The benefits of herbal and other natural products (dietary supplements) are increasingly cited in the media. Dramatic increases in use reported during the last decade have led to growing concerns about efficacy and safety.
To determine which dietary supplements American adults use, whether the prevalence has continued to increase in recent years, and whether popularity of individual supplements has changed, demographic information and details of use of all medicines and dietary supplements in the preceding week were obtained by telephone interview from February 1998 through December 2002 from households in 48 contiguous states and the District of Columbia. Participants included randomly selected residents of households with telephones; compared with 2000 US Census data, participants were representative of the US population. The main outcome measure was the weekly prevalence of dietary supplement use, alone or in a multicomponent product.
There were 8470 subjects 18 years or older. The annual prevalence of dietary supplement use increased from 14.2% in 1998-1999 to 18.8% in 2002. Although use did not change among younger subjects, it doubled for men and women 65 years or older. Use of Ginkgo biloba and Panax ginseng declined during the study, while lutein use increased dramatically, because of its addition to multivitamin products. The overall 2002 prevalence excluding lutein use was 13.9%.
The popularity of specific supplements has varied over time and differs according to age and sex. The sharp increase in supplement use in the 1990s appears to have slowed. However, the addition of supplements, such as lutein and lycopene, to mainstream multivitamins has become an important source of exposure.
The use of alternative medicines in the United States, particularly herbal products, increased dramatically during the last decade.1 In 2001 alone, Americans spent $4.2 billion on herbs and other botanical remedies.2 Although this issue now receives considerable attention in the medical and lay press, few details about the frequency and nature of use of herbal and other natural products (herein referred to as dietary supplements) have been published. Because such information is important to the clinical and research communities, we examined recent trends in the use of dietary supplements, using data from the Slone Survey, a telephone survey of a random sample of the US population that has been ongoing since 1998. Individual vitamins and minerals are not considered in this report.
The methods have been described in detail.3 A brief summary follows.
Residents of households with telephones in the 48 contiguous states and the District of Columbia are eligible for inclusion in the survey. Subjects are identified by random digit dialing; multiple attempts are made during 1 to 2 months before a telephone number is considered unreachable. At each contacted number, one individual in the household is selected for interview by a computer-generated random number procedure. The interviews are administered by specially trained interviewers employed by the Slone Epidemiology Center.
After demographic information is obtained, the subject is asked to gather and identify all prescription and over-the-counter medications and dietary supplements taken during the preceding 7 days. The interview includes explicit inquiries about herbal medicines. After the product and brand names of these medications have been recorded, a list of reasons for use (eg, pain, headache, backache, depression, tension, or emotional disorders) is read to elicit recall of other drugs, particularly over-the-counter medications and dietary supplements. For all reported medicines, information is obtained on reason for use, route of administration, number of days taken in the week before the interview, and total duration of use.
Medication names are coded for analysis using a dictionary developed and maintained by the Slone Epidemiology Center. The dictionary is a computerized linkage system composed of individual agents and multicomponent products, including dietary supplements, each assigned specific code numbers. All combination products are linked to their individual components. The components of dietary supplement products are identified by a pharmacist using multiple sources, including the Natural Medicines Comprehensive Database,4German Commission E Monographs,5Botanical Safety Handbook,6PDR for Herbal Medicines,7Herbs of Commerce,8 web sites, product labels and catalogs, and texts on homeopathic medications, Chinese herbal agents, and ayurvedic products.
The terminology used for dietary supplements is evolving and nonstandard. For the purposes of this analysis, we define a supplement as an herbal or other natural product; individual vitamins or minerals are not included. Herbal refers to plant or algae substances or their extracts, and other natural product refers to substances derived from other natural sources (eg, animal organs and marine exoskeletons) and include amino acids and enzymes.
There were 10 470 subjects interviewed from February 1998 through December 2002; the participation rate was 67.8%. Based on a comparison with US Census data from 2000,9 the study population was similar to the US population with regard to age (median age, 34 years in the Slone Survey vs 35 years nationally), race (white, 74.5% vs 75.1%; and African American, 10.1% vs 12.3%), Hispanic ethnicity (12.0% vs 12.5%), and geographic region (the proportions in each of the 4 major census regions [Mountain Pacific, South Central, North Central, and Northeast] were within 1%). Minor differences were observed for sex (female, 53.7% vs 50.9%) and annual household income, with the study population having fewer subjects with incomes less than $10 000 (4.9% vs 9.5%). The largest difference was observed for education level, with the survey including more subjects with advanced degrees (11.4% vs 8.9%) and fewer who had not graduated from high school (12.5% vs 19.6%).
The results that follow are based on the 8470 subjects who were at least 18 years of age. All percentages are adjusted for household size, a factor that affects the probability of an individual being included in the survey.
Age, sex, and prevalence of supplement use according to year of interview are shown in Table 1. The median age was stable over time; the proportion of female subjects varied from 54.0% to 58.3%. Because of the similarity in age and sex distributions, no adjustment was made for these factors in the comparisons of supplement use among study years. Overall, 15.9% of subjects had used 1 or more supplements during the previous week; the prevalence of use varied, with a low of 12.3% in 2000 and a high of 19.8% in 2001.
Various characteristics of subjects according to use of supplements are shown in Table 2. Users were older (median age, 49 vs 42 years) and more likely to be female (59.9% vs 55.5%) and white (80.7% vs 75.6%) than nonusers. Users also included a higher proportion of subjects from the Mountain Pacific states than nonusers (27.0% vs 21.2%). Annual household income and education level were higher among users.
Use of supplements among men and women is shown according to age and year of interview in the Figure. Among men aged 18 to 44 years, there was no consistent variation over time, while the prevalence of use in those aged 45 to 64 years increased by about half between 1998-2000 and 2001-2002. Supplement use increased each year among the oldest men, but it doubled between 2000 and 2001; by 2002, men 65 years or older had the highest prevalence, at 22.7%.
The youngest women had the lowest use throughout the study, and the highest prevalence for this group was 16.3%, in 2001. Use was greatest among women aged 45 to 64 years in each year but the last; there was a modest increase between 1998-1999 and 2002 (23.5% to 28.7%), with a decrease in 2000 (17.7%). Similar to what was seen in men, supplement use among the oldest women nearly doubled between 2000 and 2001, increasing from 14.6% to 26.1%; by 2002, older women were the heaviest users.
The prevalence of use for each of the most commonly reported supplements in 1998-1999 and in 2002 is shown according to age in Table 3 (men) and Table 4 (women). There were numerous changes in use over time and within age-sex groups. Among male subjects aged 18 to 44 years, Panax ginseng, the supplement with the highest prevalence in 1998-1999 (4.1%), was used by only 2.1% in 2002 (Table 3). The next most commonly reported supplements for this age group in 1998-1999, creatine and saw palmetto (Serenoa repens), were not among the top supplements in 2002. In middle-aged men, use of garlic (Allium sativum) did not differ over time, but use of Ginkgo biloba, Panax ginseng, and St Johns wort was lower in 2002 than in 1998-1999, while use of saw palmetto, glucosamine, and chondroitin increased. In the oldest men, use of chondroitin more than tripled, prevalence of saw palmetto use declined from 4.4% to 2.6%, and garlic, used by 3.6% in 1998-1999, was not among the top supplements in 2002. While in 1998-1999 the most common product varied according to age, lutein was the most commonly used supplement among men of all ages in 2002; use ranged from 3.5% in the youngest men to 13.4% in the oldest. The highest age-specific prevalence of use of this substance in 1998-1999 was 1.2%, among men aged 45 to 64 years.
For women aged 18 to 44 years, none of the top 6 supplements in 1998-1999 was in the top 5 in 2002 (Table 4). Although the ranking of glucosamine fell to second in 2002 among middle-aged women, the prevalence increased to 8.6%; chondroitin gained in popularity, while use of Ginkgo biloba, Panax ginseng, and garlic declined somewhat. Among women aged 65 years or older, use of glucosamine almost doubled from 1998-1999 to 2002, with use rising from 5.2% to 9.8%. Use of Ginkgo biloba and Panax ginseng declined moderately, while garlic, used by 2.6% early in the survey, was not among the top 10 supplements in 2002. As was the case for men, lutein was the most commonly used supplement among women in all age groups in 2002, whereas it was not among the top supplements in any age group in 1998-1999.
Given the predominance of lutein in the most recent data, we examined use of this substance in more detail. The weekly prevalence of lutein use in all subjects combined was 0.3%, 0.5%, 6.6%, and 8.4%, respectively, in 1998-1999, 2000, 2001, and 2002. Lutein exposure was almost exclusively in the form of a component of a multivitamin product. Although lutein is a carotenoid, it is not a provitamin A; most lutein used in this country is derived from marigolds10 and is thus classified herein as an herbal supplement. When this compound is excluded, the prevalence of dietary supplement use was 14.2%, 12.2%, 16.1%, and 13.4% during the 4 consecutive periods of data collection, with an overall prevalence of 13.9%.
The reason for taking any product containing herbal and other natural supplements was examined for subjects interviewed in 2002 (Table 5); reasons are listed separately for men and women, in descending order of frequency. The 2 most common reasons reported by both sexes were “vitamin” and “supplement diet,” at 21% and 12%, respectively. Other common reasons among men were “energy” (7.0%) and “prevention, not otherwise specified,” “physician recommended,” and “health,” each at 5.9% to 6.4%. Women reported “health” (7.2%) and “physician recommended” (4.7%) at similar proportions as among males. “Energy,” “menopausal symptoms,” and “immune booster” each accounted for approximately 4% of the use of herbal and other natural supplements among women. Only 1 of the 148 subjects who used lutein-containing products in 2002 reported “eyes” as the reason for use; most use was for nonspecific reasons such as “vitamin” and “health” (data not shown).
Recognition of a sharp upward trend in the use of dietary supplements during the 1990s1 has resulted in a more widespread awareness of and interest in these products.11-13 Understanding patterns of supplement use is helpful in encouraging communication about supplement use between patients and their health care providers, and it is important to public health efforts, such as discouraging use of ephedra-containing supplements (linked to the occurrence of seizures, myocardial infarction, and stroke).14,15
The present data demonstrate that, in any week in 2002, 18.8% of American adults used a dietary supplement containing an herbal or other natural product. Although this prevalence is higher than the 14.2% observed in 1998-1999, the increase is explained by a dramatic rise in exposure to lutein in 2001 and 2002. In contrast, when lutein (almost exclusively ingested as a component in a multivitamin product) is excluded, the prevalence is unchanged during the study. Therefore, it appears that use of dietary supplements in the form of individual herbs or herbal mixtures has reached a plateau.
Use of supplements in general varies according to age and sex, as does the use of specific products. Based on answers to an open-ended question, there was a large variety of reasons reported for use of herbal and other natural supplement–containing products. Reflecting the increasing trend for herbal and natural products to be taken in the form of a multivitamin, it is not surprising that one third of men and women reported use for the reasons “vitamin” and “supplement diet”; use for more specific reasons, such as “prevent colds” and “insomnia,” was reported at much lower frequencies. The survey does not obtain information on medical history; therefore, we cannot comment on the relationship between underlying disease and the use of supplements. As has been observed previously, supplement users are more likely than nonusers to be women, white, well educated, and of higher socioeconomic status.16,17 In addition, we found that, although overall use remained stable over time, the popularity of individual supplements has changed considerably, with notable examples including the increasing use of glucosamine and chondroitin and the declining use of St Johns wort.
The survey population in the present report is similar to the US population, based on comparisons with 2000 US Census data. Most differences identified were small, with the largest being an underrepresentation of individuals with lower education levels; this is a known aspect of random digit dialing surveys.18 The possibility of bias because of differences in use of dietary supplements between participants and nonparticipants cannot be excluded, but our participation rate of 67.8% is high for such studies.19 While completeness of reporting may have differed according to supplement, the interview process was carefully designed to maximize recall and reporting accuracy. All interviewers were rigorously trained to conduct the interviews in a consistent manner, the exposure interval of interest was brief and recent, and subjects were asked to confirm the names of medications from containers. Therefore, data from the Slone Survey likely provide an accurate and comprehensive picture of dietary supplement use in the US population.
Previous data on supplement use in the United States include a survey in 1990 by Eisenberg et al20 that documented a 12-month prevalence of 2.5% for use of any herbal preparation. When a similar survey was conducted in 1997, the prevalence had increased to 12%.1 Although these figures are not comparable to those in the present survey, because the exposure period was 1 year rather than 1 week, they are relevant insofar as they demonstrate a major increase in use of these substances during a short period.
Data from the third National Health and Nutrition Examination Survey,21,22 based on a nationally representative sample of the US population surveyed between 1988 and 1994, are more directly comparable to those in the present survey. Information was obtained on use of dietary supplements in the prior month, and the 1-month prevalence of use of any supplement other than vitamins or minerals was 3.6%,22 substantially lower than the present observation of the weekly prevalence a decade later.
Based on data from the 1999 National Health Interview Survey, Ni et al23 reported on use of complementary and alternative medicine. Information was obtained on 11 therapies, including herbal medicine, acupuncture, and biofeedback. The 12-month prevalence for herbal medicine use was 9.6%, substantially lower than the 1-week prevalence estimate of 14.2% for the same period in the present study. The authors suggest that in-person interviews in the National Health Interview Survey allowed inclusion of subjects not covered by telephone or mail surveys, that is, those who have lower incomes and are less educated, who tend to use fewer complementary and alternative medicine therapies.
Our observations regarding lutein use were unexpected. This carotenoid antioxidant was first added to many popular multivitamin products in late 1999 and 2000, based on evidence that lutein intake was inversely associated with risk of macular degeneration,24,25 an important cause of blindness in adults. It is of interest in this context that the reported reasons for use of lutein are nonspecific, reflecting its general use as a component of multivitamins. More recently, another antioxidant, lycopene, was added to major multivitamin products as a cancer preventative beginning in early 2003. The addition of these supplements to multivitamin products has signaled 2 subtle, but important, changes in recent years. First, the acceptance of herbal substances and other dietary supplements as part of the mainstream health milieu has apparently increased. Second, the marketing strategy for multivitamin products appears to have broadened from supplying recommended daily allowances of vitamins and minerals that may be lacking in the diet to preventing chronic disease, such as macular degeneration and cancer. This viewpoint has been bolstered by the recent recommendation by Fletcher and Fairfield26 that all adults should take a multivitamin daily for chronic disease prevention.
Because all herbal products are complex mixtures that may include multiple active ingredients, it is not surprising that there is little evidence-based information regarding the biologic effects of these substances. Some, such as Panax ginseng and Gingko biloba, which are included in certain multivitamin products targeted for older users, are known to have anticoagulant effects.27 Although there are no specific safety concerns regarding exposure to lutein or lycopene thus far, their recent addition to multivitamins raises a larger public health issue. Subjects who are exposed to lutein or other dietary supplements in a multivitamin may be unaware of the presence of these substances in the product they are using. Approximately one quarter of adults in the United States use multivitamins,3 and this prevalence may increase following the recent recommendation that all adults take a multivitamin daily.26 Although the deliberate use of herbal products may have reached a plateau in the last few years, exposure to individual herbal ingredients may continue to rise as more of them are added to mainstream multivitamin products.
Correspondence: Judith P. Kelly, MS, Slone Epidemiology Center, Boston University School of Public Health, 1010 Commonwealth Ave, Boston, MA 02215 (firstname.lastname@example.org).
Accepted for Publication: September 30, 2004.
Funding/Support: The Slone Survey was supported by Slone Epidemiology Center funds.
Acknowledgment: We thank Anthony Roman for his helpful advice on methods and for providing the sample of telephone numbers. We also thank Kathy Lehmann, Marie Berarducci, and Marilyn Wasti for supervision of the survey staff; John Farrell, John Roberge, Gene Sun, and Michael Bairos for computer database development; and the interviewers: Marie Campesano, Jennifer Connell, Deborah Connelly, Melissa Cooper, Clare Coughlin, Joan Curran, Dorothy Domino, Sandra Finder, Mary Fitzgerald, Kathleen Foster, Fred Furnari, Maureen Gatulis, Michael Hoagland, Ann Hoey, Deborah Kasindorf, Linda Kasparian, Mary Kreiger, Megan O’Brien, Jay Walsh, and Barbara Winter.
Financial Disclosure: None.
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