Ethics statement
The NHANES study protocol received approval from the National Center for Health Statistics Institutional Review Board (IRB). All eligible participants were required to provide informed consent prior to their examination. This adjustment ensures the text is both precise and respectful, in line with contemporary ethical guidelines for research.
Study population
The National Center for Health Statistics, operated by the Centers for Disease Control and Prevention (CDC), conducts the NHANES, which was initiated approximately 60 years ago with the aim of assessing the health and nutritional status of individuals in the United States. The survey encompasses health interviews, conducted in participants' homes, and health examinations, carried out in a mobile examination center (MEC). Data from this survey are made available in online repositories, with updates every two years. The complete NHANES dataset is publicly accessible at https://www.cdc.gov/nchs/nhanes/.
Participants were drawn from the National Health and Nutrition Examination Survey (NHANES) 2013–2014, where a total of 10,175 individuals participated in the interviews. This dataset encompasses demographic, socioeconomic, dietary, and health-related information, providing a comprehensive overview of the participants' health status. Data on AAC were collected for 3,140 participants, among whom details regarding MetS components were noted for 1,841. (Fig. 1)
Metabolic syndrome
MetS is defined by the presence of at least three of the following criteria: hypertension, insulin resistance, hypertriglyceridemia, low HDL cholesterol, or high waist circumference. Hypertension, a criterion of MetS, requires three systolic or diastolic blood pressure measurements to be greater than or equal to 130/85 mmHg or the current use of anti-hypertensive medication. Insulin resistance involves a fasting blood glucose concentration greater than or equal to 100 mg/dL, use of insulin or oral anti-diabetic medication, or a self-reported diabetes diagnosis. A triglyceride concentration greater than or equal to 150 mg/dL characterizes hypertriglyceridemia. For the definition of low HDL-C, levels must be less than 50 mg/dL for women and less than 40 mg/dL for men. A waist circumference greater than 88 cm for women and greater than 102 cm for men defines high waist circumference.[7].
AAC evaluation
AAC scores were determined via lateral lumbar (vertebrae L1-L4) dual-energy X-ray absorptiometry (DXA), employing the Kauppila score system. [8], Calcification extent of both the anterior and posterior aortic walls was assessed at each vertebral level (L1-L4) on a scale from 0 to 3. AAC was defined as a total score greater than 0, and severe AAC as a score above 6, indicating significant AAC, consistent with prior research.[9].
Covariates Assessment
The study incorporated a comprehensive array of covariates, including demographic factors (age, sex, race/ethnicity, marital status, education level), socioeconomic status (family poverty income ratio [PIR]), health behaviors (smoking status, alcohol consumption status), physical measurements (body mass index [BMI], waist circumference), and biochemical markers (hemoglobin [Hb], fasting glucose [FBG], glycohemoglobin [HbA1c], aspartate aminotransferase [AST], alanine aminotransferase [ALT], serum creatinine [Scr], serum phosphorus, calcium, total cholesterol [TC], triglycerides [TG], high-density lipoprotein cholesterol [HDL-C]). During home interviews, participants self-reported data on age, sex, race/ethnicity, marital status, education level, smoking status, and alcohol consumption status. Trained interviewers employed computer-assisted personal interviewing techniques to collect demographic information. Age was classified into two categories: 40 to 60 years and over 60 years. Race and ethnicity were divided into five categories: Mexican American, Non-Hispanic White, Non-Hispanic Black, Other Hispanic, and Other Race. PIR was calculated by dividing the monthly family income by the poverty threshold, subsequently classified into three groups: ≤1.30, 1.31 to 3.50, and ≥ 3.50. Education levels were segmented into three categories: less than high school, high school graduate, and more than high school. Marital status was categorized into two groups: single/separated and in a partnership. Additionally, laboratory tests provided data on Hb, FBG, AST, ALT, Scr, serum phosphorus, calcium, TC, TG, and HDL-C. Detailed descriptions of the research variables are accessible at https://www.cdc.gov/nchs/nhanes/.
Statistical analysis
Analyses were conducted using Empower software and R version 3.4.3, accounting for NHANES's complex sampling methods. Observations were weighted to reflect the general U.S. population, using calculations by the National Center for Health Statistics. These weights also adjusted for non-response biases.
Continuous variables were represented as means and standard deviations (SDs), while categorical data were expressed in numbers and percentages. Group differences were assessed using the χ2 test for categorical and Student's t-test for continuous data. Logistic regression models assessed the association between MetS, AAC, and severe AAC prevalence. For ANCOVA, three models were constructed: 1) Unadjusted; 2) Adjusted for gender, age, and race; 3) Further adjusted to include BMI, smoking status, alcohol use, calcium, phosphorus, 25OHD2. A p-value of < 0.05 was considered statistically significant for all analyses.