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.