The Asymptomatic Polyvascular Abnormalities Community (APAC) study is a community-based observational prospective, long-term follow-up study to investigate the epidemiology of asymptomatic polyvascular abnormalities in Chinese adults [14]. The study cohort was a subgroup of a previously described population of the Kailuan study [15]. Data about patient demographics , clinical characteristics (physical examination, laboratory tests, carotid duplex ultrasound and transcranial Doppler examinations), and also finished structured interviews with a standardized questionnaire performed by trained investigators. Anthropometric indices included height and weight. Body mass index (BMI) was calculated as body weight (kg) divided by the square of body height (m²). Blood pressure was measured twice with an appropriate cuff size in relation to arm size, in the participants with the supine position after 10 min resting. The average of the two readings was used. However, if the difference between the two measurements exceeded 5 mmHg, a third reading would be conducted, and the average of three readings was recorded and analyzed. Smoking was defined as at least one cigarette per day for more than a year. Alcohol abuse was defined as alcohol intake of at least 90 and 45 g of liquor a day for men and women, respectively, for more than 1 year. Smoking or drinking cessation was considered only if it lasted for at least 1 year. Details of the APAC study design and the information on baseline characteristics have been published previously. The community is part of a large coal mining industry in Tangshan, Hebei Province [15, 16], China. The study protocol was approved by the Ethics Committees of the Kailuan General Hospital and the Beijing Tiantan Hospital, and informed consent was obtained from all participants.

MetS was defined using previously published criteria from the International Diabetes Federation [11]. The definition included the presence of central obesity (waist circumference >90 cm for Chinese men and >80 cm for Chinese women), plus any two of the following factors: triglycerides >150 mg/dl (1.7 mmol/L) or obtaining therapy for increased triglyceride (TG) concentrations; high-density lipoprotein cholesterol (HDL-C), 40 mg/dl (1.03 mmol/L) in men and 50 mg/dl (1.29 mmol/L) in women, or obtaining therapy for low HDL-C level; systolic blood pressure (BP) >130 mmHg or diastolic BP >85 mmHg, or treatment of previously diagnosed arterial hypertension; fasting plasma glucose >100 mg/dl (5.6 mmol/L) or previously diagnosed type 2 diabetes mellitus.

Bilateral baPWV was evaluated by utilizing aBP-203RPE III device ( Omron Healthcare, Kyoto, Japan). Details about this instrument and its use have been described, and clinical validation and good reproducibility have been confirmed [8]. All examinations were carried out by specially trained physicians and nurses. All subjects were light clothing and underwent examination under resting-state by placement of the subject in a supine position without a pillow. Electrodes of the electrocardiograph were located in both wrists, a stethoscope was located in the left border of the sternum for acquiring heart sounds, and cuffs were wrapped with certain strain on both the upper arms and ankles. The lower border of the brachial cuff was located 2–3 cm above the chelidon, and the lower border of ankle cuff was located 1–2 cm above the medial malleolus. Two measured values were recorded from both sides of the body, while the second value of baPWV was utilized. Then we used the higher of the left and right baPWV values for analyses [17].

Arterial stiffness was considered as baPWV ≥1400 cm/s, since this is what has been identified as an independent risk factor in the Framingham score and can distinguish patients with atherosclerotic cardiovascular disease. Diabetes was considered as fasting plasma glucose concentration of ≥7.0 mmol/L or treatment for diabetes with drug or insulin. Hypertension was defined as systolic BP >130 mmHg or diastolic BP >85 mmHg or on drug treatment for hypertension.