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Supplement: Dietary Supplement Use in Women: Current Status and Future Directions

Dietary Supplement Use by American Women: Challenges in Assessing Patterns of Use, Motives and Costs

Cancer Prevention Research Program, Fred Hutchinson Cancer Research Center, Seattle, WA 98109-1024

²To whom correspondence should be addressed. E-mail: mneuhous{at}fhcrc.org.

	ABSTRACT

TOP ABSTRACT Methodological issues related to... Definition of dietary... Exposure assessment: frequency... Patterns of supplement use Supplements used to maintain... Supplements used to prevent... Supplements used to treat... Motivations for use of... Costs of dietary supplements Conclusions and future research... LITERATURE CITED

 
The 1994 passage of Public Law 103–417, the Dietary Supplement and Health Education Act, resulted in an exponential increase in the number and variety of dietary supplements available for over-the-counter purchase. Surveys conducted on random samples of U.S. residents have shown that approximately half of all American women use dietary supplements regularly, but very little is known about the risks and benefits of long-term and widespread supplement use. To accurately evaluate the health effects of supplement use, it is important to characterize usage patterns, motivations and costs of supplement use. However, this is a considerable challenge because accurate supplement data are difficult to collect, product databases with consistent and reliable information are lacking and survey instruments or interview protocols currently in use may not capture information about product selection for specific health conditions, motivations for use, or out-of-pocket expenditures. Future research would benefit from collaborative efforts among governmental scientists, academic scientists and industry to improve dietary supplement data collection methods and develop appropriate tools for analysis.

KEY WORDS: • dietary supplements • vitamins • minerals • nutrition surveys • epidemiologic methods

Dietary supplement use by American women has increased considerably in the past 10 y. Population-based surveys conducted among U.S. adults show that in the early 1990s about 25% of women reported regular supplement use, which increased to over 50% by the end of the decade (1–5). At least two factors account for this large increase over a short period. First, research findings published throughout the past 10–20 y have established that some supplements are very effective for disease prevention and their use has become a part of routine clinical practice [e.g., folic acid during the periconceptional period to reduce the risk of neural tube defects (6) and iron to prevent or treat anemia during pregnancy (7,8)]. Second, Public Law 103–417, the Dietary Supplement and Health Education Act (DSHEA) passed in 1994 (9) resulted in an exponential increase in the number and variety of supplements available for over-the-counter purchase. Specifically, DSHEA expanded the definition of dietary supplements to include ingredients not known to be required for human nutrition (i.e., herbs, glandular extracts), discontinued premarket safety evaluations for ingredients used in supplements, placed the burden of proof of product safety on the U.S. Food and Drug Administration (FDA) instead of the manufacturers and permitted limited nutrition support statements without prior approval from the FDA (9).

Very little is known about the risks and benefits of long-term and widespread supplement use. Investigating the consequences of this health behavior in American women has been identified as an important area of research (10). To this end an important task is to examine the current patterns of dietary supplement use in American women. The objective of this report is to describe the types of supplements used by adult American women, demographic characteristics associated with supplement utilization, motivations for use and economic effects. The information presented in this and other reports in this issue will be used to develop a focused research agenda for dietary supplement use in adult American women.

	Methodological issues related to collection of supplement use data

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Appropriate characterization of the patterns of dietary supplement use by American women requires careful collecting and reporting of data. These data are expensive and laborious to collect and the lack of a large product database with consistent and reliable ingredient information makes data coding and analysis complex. These methodological constraints limit the validity of results about patterns of dietary supplement use in American women.

	Definition of dietary supplements

TOP ABSTRACT Methodological issues related to... Definition of dietary... Exposure assessment: frequency... Patterns of supplement use Supplements used to maintain... Supplements used to prevent... Supplements used to treat... Motivations for use of... Costs of dietary supplements Conclusions and future research... LITERATURE CITED

 
Products defined as supplements by DSHEA include vitamins, minerals, herbs and amino acids, which are sold as capsules, gelcaps, tablets, powders or liquids and are intended to supplement the diet through increased dietary intake (9). These categories are not mutually exclusive, for example, many multivitamin and mineral preparations (e.g., Centrum® Performance^TM) contain herbs such as ginseng and Gingko biloba. In addition, numerous products do not strictly adhere to the DSHEA definition but are nonetheless marketed and used as dietary supplements. Estimating intake of these other substances presents a challenge for researchers because no uniform classification system for these products exists (11). Thus, it is difficult to design questionnaires or to conduct interviews that adequately capture these data. For example, the third National Health and Nutrition Examination Survey (NHANES III) used five categories to describe supplements that were neither vitamins nor minerals (herbals, other biological and nutrient supplements, body building supplements, weight loss and laxative-type supplements and miscellaneous supplements) (12). This type of classification system focuses on the product’s intended use rather than the product content. Alternatively, these same products could be classified by ingredients or the source of ingredients such as nonvitamin and nonmineral products (e.g., shark cartilage, animal glandular extracts), food derivatives (e.g., fish oil, flax seed oil, garlic, isoflavones) and endogenously produced substances (e.g., melatonin, creatine, cartinine, glutathione).

Many supplements are complex mixtures of as many as 20 or more micronutrients, botanical extracts and other biological materials, and no consensus exists among researchers on how to code these types of products. Because the number and type of nonvitamin and nonmineral supplements will likely increase over the next several years, expansion of the current DSHEA definition to include classification of these products could help researchers to uniformly collect and code these data.

	Exposure assessment: frequency and duration of supplement use

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Information on the frequency, duration and dosage of supplement use can enable researchers to estimate exposure over a long period, which is of interest for many diet-related chronic diseases. Quantification of intake can enable estimation of total micronutrients consumed when dosage information is used in conjunction with other dietary assessment measures. However, only recently has this level of detail been incorporated into research protocols. From the 1980s to the early 1990s, observational and intervention studies with nutrition-related objectives collected information only on multivitamins or multivitamins with minerals and a few commonly used single-nutrient supplements (e.g., vitamins A, C, E, iron, calcium) (13–15). Self-administered questionnaires or in-person interviews inquired about use of dietary supplements as a simple question with yes/no response options (13–15). These early studies provided information on the prevalence of supplement use but no data on patterns of use or potential dose-response effects, which limits the ability to draw any etiological inferences (16).

As a result of both increased supplement use in the 1990s and the recognition that supplement use may be an important exposure for disease risk, scientists have developed more detailed data collection methods that include quantitative questions on dosages of micronutrients, duration of use (e.g., weeks, months, years) and frequency of use (e.g., daily, weekly) (1,17,18). Despite these improvements in study design, data collection methods still vary widely across studies. For example, the American Cancer Society Cohort Study inquired about duration and frequency of use of multivitamins and single supplements of vitamins A, C and E (19) whereas the Continuing Survey of Food Intake in Individuals collected data on the frequency of multivitamins, multivitamins with minerals, and 13 single supplements (20). The Women’s Health Initiative uses a detailed inventory system to collect dose, frequency and duration data on supplements that are of interest to its scientific objectives (e.g., calcium) (18). Participants in a large cohort of supplement users in western Washington State complete a detailed seven-page booklet on frequency, dose and duration for multivitamins, multivitamins with minerals (including specialty types such as antioxidant or "stress-type mixtures"), single supplements, herbs, and food derivatives, such as garlic and fish oil (21). Other studies have gathered information on the brand name of supplements used by participants (22,23). Clearly, methods for collection of dietary supplement data are not standardized and only a few investigators have conducted validity studies of methods used to assess supplement intake (18,21). The authors of one of these validity studies concluded that many commonly used methods for obtaining dietary supplement data have substantial amounts of error, and these authors called for more careful design of supplement assessment instruments to reduce the possibility of measurement error and attenuation of relative risk estimates in studies with disease endpoints (17).

There are other methodological issues concerning collection of dietary supplement data. First, protocols that only record the brand name of the supplement may misclassify dosages of nutrients assigned to study participants; formulations of the same product by the same manufacturer change over time so that recording a brand name only will not ensure consistent product content. Second, content and dose information cannot be obtained for most botanicals because there are no product specification standards for herbs and other supplements (9,10). For example, for a product labeled echinacea, the manufacturer is not required to indicate whether the product was derived from the flower, leaf, stem or root, each of which has different bioactive or marker compounds (24). Third, use of many herbs (e.g., echinacea) and single supplements (e.g., vitamin C) fluctuates according to menstrual cycle symptoms, illnesses such as colds and flu or general stress levels. Questionnaires or interview protocols that only inquire about frequency of use in the past month or year, but not the past week, may not capture this sporadic use.

Although occasional use is not likely to be important for chronic disease risk assessment, there are critical time periods in a woman’s life when acute exposure to a nutrient or substance may have important beneficial or adverse consequences. For example, exposure to the herb feverfew in pregnancy has been associated with an increased risk of spontaneous abortion, and black cohosh and blue cohosh can stimulate uterine contractions, which could be detrimental in early or midpregnancy (25,26). Lack of exposure to folic acid during a narrow but critical period of embryonic development (26–28 d gestation) can result in a neural tube defect (27) whereas excessive vitamin A in early pregnancy is teratogenic (28).

Tens of thousands of products are sold in the United States, each with a different combination of micronutrients, botanicals and other ingredients. Construction and management of a useable database to incorporate such data into analysis is being used in one large dietary intervention study (23), but most studies have neither the resources nor the database expertise for such an endeavor. Efforts to construct a national database that could be available to all researchers in this area could greatly benefit the scientific community.

	Patterns of supplement use

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Despite the limitations in methodology noted above, many studies have provided useful information about the demographic and lifestyle characteristics of supplement users. These studies consistently show that women who use supplements tend to be Caucasian, be well educated, live on the West coast and have an income that is greater than the median U.S. income (1–3,29,30). Compared with women who do not use supplements, supplement users are also more likely to have a lower body mass index, be nonsmokers, exercise regularly, eat more fruits and vegetables and adhere to cancer screening recommendations (1–3,29,30). Recognition that these demographic and lifestyle characteristics are strongly associated with supplement use has been especially important in studies with disease endpoints when they are modeled as confounders in the analysis (31). An additional useful paradigm for characterization of supplement patterns is intended usage in one of three principal categories: health maintenance, disease prevention and disease treatment.

	Supplements used to maintain health

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Multivitamins (with or without minerals), the supplements most commonly used by American women (32), are most likely to be used to maintain general good health. Eldridge et al. (33) reported that in a sample of 502 college students, vitamins were used to ensure adequate nutrition and provide "pep and energy." Perkin et al. (34) recently surveyed 263 college students on their use of nonvitamin, nonmineral supplements and found that 61% used these products to improve energy, 35% used them to supplement an inadequate diet and 36% used them to burn fat. This same study, as well as results from NHANES III, showed that nonvitamin, nonmineral supplements are used to build muscle or improve athletic performance (12,34). Body building, performance enhancement, efforts to increase energy and the desire to optimize nutrient intake are all consistent with a desire to maintain overall general health.

	Supplements used to prevent disease or condition

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Several nutrients are associated with a decreased incidence of specific disorders throughout the adult female life cycle, especially when ingested as supplements. For example, there is overwhelming evidence that periconceptional use of folic acid-containing supplements substantially reduces the risk of a neural tube defect-affected pregnancy (6,27). Interestingly, despite national policies to promote the use of folic acid, a March of Dimes survey reported that among women aged 18–45 y only one-third used a daily supplement containing folic acid (35). Among minority and low income women, prevalence of folic acid use is even lower. Kloeblen (36) reported that although 65% of a sample of 251 low income women knew that folic acid prevented birth defects, only 20% used periconceptional supplements. Similarly, in a study of 471 African American and Hispanic women, 17% had heard of neural tube defects and only 11% knew that folic acid could protect against these malformations (37). Clearly, research is needed to investigate why there is a low prevalence of use of a supplement for which there is strong evidence of benefit.

Several intervention studies have tested the effectiveness of specific supplements to prevent certain diseases or conditions. For example, at least 35 randomized-controlled trials have shown that supplemental calcium or calcium-vitamin D combinations increase bone mass and decrease fracture risk in adult females (38). Additionally, numerous observational studies have shown associations of dietary supplement use with reduced risk of cardiovascular disease, signs of aging, cognitive decline, affective disorders and some cancers (39,40). However, very little is known about whether the decision to use specific supplements is based on these published observations.

	Supplements used to treat disease or condition

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Consumers may be particularly attracted to supplements that promise cures or effective treatments for diseases or conditions. Specifically, many products promise an enhanced immune system, weight loss, decreased stress and amelioration of symptoms associated with the female menstrual cycle.

Weight management is a health concern of primary importance to American women, and thus it is not surprising that dietary supplements are used together with other measures such as exercise and dietary modifications. Levy et al. (41) reported results from a population-based telephone survey that showed that 71% of the women interviewed reported current attempts to lose weight. Of these women, 33% used vitamin and mineral supplements as part of their weight loss program. Results from NHANES III showed that specific supplements (kelp, lecithin and vitamin B-12) were used as weight loss aids (12). The 1998 Behavioral Risk Factor Surveillance System survey found that 48% of 8546 female respondents were overweight or obese (42). Ephedra products, which are classified as dietary supplements by DSHEA, were reportedly used by about 2% of these women as their primary weight loss tool.

Anecdotal evidence suggests that women use supplements to treat two common premenopausal conditions: benign breast disease and premenstrual syndrome. Although data to support efficacy are inconclusive, vitamin E, evening primrose oil and vitamin B-6 are often used to treat the symptoms of benign breast disease (43). Calcium, magnesium, vitamin B-6, vitamin E, St. John’s wort, kava and evening primrose oil are reportedly used to treat a variety of symptoms associated with premenstrual syndrome (44). However, no population-based prevalence data show the proportion of women who routinely use these supplements to self-treat these specific conditions.

Several studies have investigated associations of supplement use and breast cancer treatment. Newman et al. (23) reported that of 435 women diagnosed with breast cancer, 81% used multiple vitamin, mineral and herbal products. In another study of women with breast cancer, Burstein et al. (45) reported that 9% of the patients began the use of megavitamins or herbals after their breast cancer diagnosis, and the Women’s Physician’s Health Study found that women diagnosed with breast cancer were 1.5 times more likely to use supplements than were women without breast cancer (46). Patterson et al. (47) recently reported that there were statistically significant positive associations between receiving multiple medical treatments for breast or colon cancer and new use of dietary supplements after diagnosis. The results from these studies suggest that women who have a potentially life-threatening illness, such as cancer, are heavy users of dietary supplements, but the specific beliefs about these products and associations with long-term outcome have not been well characterized.

	Motivations for use of dietary supplements

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Motivations for use of dietary supplements are complex but are likely related to perceived susceptibility to illness; current health status, including whether a woman experiences symptom distress or impaired quality of life related to a specific illness or condition; locus of control; beliefs about the efficacy of specific products; and economic factors. In a study of supplement users in Washington State, 41% of the participants used multivitamins to feel better whereas they used vitamin C, vitamin E and calcium for specific presumed preventive benefits, namely, prevention of colds and flu, heart disease and osteoporosis, respectively (48). In this same study many respondents reported supplement use for vague reasons such as doctor’s advice, need to boost the immune system and recommendation of the sales clerk at the health food store. These responses suggest that beliefs and attitudes about supplement use are multifaceted and may be difficult to characterize using standard epidemiologic questionnaires. Nutrition scientists and others conducting research on dietary supplements would benefit from collaboration with behavioral scientists to design valid, reliable instruments to measure supplement use behavior and health beliefs about supplements that may motivate their use (49).

	Costs of dietary supplements

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Industry reports show that Americans spend over $12 billion per year on dietary supplements (50). Only a few studies in the peer-reviewed literature have presented supplement expenditure data (4,47), but an assessment of these large, out-of-pocket costs is important for two reasons. First, personal health expenses, including supplements, comprise a portion of total health care expenditures. The influence of lifestyle behaviors on total health care costs has been traditionally restricted to habits such as smoking, alcohol use and exercise patterns (51,52). Nonetheless, given that the majority of Americans use supplements at least occasionally, the net effect on total health care costs deserves examination in greater detail. Second, and perhaps more importantly, supplements are increasingly prescribed or recommended as part of primary treatment plans or as components of prevention strategies, but they are infrequently covered by either fee-for-service or managed care health plan benefits. For example, the U.S. Public Health Service and the Institute of Medicine recommend periconceptional use of folic acid supplements by all women of childbearing potential (6), but the cost of these supplements must be borne entirely by the patient. Research is needed to determine whether effective implementation of this policy is hindered by inability to purchase the recommended supplements. Other supplements often prescribed to women include multivitamins and iron during pregnancy, calcium throughout the adult life cycle to prevent osteoporosis, and more recently, St. John’s wort for mild depression and glucosamine chondroitin for joint health. When these and other supplements are prescribed by physicians as a component of the patient treatment plan, it is reasonable to suggest that in terms of reimbursement rates, supplements should be given consideration that is comparable with the prescription drugs they are replacing or complementing.

	Conclusions and future research recommendations

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This report has highlighted some of the challenges associated with characterizing patterns of dietary supplement use, motivations for use and costs. Many questions remain about the long-term risks and benefits of supplement use and how to optimally design studies to answer these scientific questions. Future research needs to include construction of a useable supplement database; improvement of data collection instruments; research on patterns of supplement use among women who do not volunteer for research studies, such as those who experience food insecurity and nonnative English speakers; collaboration with behavioral scientists to investigate motives for supplement use, especially research on barriers to use of supplements for which there is a known health benefit; and investigation of out-of-pocket expenditures or reimbursement rates for dietary supplement use.

A focused research agenda on dietary supplements, which includes collaboration among the National Institutes of Health, academic scientists and industry partners, will provide data to help answer scientific questions with important public health implications.

	FOOTNOTES

 
¹ From the National Institutes of Health (NIH) conference "Dietary Supplement Use in Women: Current Status and Future Directions" held on January 28–29, 2002, in Bethesda, MD. The conference was sponsored by the National Institute of Child Health and Human Development and the Office of Dietary Supplements, NIH, U.S. Department of Health and Human Services (DHHS) and was cosponsored by the Centers for Disease Control and Prevention, Food and Drug Administration Office of Women’s Health, NIH Office of Research on Women’s Health, National Institute of Diabetes and Digestive and Kidney Diseases Division of Nutrition Research Coordination, DHHS; National Center for Complementary Medicine, U.S. Department of Agriculture Agricultural Research Service; International Life Sciences Institute North America; March of Dimes; and Whitehall Robbins Healthcare. Conference proceedings were published in a supplement to The Journal of Nutrition. Guest editors for this workshop were Mary Frances Picciano, Office of Dietary Supplements, NIH, DHHS; Daniel J. Raiten, Office of Prevention Research and International Programs, National Institute of Child Health and Human Development, NIH, DHHS; and Paul M. Coates, Office of Dietary Supplements, NIH, DHHS.

³ Abbreviations used: BDSHEA, Dietary Supplement and Health Education Act; FDA, U.S. Food and Drug Administration; NHANES III, third National Health and Nutrition Examination Survey.

	LITERATURE CITED

TOP ABSTRACT Methodological issues related to... Definition of dietary... Exposure assessment: frequency... Patterns of supplement use Supplements used to maintain... Supplements used to prevent... Supplements used to treat... Motivations for use of... Costs of dietary supplements Conclusions and future research... LITERATURE CITED

 

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