National Health and Nutrition Examination Survey IV (NHANES (IV)

BACKGROUND:

The first National Health and Nutrition Examination Survey (NHANES I) was conducted by the National Center for Health Statistics between 1971 and 1974. NHANES I was a clustered, multi-stage stratified probability sample of 23,808 individuals ranging in age from one to 74 years and drawn from the non-institutionalized civilian population of the United States. A random subsample of the 14,407 examined adults aged 25-74 were given supplemental questionnaires on cardiovascular and respiratory history.

In 1981, the National Institute on Aging and the NCHS began a follow-up of the original NHANES I cohort. In order to evaluate the usefulness of major epidemiological studies for predicting coronary heart disease in the United States population, the NHLBI added a Framingham model verification component to the follow-up. The risk factors (systolic blood pressure, serum cholesterol, and cigarette smoking) for death from coronary heart disease were compared using results from the seventh cohort examination of 1960-1964 as baseline in Framingham and the NHANES I examination of 1971-1974 as baseline for the NHANES I Epidemiologic Follow-up Study (NHEFS). The endpoint for each study was coronary heart disease death as coded from the death certificates. Results of the NHLBI portion of the follow-up demonstrated that the major risk factors for coronary heart disease mortality described in previous Framingham analyses were applicable to the United States white adult population.

In 1986, the total surviving cohort of NHANES I (approximately 12,500) were re-contacted in order to improve risk factor morbidity and mortality analyses. The NHLBI contributed to funding the NHANES III and currently contributes to funding NHANES IV. NHANES III incorporated features which distinguished it from earlier surveys in the series. The features included a longitudinal component, meaning that individuals were followed over time for vital statistics and re-examination, long-term biological specimen banking, and oversampling of Blacks and Hispanics. The component of additional questions and procedures provided information on the common heart, vascular, lung, and blood diseases, risk factors and elements of medical care. It also indicated how representative the NHLBI population-based epidemiologic studies were and to what extent the findings of these studies could be generalized to the United States population. The major NHLBI ongoing studies which were compared with NHANES III were the Coronary Heart Disease Risk Factor Development in Young Adults (CARDIA), Atherosclerosis Risk in Communities (ARIC), the Framingham Heart Study, and the Cardiovascular Health Study.

Field work for NHANES III began in September 1988. The first wave of data collection was completed from 1989 to 1991. The second wave of data collection was carried out from 1992 to 1994. ECG data were released to the public in 1998.

DESIGN NARRATIVE:

Beginning in 1981, NHLBI supplemented the NHANES examination protocol by including questions about history of heart, lung, and blood diseases, and their treatment. The examination also included the Rose questionnaires for angina, myocardial infarction and peripheral vascular disease, 12-lead electrocardiograms, questions about known and suspected risk factors including active and passive smoking, weight history, use of exogenous hormones, family history of heart, lung and blood diseases, and selected aspects of diet, psychosocial characteristics (depression, anxiety, social support, job control and demands, and anger experience and expression), and lifestyle. If feasible, 2-hour ECG Holter monitor records were obtained to identify and classify premature ventricular contractions and to detect episodes of ischemia. Pulmonary function tests were performed using standardized methods and strict quality assurance procedures and the American Thoracic Society-Division of Lung Diseases respiratory disease questionnaires were administered. Waist and hip girth measurements were obtained along with other anthropometric measures. Blood pressure determinations were made in the home as well as in the mobile examination center. Blood tests included lipids and lipoproteins, fibrinogen, hematocrit, white blood cell count, and differentials, fasting and post-challenge insulin and glucose concentrations, and nutritional biochemistries.

The NHLBI is currently supporting part of NHANES IV. NHANES IV is a study of a representative sample of approximately 30,000 of the non-institutionalized population of the United States, obtained through the use of a complex multi-stage sampling design using a combination of health questionnaire and physical exam. Each single year and any combination of consecutive years comprises a nationally representative sample which will facilitate linkage to other surveys that provide yearly estimates such as the Continuing Survey of Food Intake by Individuals and allow limited national estimates from NHANES IV each year. The NHLBI component obtains information on the prevalence and distribution of common heart, vascular, pulmonary and blood diseases. The core questionnaire is based on the Health Interview Survey (HIS), and provides information on disease, risk factors, and components of medical care. Through the use of a Mobile Exam Center (MEC), subjects throughout the country are administered a standardized physical exam to obtain data on blood pressure, venipuncture, spirometry, congestive heart failure (CHF), and ankle-arm blood pressures. Sub-populations of the U.S. of particular interest, including minorities and age groups of particular concern like the very young and the elderly, will be over-sampled. Specific objectives of NHANES IV include: ascertaining the prevalence of common heart, vascular, lung, and blood disease in a representative sample of the non-institutionalized population of the United States; estimating the frequency and distribution of known and suspected risk factors for these heart, vascular, lung, and blood disease; measuring associations between risk factors and diseases; ascertaining the frequency and distribution of medical, surgical, pharmacologic, and behavioral interventions used to prevent or treat heart, lung and blood diseases; measuring trends over time in heart, lung and blood diseases and risk factors; relating clinically manifest disease, risk factors, and components of medical care detected at the baseline examination to subsequent morbidity and mortality (detected by follow-up questionnaires and matching with the National Death Index); determining the extent to which findings in NHLBI populations-based epidemiological studies reflect national data and may be generalized to the U.S. population. A Central Lipid Laboratory will be established to: standardize for lipid measurements; accurately measure total cholesterol and HDL cholesterol for the entire NHANES IV sample population; and accurately measure triglycerides for the fasting NHANES IV population.

Phase I data from the first three years of the study were made available in June, 2002. Phase II data from NHANES IV became available in May, 2004.