, Hercules, CA). Diabetes was diagnosed according to the 1999 WHO diagnostic criteria, fasting blood glucose (FBG) ≥7.0 mmol/L and/ or oral glucose tolerance test (OGTT) ≥11.1 mmol/L, or diagnosed by a doctor as diabetes.