This was a multicenter, cross-sectional study which was performed from January 2016 to February 2017 in Korea. We screened consecutive patients aged ≥20 years who were referred to tertiary cardiology or endocrinology clinics to evaluate glucose metabolism, hypertension, or dyslipidemia status in 6 tertiary hospitals (Seoul National University Bundang Hospital, St. Vincent's Hospital of The Catholic University of Korea, Kyung Hee University Hospital at Gangdong, Keimyung University Dongsan Medical Center, Chungnam National University Hospital, and Chungbuk National University Hospital). Among 892 patients who underwent evaluation of RAS components, including PRA and aldosterone levels, we excluded those who were on current usage or previous usage of diuretics, β-blockers, or RAS blockers (such as ACE inhibitors or ARBs) within 12 weeks. Consequently, all enrolled participants were naïve to these agents for at least 12 weeks prior to the evaluation of RAS components. Patients who had type 1 diabetes mellitus (DM) (C-peptide <0.3 pg/mL) or who were receiving insulin therapy were also excluded from the study. We also excluded patients who were suspected of having primary aldosteronism, based on an aldosterone-to-PRA ratio of >30 or the presence of adrenal adenomas shown by imaging tests, and those with active malignancies or medical histories of severe liver or renal disease. Ultimately, 829 patient participants were enrolled after 63 were excluded (Figure 1). The present study was endorsed by the Clinical Study Committee of the Korean Society of Lipid and Atherosclerosis and approved by the institutional review board of Seoul National University Bundang Hospital (IRB-B-1601-332-307) and each study site. This study followed a retrospective design, therefore informed consent was waived by the institutional review board in all institutes.

Height and body weight were measured to the nearest 0.1 cm and 0.1 kg, respectively, while patients were wearing only light clothing and according to standard procedures. Body mass index (BMI) was calculated by dividing weight in kilograms by the square of height in meters. Being overweight and obesity were defined as BMI ≥23 kg/m² and BMI ≥25 kg/m², respectively. Blood pressure was measured with the patient in a sitting position after at least 10 minutes rest using an automated blood pressure monitor at the time the patients visited the clinic. Smoking status was classified as currently smoking or not smoking. Alcohol consumption was assessed by asking the amount and frequency of beer, wine, or spirits intake during the previous 12 months, and a current heavy drinker was defined as someone consuming alcohol 3 times or more per week. Physical exercise was assessed by asking the number of days in which the participant performed moderate physical activity in the past week. Regular exercise was defined as three or more times of exercising for at least 20 minutes. The participants' comorbidities such as DM, hypertension, and dyslipidemia with any history of respective medications were identified through a comprehensive review of medical records. According to the American Diabetes Association 2017 guidelines, DM was defined by a fasting plasma glucose (FPG) concentration ≥126 mg/dL (7 mmol/L), or a level of glycated hemoglobin (HbA1c) ≥6.5%.8) Hypertension was defined according to the guidelines of the Joint National Committee on Detection, Evaluation, and Treatment of High Blood Pressure (systolic blood pressure ≥140 mmHg, diastolic blood pressure ≥90 mmHg, or the use of antihypertensive medication.9) Dyslipidemia was defined as follows: hypercholesterolemia (total cholesterol ≥240 mg/dL), high low-density lipoprotein (LDL)-cholesterol (≥160 mg/dL), low high-density lipoprotein (HDL)-cholesterol (<40 mg/dL), and high triglycerides (≥200 mg/dL) according to the guidelines of the National Cholesterol Education Program and Adult Treatment Panel III (ATP-III).10) Blood samples for the determination of RAS-related hormones, the primary parameters in this study, were drawn after at least 30 minutes of rest in the sitting position. Samples were collected into prechilled EDTA tubes, immediately placed on ice, and centrifuged at 4°C. Plasma was stored at −80°C until analysis. PRA and plasma aldosterone levels were measured by radioimmunoassay using commercial kits (Fujirebio Co., LTD, Tokyo, Japan and Beckman Coulter, Immunotech, Marseille, France, respectively). We adjusted for the site to account for the potential differences in measurement methods of serum aldosterone and PRA by the different institutions. Participants with MetS were identified by the ATP-III and International Diabetes Federation (IDF) criteria.11) The ATP-III guidelines define MetS as when 3 or more of the following components are present: abdominal obesity, serum triglycerides ≥150 mg/dL, HDL-cholesterol <40 mg/dL (men) or <50 mg/dL (women), blood pressure ≥130/85 mmHg, and FPG ≥100 mg/dL (or known DM). Because the IDF suggests ethnic specific values to define central obesity, we used the specific cut-points for the Asian population (waist circumference >90 cm for men and >80 cm for women).12)

In the present study, we used the homeostasis model assessment for insulin resistance (HOMA-IR) and homeostasis model assessment for pancreatic β-cell function (HOMA-β). Quantitative insulin sensitivity check index (QUICKI) were also calculated for evaluating insulin sensitivity.13)14)

The prevalence of MetS in Korea is estimated to be 5.2–31.7% among men and 9.0–40.1% among women.1) The criteria applied for MetS and age range of participants are important factors affecting the incidence of cardiometabolic diseases. In our cohort, we planned to recruit patients aged ≥20 years, so the expected prevalence of MetS would be 15–20% for either sex. We intended to investigate cardiometabolic events such as coronary artery disease, cerebrovascular disease, peripheral arterial occlusive disease, and DM in 3 years. On the assumption of a cardiometabolic event rate of 10% in women and 20% in men for 3 years, we calculated a total of 700 participants to be required for statistical analysis. With a conservative approach and sampling convenience in each site, we planned to recruit around 800 subjects with a 1:1 ratio of men and women in 2015–2016.

Continuous variables are presented as the mean and standard deviation (SD) and categorical variables as counts and percentages. Variables with nonnormal distributions (triglycerides, high-sensitivity C-reactive protein [hsCRP], urinary albumin-to-creatinine ratio, HOMA-IR, HOMA-β, and QUICKI) were logarithmically transformed to achieve a normal distribution. Differences in anthropometric and biochemical variables according to the patient participants' MetS status were evaluated using a Student's t-test. Pearson correlation was analyzed to investigate associations of RAS components with other metabolic parameters. Multiple linear regression analyses were performed to evaluate the associations of MetS components or insulin resistance with various metabolic factors including RAS components. p<0.05 was considered significant. The statistical analyses were performed using IBM SPSS Statistics for Windows (version 21; IBM Corp., Armonk, NY, USA).

The anthropometric and biochemical characteristics of the participants are shown in Table 1. The mean±SD age of study subjects was 52.8±12.8 years and 56.3% were men. The prevalences of type 2 diabetes mellitus (T2DM), hypertension, and dyslipidemia were 50.8%, 38.7%, and 64.3%, respectively. Sixty-three point two percent of participants with diabetes were taking oral hypoglycemic agents, 37.4% of those with hypertension were taking antihypertensive agents, and 53.1% of those with dyslipidemia were taking lipid-lowering agents. The prevalence of MetS was 39.8%. The mean BMI was 25.9±3.8 kg/m². The mean±SD of serum aldosterone, PRA, and aldosterone-to-PRA ratio were 17.5±23.8 ng/dL, 2.5±3.7 ng/mL/h, and 13.7±22.7, respectively.

When the participants were divided into 2 groups according to the presence and absence of MetS, BMI, waist circumferences, blood pressure, lipid profiles, glucose metabolism status, and hsCRP levels were significantly different (Table 2). The participants with MetS were more obese, hypertensive, dyslipidemic, and insulin resistant than those in the control group.

Among the RAS components, the serum aldosterone levels were significantly higher in MetS group than in the control group (20.6±33.6 vs. 15.3±12.2 ng/dL, respectively, p<0.05) (Table 2 and Figure 2 for the mean±SD). However, other components such as PRA or aldosterone-to-PRA ratio were not different between the groups.

In the analysis of the correlation of the RAS activity with metabolic parameters (Table 3), waist circumferences, systolic and diastolic blood pressures, and triglycerides, which are constituents of MetS were positively correlated with serum aldosterone levels (r=0.228, 0.112, 0.108, and 0.181, respectively, all p<0.01). Serum aldosterone levels correlated positively with HbA1c and HOMA-IR (r=0.092 and 0.235, respectively, both p<0.05) and negatively with QUICKI (r=−0.254, p<0.001). In addition, there was a positive correlation of the hsCRP with serum aldosterone levels (r=0.174, p<0.001).

We evaluated whether basic anthropometric and biochemical parameters including RAS components were independently associated with the number of MetS components or insulin resistance parameters. In the multivariable linear regression analysis (Table 4), serum aldosterone level showed positive and independent association with the numbers of MetS components after adjusting for age, sex, total cholesterol, creatinine, alanine aminotransferase, hsCRP, smoking status, alcohol consumption, and exercise habits (p<0.01). In the multivariable regression analysis with HOMA-IR or QUICKI instead of the number of MetS components, aldosterone level was independently associated with these indices. By contrast, other RAS components, such as PRA or aldosterone-to-PRA ratio, were not significantly associated with the number of MetS components or insulin resistance.