NHANES: 50 Years of Health Measures and Their Contributions to Public Policy
The National Health and Nutrition Examination Survey (NHANES) recently celebrated 50 years of providing data to inform public health policy in the United States.
NHANES is a unique survey, in that sampled participants come to a mobile medical examination center to have standardized physical and clinical measurements, including blood and urine samples, taken. The goal of the survey is to supplement self-reported household interview data with actual and precise clinical measurements to better assess health and nutritional status.
As one major example, the body mass index (BMI) is often used when examining overweight and obesity and their relation to health. NHANES takes standardized measurements of height and weight and uses those measures to accurately determine BMI. Comparing the actual measures to self-reported height and weight in interviews demonstrates the bias in self-reported values.
In addition to providing more accurate information about health status, laboratory measures in NHANES can supply information on undiagnosed conditions. This is especially important for medical conditions such as diabetes. NHANES fasting blood samples allow the number of Americans who are either undiagnosed diabetics or “pre-diabetic” to be estimated based on impaired glucose tolerance. Determining the number of people in the country with undiagnosed conditions helps policymakers better understand the magnitude of the problem and target those who are at increased risk for inclusion in public health intervention programs.
The information on undiagnosed conditions can be used with the rich database in NHANES to monitor the effect of changes in public health policy. As an example, the data on individuals with excess cholesterol levels can be combined with the dietary intake data to give a more complete picture of the extent and possible sources of this major health problem. In terms of tracking over time, the NHANES laboratory measures can be used in conjunction with the dietary interview data to demonstrate that the decline in total cholesterol between 1976 and 2000 paralleled the decreased dietary fat intake recommended by the National Cholesterol Education Program and the Dietary Guidelines for Americans.
While the early NHANES surveys collected many important health measures, the survey has expanded over the years to include new survey components that reflect the data needs for new and emerging public health issues. A major nutrition component was added to NHANES in 1971. In 2002, the Department of Health and Human Services and U.S. Department of Agriculture integrated their two primary dietary intake surveys (NHANES and CSFII) to create the “What We Eat in America” component of the NHANES survey. At this time, NHANES is the only national nutrition survey with extensive dietary intake data and nutrition biomarkers; it serves as the cornerstone of the National Nutrition Monitoring Program.
Another example of impact in the nutrition area has been the monitoring of folate levels. Adequate levels of folate are needed by women who become pregnant to prevent birth defects such as neural tube defects and Spina Bifida. Early NHANES data showed relatively low levels of serum folate in the U.S. population. These data, along with data from randomized clinical trials, led to the decision to fortify the food supply with folic acid. More recent NHANES data have shown that these changes in food fortification policy have resulted in higher blood folate levels in the population. Comparison to vital statistics data shows the increase in folate levels correlates with the observed decrease in certain birth defects.
Using the blood and urine samples, a major environmental exposures assessment has been ongoing since 1999, with the number of chemicals monitored growing from a dozen to more than 200. Earlier surveys had a limited number of environmental exposures. The most important was the assessment of blood lead levels in the U.S. population, which provided critical data that led to legislation to remove lead from gasoline.
A second early example involved the monitoring of mercury levels and their relation to fish consumption patterns. The effect of changes in smoking laws is monitored through the measurement of serum cotinine. Other environmental exposure assessment of significant impact includes the monitoring of levels of Bisphenyl-A, perchlorate, pesticides, and volatile organic compounds.
The data collected by NHANES, along with data from other NCHS data systems, provide a more complete picture of the nation’s health. The National Center for Health Statistics (NCHS) will celebrate its 50th anniversary this year. The National Health Interview Survey and NHANES were fielded before NCHS was formally constituted, and the first provider survey started in 1965. As NHANES has grown to meet changing data needs, so have all of NCHS’s data systems, and these systems will continue to innovate to meet future needs.
A more complete listing of the various data collected in NHANES appears on its website.