2.1. Study Population

This was a single center, case-control study. We collected data from 848 consecutive participants who had undergone coronary angiography at the First Affiliated Hospital of China Medical University between 2012 and 2015. This study was approved by the Ethics Committee (Ethic Approval Number: [2011]18 and 2015-68-2). Patients who had at least one vessel with stenosis of no less than 50% diameter were defined as CAD cases (n = 424). Those who had no demonstrable lesions on angiography served as controls (n = 424). The exclusion criteria were as follows: participants with cardiomyopathy, auto-immunological disease, severe kidney or liver disease, or malignant disease.

All participants had their demographic characteristics (e.g., age, sex) recorded and were examined to determine the presence of cardiovascular risk factors. The confounding risk factors were as follows: (a) smoking: individuals who had smoked at least one cigarette per day for more than one year were classified as smokers; (b) alcohol consumption: individuals who had consumed at least one alcoholic drink a day for a minimum period of six months were defined as consumers of alcohol; (c) hypertension: individuals with systolic blood pressure ≥140 mmHg or diastolic blood pressure ≥90 mmHg, or both, were considered hypertensive; (d) hyperglycemia: individuals with fasting plasma glucose ≥7.0 mmol/L or 2-h plasma glucose ≥11.1 mmol/L, or both, were considered hyperglycemic; (e) hyperlipidemia: participants with plasma cholesterol concentration ≥5.17 mmol/L, or plasma triglyceride concentration ≥1.70 mmol/L or plasma low-density lipoprotein cholesterol concentration ≥2.58 mmol/L, were considered hyperlipidemic. Details of the study group characteristics were summarized in Table 1.

Baseline characteristics of the study participants.

Note: H. pylori: Helicobacter pylori.