Methods

The NHANES is a stratified multistage probability sample of the civilian noninstitutionalized population of the United States conducted by the National Center for Health Statistics, Centers for Disease Control and Prevention. Participants completed a detailed home survey on demographic, socioeconomic, and health interview data followed by a physical examination and laboratory measurements in mobile health centers. Beginning in 1999, the survey was conducted continuously and released in 2-year cycles. The NHANES oversamples members of ethnic and racial minorities including African-Americans and Mexican-Americans. For our study, we merged data from 1999 through 2008 to provide an adequate sample size. The final study sample totaled an unweighted population of 11,858 Hispanic adults >20 years old.

Using NHANES data from 1999 through 2008, we assessed degree of acculturation in Hispanics based on language using the Short Acculturation Scale (SAS), a previously validated 5-item Spanish-language usage scale with good internal reliability (Cronbach coefficient alpha ≥0.90). These 5 questions are (1) In general, in what language do you read and speak? (2) What was the language(s) that you used as a child? (3) What language(s) do you usually speak at home? (4) In what language(s) do you usually think? (5) What language(s) do you usually speak with your friends? Each question could be answered as 1 (only Spanish), 2 (more Spanish than English), 3 (equal English and Spanish), 4 (more English than Spanish), or 5 (only English). The SAS scores ranged from 5 to 25, with lower scores representing a lower degree of acculturation. We dichotomized subjects with scores ≤15 as low acculturation and scores >15 as moderate to high acculturation, as in previous studies.

Years of residency in the United States has been used in previous studies as a measurement of acculturation in foreign-born Hispanics. We grouped our results into categories (<5, 5 to 10, 10 to 15, 15 to 20, and >20 years) for ease of interpretation.

Collection, storage, and management of blood samples are described on the NHANES Web site. Nonfasting blood samples were collected in adults, centrifuged within 1 hour of phlebotomy, and frozen at −10°C. CRP concentration in serum was measured by a high-sensitivity assay using latex-enhanced nephelometry, with a lower limit of detection of the assay of 0.1 mg/L. The performance of this test has been well-validated. High-sensitivity CRP levels were categorized into 3 clinically relevant categories: <1 mg/L as low risk for future cardiovascular events, 1 to 3 mg/L as intermediate risk, and levels >3 mg/L as high risk.

Participants were asked to self-report race and ethnicity. Hispanics were categorized as Mexican-American or other Hispanic. We grouped Mexican-American and other Hispanic into 1 category. We included demographic variables of gender (man or woman) and age (20 to 39, 40 to 60, or >60 years). Financial status was categorized using the poverty income ratio, in which family income is divided by the federally defined poverty threshold for that family (poverty income ratio <1 indicates impoverishment). Low educational attainment was defined by noncompletion of 12th grade. Insurance status was defined as medical coverage provided by Medicare, Medicaid, private sources (including government and single-service insurance), or having no insurance. We also noted if participants reported having a usual place of care (yes/no) and if they had United States citizenship (yes/no).

We adjusted for several important clinical covariates that may have mediated or confounded the relation between acculturation and CRP. Diabetes was defined as self-report of a physician diagnosis or as current or previous use of insulin or an oral hypoglycemic agent. We excluded diabetes diagnoses made during pregnancy. History of cardiovascular disease included congestive heart failure, coronary artery disease, angina, myocardial infarction, and stroke. Subjects were considered to have hypertension if they reported a physician diagnosis of hypertension, took antihypertensive medications, or if they had ≥2 separate blood pressure readings where the systolic blood pressure was ≥140 mm Hg and/or diastolic blood pressure was ≥90 mm Hg. Hypercholesterolemia was defined as a reported physician diagnosis of hypercholesterolemia or if the subject reported taking prescription medications for high cholesterol. Body mass index (BMI) was calculated as weight in kilograms divided by height squared (normal <25 kg/m ² , overweight 25 to 29 kg/m ² , obese ≥30 kg/m ² ). We controlled for smoking status (current, previous, never), estrogen use (limited to women, yes/no), and statin use (yes/no).

We used SAS 9.2 for Windows (SAS Institute, Cary, North Carolina) and SUDAAN 10 (Research Triangle Institute, Research Triangle Park, North Carolina) to account for design effect, sample weights, and clustering of the complex NHANES sample design. All Hispanic adults >20 years of age were included in the analyses but participants with CRP levels >10 mg/L were excluded because this typically signifies acute illness.

Descriptive data are presented as weighted proportions. We used chi-square test to compare the distribution of participants’ demographic and clinical characteristics. We then constructed multivariate linear regression models with CRP level as the main response variable. Because CRP levels are not normally distributed, we transformed CRP levels into a logarithmic scale. All demographic and clinical predictors were included in the final model. For ease of interpretation, beta coefficients from the linear regression models were back-transformed into a relative difference (RD). An RD can be interpreted as percent change (higher or lower) in CRP levels for every unit change of the predictor variable. All reported p values are 2-tailed and values <0.05 were considered statistically significant.