National Health and Nutrition Examination Survey (NHANES) 1999-2000

The National Health and Nutrition Examination Survey (NHANES) is conducted by the National Center for Health Statistics (NCHS), Centers for Disease Control and Prevention. NHANES is designed to collect data on the health and nutritional status of a statistically representative sample of the noninstitutionalized, civilian U.S. population.
The five major goals of NHANES are to provide:

1. national population reference distributions of selected health parameters (e.g., height, weight);
2. national prevalence data on diseases, functional impairment, and risk factors (e.g., heart and respiratory diseases, smoking, exposure to environmental pollutants);
3. information on secular changes in selected diseases and risk factors;
4. information to help understand disease etiology; and
5. information for investigating the natural history of selected diseases.

Background

Over the years, NHANES data have been used to support public health policy with the goal of improving the health and nutritional status of the U.S. population. A few of the more notable examples include the use of NHANES data to:

1. develop growth charts that are used nationally and internationally to assess the growth of children;
2. assess vitamin and mineral intake of the population to improve our diets (e.g., iron deficiency in diets was discovered, leading the government to require fortification of grains and cereals with iron);
3. track cholesterol levels in adults, thereby helping establish the link between high cholesterol and the risk of heart disease; and
4. provide evidence to Congress on the levels of lead in blood, particularly in children, which in the past led to the ban on lead additives in gasoline and the elimination of lead from solder in food and drink cans.

All NHANES are cross-sectional surveys, conducted in a similar manner; and contain a core set of questions, physical examinations, and physiological tests. Blood and urine are collected from all subjects and tested for a variety materials, including micronutrients, markers for certain diseases, and environmental pollutants. Information is also collected about diseases and health status, diet, sociodemographics, occupation, and education. All data are collected through household interviews and laboratory examinations conducted in mobile examination centers (MEC).

In addition to the core elements, each survey contains other components requested by various federal agencies that help plan and fund the survey. A significant change to the survey content was started with NHANES99-00 (conducted from 1999-2000) and will continue into the future. This change includes the testing of blood and urine for an extensive number of chemicals that are of public health concern. In past surveys a very limited number of chemicals (e.g., lead, cadmium) were tested. A now greatly expanded list of chemicals includes dioxins, furans, PCBs, pesticides, and pesticide metabolites (i.e., breakdown products), volatile organic compounds, heavy metals, plant estrogens, polyaromatic hydrocarbons, and markers for tobacco smoke. The list of specific chemicals will change in the future, as the needs of funding agencies change in response to public health concerns. Because of the complex design of NHANES, caution must be exercised when evaluating the data. Users must read the data file documentation before undertaking any analysis in order to understand details of the survey that could have significant impact on their results. For example, the use of sampling weights is recommended for all analyses because the sample design incorporates differential probabilities of selection of subjects into the survey. In addition, while many of the tests and questions are administered to all subjects, there are certain components and laboratory analyses that are performed on only a subsample (e.g., one-third or one-fourth) of all individuals. This subsampling must be accounted for in all analyses.

History

• 1956 The National Health Survey Act provides the legislation authorizing establishment of a continuous survey to provide current statistical data on the amount, distribution, and effects of illness and disability in the U.S. Since passage of this Act, NCHS has conducted seven major surveys, resulting in extensive, publicly available data on health effects, nutrition, and to a more limited extent, environmental exposures, from statistically representative samples of the U.S. population.
• 1960 - 1970 Three National Health Examination Surveys (NHES) were conducted to collect data on chronic diseases in adults (NHES-I) and data on growth and development of children (NHES- I & II).
• 1970's In the early 1970s, with discovery of the link between nutrition and certain diseases, NHES was expanded to include collection of nutritional information, and the survey was renamed the National Health and Nutrition Examination Survey.
• 1971 - 1994 Since 1971, there have been four discrete surveys:
  • NHANES-I (1971-75),
  • NHANES-II (1976-80),
  • Hispanic HANES (1982-84), and
  • NHANES-III (1988-94).
• 1999 In the spring of 1999, NHANES was changed into a continuously operating survey, collecting data on roughly 7,000 to 10,000 individuals annually.

Other Sources:

For additional details, visit the NHANES 1999-2000 data release page at http://www.cdc.gov/nchs/about/major/nhanes/NHANES99_00.htm. For information on the sample design, weighting, and variance estimation methodology, review the NHANES 1999-2000 analytic guidelines at http://www.cdc.gov/nchs/data/nhanes/guidelines1.pdf.

Additional Information