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National Center for Health Statistics, Centers for Disease Control and Prevention, Hyattsville, MD 20782
2To whom correspondence should be addressed. E-mail: kradimer{at}cdc.gov.
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ABSTRACT |
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 TOP ABSTRACT Current procedures for dietary...Challenges in monitoring dietary...SummaryLITERATURE CITED |
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KEY WORDS: • dietary supplements • monitoring • measurement • NHANES • NHIS • CSFII
Three large nationally representative surveys relating to health or nutrition in the United States—the National Health and Nutrition Examination Survey (NHANES) (1–3), the National Health Interview Survey (NHIS) (4,5) and the Continuing Survey of Food Intake by Individuals (CSFII) (6)—have included questions about dietary supplement use since the early 1970s. Table 1 presents the specific questions and response choices relating to dietary supplements that these surveys have used. Tables 2345 present results from these surveys that have been published in journals or on the Internet.
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Additional analyses of these data are warranted to provide further monitoring of dietary supplement use in women. These could involve more in-depth analysis of the dietary supplement use itself as well as analyses in relation to other measures such as health conditions, health-related behaviors, dietary intake, food program participation, dietary beliefs and knowledge and demographics.
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Current procedures for dietary supplement data collection and release in NHANES |
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TOPABSTRACTCurrent procedures for dietary...Challenges in monitoring dietary...SummaryLITERATURE CITED |
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NHANES collects data on health and nutrition from a nationally representative sample of noninstitutionalized civilians of all ages living in the United States. The survey is conducted by the National Center for Health Statistics (NCHS), which is part of the Centers for Disease Control and Prevention. Selected population groups of particular interest are oversampled; these groups include people with low incomes, African Americans, Mexican Americans, adolescents, the elderly and pregnant women. Approximately 5000 people are surveyed per year, drawn from 12 to 15 communities. Previous NHANES were periodic surveys, but since 1999, NHANES has been continuously in the field and now is referenced by year rather than by a Roman numeral, as was done in the past. Data are released to the public after data cleaning, editing and removal of all identifying information so that the confidentiality of participants is ensured. Data are expected to be released in 2-y cycles (i.e., NHANES 1999–2000, 2001–2002, etc.).
NHANES data are collected both in the participants’ homes and in the NHANES mobile examinations centers. The household interview includes questions about the individual participants, their family and their household. Specifically, the interview includes questions about the participant’s history of health conditions, socioeconomic status, environmental and occupation exposures and health behaviors (such as alcohol and tobacco use; weight history; physical activity; social support; and use of pain relievers, antacids, prescription medication and dietary supplements). Measurements taken in the mobile examination centers include those relating to cardiovascular disease, diabetes, respiratory and kidney diseases, physical fitness, vision, hearing, balance, bone health, mental health, cognitive functioning, endocrine disrupter exposure, dietary intake, nutritional biochemistries and hematology, blood lipids, anthropometry and body composition.
Dietary supplement data collection in NHANES.
In the household interview, participants are asked whether they have taken any vitamins, minerals or other dietary supplements in the last month. If so, the interviewer requests to see the supplement containers. Because of their calcium content, the use of antacids is also queried. Interviewers record the name of the dietary supplement, check whether it is on the list of supplements available on their pentop computers, and select a match if one is found. They also record the name and address of the manufacturer, distributor or retailer, depending on what is on the label. Strength information is recorded for selected single-ingredient products. If the container is not seen, the interviewer asks the participant for the name or at least the type of product. Participants are also asked how long they have been taking this product or a similar product, on how many days they took it in the last month and how much they usually took on a single day.
Database development.
NCHS attempts to obtain label information for each supplement reported by a participant. The method of choice is to obtain a copy of the label directly from the manufacturer, distributor or retailer. If this is unsuccessful, the label information may be obtained via the Internet, catalogs, the Physician’s Desk Reference or other databases.
Information from the label or substitute information source is entered into the NHANES dietary supplement database. This includes the product name, ingredient names and amounts that are inside the facts box, the serving size and the recommended dosage. The database also includes the source of the information (e.g., label, Internet, catalogue, etc.) and categorizations of the supplement made at NCHS.
Data release.
To prepare data for release to the public, a supplement name reported by the participant is matched to the one in the NHANES database when this match is exact or very close. If there is no match and all the product’s ingredient strengths are known from the product’s name, the reported product is matched to a generic product of the same strength (e.g., vitamin C 500 mg, without a brand). If all strengths are not known, the reported product may be matched to a default product that is selected based on sales data or analyses of NHANES data where possible. If these are not available, the reported product will be matched to a similarly named product manufactured by a large private-label-brand manufacturer, if possible. For exact, close, generic and default matches, the product’s name, ingredients and amounts, serving size and recommended dosage will be released. In cases where no such match can be made, only the name of the product will be released, which can still be useful for product categorization. For all reported products, information on the duration, frequency and amount of the product taken and whether the container was seen will also be released.
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Challenges in monitoring dietary supplement use |
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TOPABSTRACTCurrent procedures for dietary...Challenges in monitoring dietary...SummaryLITERATURE CITED |
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As seen in Table 1, the three nationally representative surveys that have collected data on dietary supplement use have not used similar methods. Differences include the implicit or explicit definition of a dietary supplement, reference time frame, definition of a supplement user, level of detail collected about supplement use and the supplement itself.
Some of the differences may result from the need to achieve comparability between assessment of dietary supplement use and other components of a survey. For example, in NHANES, many questions in other parts of the survey refer to the last 30 d, some of the biochemical parameters reflect fairly short-term conditions and dietary intake is measured using the 24-h recall method. For compatibility and because accuracy of reporting may decrease with an increasing time frame, NHANES now specifically asks about supplement use in the last 30 d.
Other differences in the level of detail or types of supplements queried may be related to the goals of a particular survey. For example, NHIS has usually asked about dietary supplement intake as part of a periodic supplementary cancer questionnaire funded by the National Cancer Institute that is appended to the core survey. The supplement types included are some of those that have been of particular interest for cancer prevention.
Other differences may relate to the respondent time burden or the expense of dietary supplement data collection. For example, CSFII is primarily a diet and nutrition survey. Ideally it would have included exact ingredient amounts for all supplements containing vitamins or minerals so that these amounts could be combined with dietary data to derive total nutrient intake. However, this type of data collection is expensive and time consuming. Perhaps in consideration of these constraints, only nonquantified information on a limited number of supplement types were included in CSFII.
Differences over time within the same survey may have emanated from increased experience in asking about dietary supplements, heightened interest in dietary supplement use, the proliferation in types of supplements and the increase in their use. For example, the need for a reference time frame in the question is now clearly apparent as is the frequency with which supplements are taken and the length of time they have been taken. Between-survey differences may have resulted from an initial lack of coordination in deriving a standard set of questions to be used in all surveys. Increased consistency between surveys is becoming more common, and for dietary supplements, the leadership of the Office of Dietary Supplements at the National Institutes of Health has been particularly helpful in gathering academic and government researchers to share experiences and information. An interagency working group may be particularly useful in this regard.
Lack of comparability in survey data analysis.
Some of the differences in data presentation seen in Table 2 do not result from data collection differences but from differences in the analyses undertaken. Reanalysis of previous surveys using common age groupings and similar categorization of supplements will allow more informative comparisons over time than those available with currently published findings.
Determination of what products are dietary supplements.
The Dietary Supplement Health and Education Act of 1994 defined a dietary supplement as "1) .. a product (other than tobacco) intended to supplement the diet that bears or contains one or more of the following dietary ingredients; a) a vitamin; b) a mineral; c) an herb or other botanical; d) an amino acid; e) a dietary substance for use by man to supplement the diet by increasing the total dietary intake.. (b)is not represented for use as a conventional food or as a sole item of a meal or the diet, and (c) is labeled as a dietary supplement.." (15). Even with this definition, it may be difficult to determine definitively whether a specific product is a dietary supplement. For example, sports-oriented drinks and powders may be consumed simply as drinks or taken specifically to improve athletic performance or to aid recovery from athletic activity. No major national survey has asked how a product is used by the participant, thus categorization cannot be made on this basis. Are such products to be considered dietary supplements?
Similarly, many people ingest botanical supplements in capsule form. Some may use the contents of the capsule to make a tea or may purchase a tea made of this same botanical ingredient. Is the one in capsule form a dietary supplement and the same product dissolved in hot water a food rather than a supplement?
Homeopathic medicines often contain botanical products, products made from glandular material and other products that are also found in dietary supplements, but the ingredient amounts may be listed differently (e.g., in percentages, with dilution factors or in other manners unfamiliar to many nutritionists). Despite similarities in some ingredients and some purposes, especially because dietary supplements are often used for disease prevention or cure or to maintain health (16), the differences in labeling suggest that homeopathic medicines should not be considered dietary supplements. Nonetheless, survey respondents may include these when asked whether they take any dietary supplements.
Simplification of data collection on dietary supplements.
The current NHANES procedures relating to dietary supplement data collection require substantial staff, time and expense. Interviewers must be trained to collect sufficiently detailed information to adequately identify the product. Interviewer time in the household to collect this information can be lengthy. Staff at NCHS must monitor incoming data; locate manufacturers and request labels, which often requires multiple contacts; peruse alternative information sources; enter information into the database; and match reported products to known products. Computer support is considerable for the programming and maintenance of data collection, data transfer, picklist updating, database development and modification, data coding and data release.
It is not clear that the level of precision and detail on dietary supplements currently collected in NHANES is required or used by researchers and policymakers. As can be seen in Table 1, other surveys generally have not collected comparable levels of detail on dietary supplements. A potential simplification in data collection in NHANES would be to list individual vitamins, minerals, botanicals and amino acids as well as a variety of multiple-ingredient products and have interviewers select these products from a list. Default strengths would be added for data release. Other product types could either be left unspecified or label information could be collected on these.
There are a number of drawbacks to such a simplified system of data collection. At a practical level, it may be difficult to assign defaults for single-ingredient products. Industry data on this are not readily available. Sales data are available for some multiple-ingredient products, such as multivitamin-mineral combinations, and so could be used to assign default products but are not readily available for best-selling strengths of single-ingredient products. Complicating the assignment of defaults is the increasing variety of multiple-ingredient products named for specific groups or health concerns (e.g., senior, men’s, women’s, stress, cardiac formula) and of multivitamin-mineral products with other ingredients (e.g., botanicals). However this issue is not too dissimilar to that encountered in constructing a foods database, especially for use with a food frequency instrument, and some precise data collection on exact supplements taken could be used to guide default assignment.
A more important drawback is the imprecision in ingredient strengths assigned to a participant compared with what was actually taken by that person. Such precision is particularly important for vitamins and minerals, for which Recommended Dietary Intakes exist and physiological roles are known. It may be less important for botanicals, for which dosages to achieve specified physiological purposes are generally not well established. Although rigorous precision may not be necessary in estimating intake at a population level, monitoring of the prevalence of intake excesses as well as deficiencies could be more greatly compromised by the use of default values.
The main advantage of such a system would be the enormous time and cost savings. Although the strengths of ingredients would be less precise, nutrient content of foods may also vary enormously, particularly for natural products, such as the amount of vitamin C in an orange. Thus, the level of imprecision arising from more generically collected data may not be out of line with that of many foods. Given recent evidence that supplement labels may not accurately reflect actual supplement content for both nutrient and nonnutrient ingredients (17), the apparent precision assumed when using exact label values for product ingredients may, in fact, not be as great as has been assumed. Given the currently limited funds available for national nutrition and health surveys, a more expeditious if less precise dietary supplement data collection and release procedure may need to be considered.
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Summary |
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TOPABSTRACTCurrent procedures for dietary...Challenges in monitoring dietary...SummaryLITERATURE CITED |
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FOOTNOTES |
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3 Abbreviation used: CSFII, Continuing Survey of Food Intakes by Individuals; NCHS, National Center for Health Statistics; NHANES, National Health and Nutrition Examination Survey; NHIS, National Health Interview Survey.
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LITERATURE CITED |
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TOPABSTRACTCurrent procedures for dietary...Challenges in monitoring dietary...SummaryLITERATURE CITED |
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1. National Center for Health Statistics (1977) Plan and operation of the Health and Nutrition Examination Survey, United States 1971–1973. Vital Health Stat 1(2b):21.
2. National Center for Health Statistics (1981) Plan and operation of the Second National Health and Nutrition Examination Survey, 1976–80. Vital Health Stat 1(15):115.
3. National Center for Health Statistics (1994) Plan and operation of the Third National Health and Nutrition Examination Survey, 1988–94. Vital Health Stat 1(32):166-169.
4. National Center for Health Statistics (1987) Current estimates from the National Health Interview Survey, United States 1986. Vital Health Stat 10(164):175-176.
5. National Center for Health Statistics (1993) Questionnaires from the National Health Interview Survey, 1985–89. Vital Health Stat 1(31):114-115.
6. United States Dept of Agriculture () Survey Questionnaires, Day 1 Available at http://www.barc.usda.gov/bhnrc/foodsurvey/Questionnaires.html. Accessed May 2002.
7. Block, G., Cox, C., Madans, J., Schreiber, G. B., Licitra, L. & Melia, N. (1988) Vitamin supplement use, by demographic characteristics. Am. J. Epidemiol. 127:297-309.
8. Koplan, J. P., Annest, J. L., Layde, P. M. & Rubin, G. L. (1986) Nutrient intake and supplementation in the United States (NHANES II). Am. J. Public Health. 76:287-289.
9. Moss, A. J., Levy, A. S., Kim, I. & Park, Y. K. (1989) Use of vitamin and mineral supplements in the United States: current users, types of products, and nutrients. Advance data from vital and health statistics; no 174 1989 National Center for Health Statistics Hyattsville MD .
10. Subar, A. F. & Block, G. (1990) Use of vitamin and mineral supplements: demographics and amounts of nutrients consumed; the 1987 Health Interview Survey. Am. J. Epidemiol. 132:1091-1101.
11. Slesinski, M. J., Subar, A. F. & Kahle, L. L. (1995) Trends in use of vitamin and mineral supplements in the United States: the 1987 and 1992 National Health Interview Surveys. J. Am. Diet. Assoc. 95:921-923.[Medline]
12. U. S. Department of Agriculture () Table set 12: Supplementary data tables: 1994–96 CSFII. Table sets in PDF format Available at http://www.barc.usda.gov/bhnrc/foodsurvey/Products9496.html#table. Accessed May 2002.
13. Ervin, R. B., Wright, J. D. & Kennedy-Stephenson, J. (1999) Use of dietary supplements in the United States, 1988–94. National Center for Health Statistics. Vital Health Stat. 11(244).
14. Radimer, K. L., Subar, A. F. & Thomson, F. E. (2000) Nonvitamin, nonmineral dietary supplements: issues and findings from the third National Health and Nutrition Examination Survey. J. Am. Diet. Assoc. 100:447-454.[Medline]
15. Commission on Dietary Supplement Labels (1997) Report of the Commission on Dietary Supplement Labels 1997 Office of Disease Prevention and Health Promotion Washington D.C.
16. Neuhouser, M. L., Patterson, R. E. & Levy, L. (1999) Motivations for using vitamin and mineral supplements. J. Am. Diet. Assoc. 99:851-853.[Medline]
17. ConsumerLab. com. () Available at http://www.consumerlab.com/. Accessed May 2002.
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