Frequently Asked Questions

How do I find out more about NHANES?

1.) What is CDC’s nutrition report?

The National Report on Biochemical Indicators of Diet and Nutrition in the U.S. Population 1999-2002 is a first-of-its-kind report that provides a snapshot of the U.S. population’s nutritional status by age, sex, and race/ethnicity.  It is the first CDC publication that offers information on a wide range of biochemical indicators in a single document.  The goal of the report is to improve our understanding of the levels of biochemical indicators of diet and nutrition in the general U.S. population and in selected sub-populations.

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2.) What information does the report provide?

The report provides comprehensive reference information for 27 biochemical indicators of diet and nutrition found in the blood or urine of people who took part in a national survey conducted by CDC’s National Center for Health Statistics. This survey is called the National Health and Nutrition Examination Survey (NHANES). The report presents data for all or part of the four-year period from 1999 through 2002. For more information about the survey, visit CDC’s NHANES website or download the following CDCfact sheet.

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3.) What information does the report not provide?

While the report covers one important facet in the assessment of nutritional status—biochemical measurements—other aspects, such as anthropometric body measurements, hematologic measurements, clinical signs of nutritional deficiency or excess, and dietary intake, are not covered.

Furthermore, some important micronutrients, such as vitamin C, vitamin B6, and certain minerals (e.g., sodium, potassium, calcium, phosphorus, chloride, magnesium) are not included in this report.  Data were either unavailable for the report years covered or were not representative of micronutrient status.  Future reports may, however, include other biochemical indicators of diet and nutrition.

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4.) What biochemical indicators are included in this report?

CDC measured levels of 27 biochemical indicators for this report.  These indicators, grouped into categories, are as follows:

• Water-soluble vitamins and related biochemical compounds: folate, vitamin B12, homocysteine, methylmalonic acid
• Fat-soluble vitamins and micronutrients: vitamin A, vitamin E, gamma-tocopherol, alpha-carotene, trans-beta-carotene, beta-cryptoxanthine, lutein/zeaxanthin, trans-lycopene, 25-hydroxyvitamin D
• Iron-status indicators: ferritin, iron, total iron-binding capacity, transferrin saturation, protoporphyrin
• Trace elements: iodine and selenium
• Isoflavones and lignans: genistein, daidzein, O-desmethylangolensin, equol, enterodiol, enterolactone

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5.) What is a biochemical indicator?

A biochemical indicator is a compound typically measured in blood or urine.  Biochemical indicators of diet and nutrition are indicative of the nutritional status of a person.  For this report, a biochemical indicator means a vitamin, iron-status indicator, trace element, or other dietary indicator with potential health relevance.  Although most biochemical indicators presented in this report enter the human body from foods or supplements, the body itself produces some indicators in response to dietary intake.

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6.) What statistical information is given for each biochemical indicator in the report?

The nutrition report presents descriptive statistics about the distribution of blood or urine levels of biochemical indicators in the U.S. population.  Statistics include geometric means and selected percentiles with confidence intervals.  Percentiles provide additional information about the shape of the distribution.  The report presents 10th and 90th percentile levels for a biochemical indicator when the sample size was too small for 5th and 95th percentile levels in several subgroups.  Data are presented for the total population as well as by age, sex, and race or ethnicity.

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7.) What methods did CDC use to analyze these biochemical indicators?

To measure these biochemical indicators in blood or urine, CDC’s Environmental Health Laboratory (Division of Laboratory Sciences, National Center for Environmental Health) used a variety of analytical methods: isotope dilution tandem mass spectrometry, gas chromatography coupled to mass spectrometry, inductively coupled plasma mass spectrometry, atomic absorption spectroscopy, high performance liquid chromatography with different detection modes such as UV-visible and fluorescence, and various immuno-, protein binding, and colorimetric assays.  References for these methods can be found in Appendix B of the nutrition report.

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8.) What do these levels of biochemical indicators in people's bodies mean?

Adequate biochemical levels do not necessarily indicate consumption of healthful and balanced diets, as levels can be affected by food fortification and dietary supplements.  On the other hand, differences in biochemical levels between groups do not necessarily suggest health problems.  Independent research is needed to determine levels that indicate risk for disease.

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9.) What are the public health uses of the report?

This report improves our understanding of the levels of biochemical indicators of diet and nutrition in the general U.S. population and in selected subpopulations, such as children, women of childbearing age, and minorities.  The data helps assess inadequate or excess intake and informs analyses on the relation between biochemical indicators and health outcomes.

The report is intended to serve as a resource for nutritionists, clinicians, public health officials, professional associations, and organizations engaged in improving nutritional status and preventing chronic disease.  Publishing this information in a single resource will provide them easy access to critical nutritional data.

Potential public health uses of the information include the following:

• Establishing and improving existing population reference levels that physicians, clinicians, scientists, and public health officials can use to determine whether a person has, or a group of people has, an unusually high or low level of a biochemical indicator.
• Determining whether the nutritional status of special population groups, such as minorities, children, women of childbearing age, or the elderly is different from that of other groups, or whether it needs improvement.
• Tracking, over time, dietary and nutritional trends in the population.
• Assessing the effectiveness of public health efforts to improve the diet and nutritional status of U.S. residents.
• Stimulating research to perform more in-depth analyses of the NHANES data and to generate hypotheses for future nutrition and human health studies.

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10.) What does the report tell us about the state of our nation’s health?

The report does not address the state of our nation’s health.  Rather, it addresses the state of our nation’s nutritional status.  The report covers an important facet in the assessment of the U.S. population’s nutritional status—biochemical measurements—that shows us what the levels of nutritional indicators actually are in people.  The report describes the characteristics of the population and of selected subgroups, but it does not explain why certain groups differ from each other.
 

Observations that indicate adequate biochemical levels do not intend to signify consumption of healthful and balanced diets, as levels can be affected by food fortification and dietary supplements.  Differences in biochemical levels between groups do not necessarily suggest health problems.  Independent research is needed to determine levels that indicate risk for disease.

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11.) What new information does the report provide?

This report is the first CDC publication that offers comprehensive reference data on a wide range of biochemical indicators in a single document.

The data represented in the report comes from CDC’s National Health and Nutrition Examination Survey (NHANES) 1999-2002.  While the data files for these indicators were released several years ago, this is the first time that the data for all available biochemical indicators of diet and nutrition have been processed into tables with detailed demographic reference information.

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12.) Is CDC involved in other studies to determine the relationship between biochemical indicators and health outcomes?

CDC’s Division of Laboratory Sciences collaborates with other federal agencies, academic institutions, governments, and other organizations on several studies of diet and nutrition each year.  Here are some examples of topics the collaborative studies address:

Water-soluble vitamins

• Assessment of changes in folate status as a result of various supplementation regimens in various countries such as China and Honduras
• Relationship between folate, metabolic status, and obesity
• Relationship between folate, diet, DNA repair genes, and cancer
• National Cancer Institute CONCeRN study – a screening study of colorectal adenomas

Fat-soluble micronutrients

• AREDS2 – Lutein/Zeaaxanthin/Omega-3 Supplementation in Persons Over Age 60
• Assessment of vitamin A status as a result of dietary interventions

Isoflavones and lignans (so-called phytoestrogens)

• Breast Cancer Research Centers – Breast cancer and the environment
• LIFE – Determinants of male and female fecundity and fertility: role of environmental hormonally active agents and lifestyle

Multiple biochemical indicators of diet and nutrition

• Nutritional status and recovery of head and neck cancer patients
• Assessment of nutritional status in pregnant women from Peru

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13.) What are other organizations doing to study the relationship between biochemical indicators and health outcomes?

The National Institutes of Health (NIH) sponsor research that addresses nutritional status, its relationship to chronic and infectious diseases, and its interactions with the environment or genes.  For more information, visit the NIH Web site.
 

The Agricultural Research Service (ARS) of the United States Department of Agriculture (USDA) is conducting research in human nutrition and food safety. For more information, visit the USDA Web site.

The Center for Food Safety and Applied Nutrition (CFSAN) at the Food and Drug Administration (FDA) provides consumer information on nutrition and health, food labeling, food safety, and dietary supplements.  For more information, visit the FDA Web site. 

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14.) How can people find out what their levels are for these biochemical indicators?  Can their doctors perform these tests?  If not, can people send samples to CDC or some other laboratory to be tested?

While some of the biochemical indicators listed in the report (such as folate, vitamin B12, homocysteine, 25-hydroxy-vitamin D, and iron-status indicators) can be analyzed in a commercial laboratory at a physician’s request, analyses for most indicators (such as methylmalonic acid, vitamin A, vitamin E, carotenoids, iodine, selenium, and phytoestrogens) are not widely available.

Regardless of the availability of the test, laboratories may use different methods for measuring the indicators reported here.  Different methods may result in different method-specific reference ranges.  Consequently, to apply the results in this report, health science professionals should check with their particular laboratory to be sure their methods compare closely with those used in this report.

CDC does not perform laboratory tests at the request of individuals.

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15.) Will CDC publish future editions of the report?

Pending availability of resources, CDC will publish subsequent editions of the report that may include additional categories of indicators such as omega- and trans-fatty acids, food stimulants such as caffeine and metabolites, and food carcinogens such as acrylamide adducts and aflatoxin-lysine adduct.
 

Over time, the report will:

• Continue to track trends in the biochemical indicators presented in the first report.
• Track trends in new biochemical indicators added to future reports.
• Help assess the effectiveness of public health efforts to improve the diet and nutritional status of U.S. population.

A specific date for construction and release of the next edition has not yet been determined.

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16.) How can I get a copy of the nutrition report?

You can view or download the entire report at www.cdc.gov/nutritionreport.  If you are interested in a printed copy of the report, you may order the report by contacting CDC at 1-800-CDC-INFO or cdcinfo@cdc.gov.

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17.) How do I find out more about NHANES?

Visit the CDC NHANES Website or download the following CDC fact sheet for more information about NHANES.