Although US surveys have reported on current use of dietary supplements, data from the present study add unique information. To our knowledge, levels of supplement use among Japanese Americans and Native Hawaiians have not been specifically reported nor compared with levels of use among similar adults of African-American, Hispanic, or White ancestry. In addition, by excluding adults who reported certain major chronic diseases and/or risk factors for chronic disease, we minimized the influence of preexisting disease on the reported use of supplements. Finally, we analyzed both the frequency of supplement intake and the time period over which the supplement had been used, providing insight into changes in patterns of use.
Few other studies have reported supplement use by ethnicity. Neuhouser et al. (19
) defined regular supplementation as three or more times per week and reported levels of 53–70 percent among Black, Hispanic, White, and Asian males participating in the Prostate Cancer Prevention Trials. Frank et al. (10
), asking about current use of supplements five or more times weekly during the past month, reported levels of use of 58–65 percent among Hispanic, African-American, Asian, and White US female physicians. We found similar, yet slightly higher levels (62–69 percent) among our adults of these same ethnicities, who were representative of a broader range of socioeconomic levels. Nationally representative surveys report slightly lower use in the past month among US adults (35–55 percent) and use 7–10 percent lower among African-American and Hispanic adults compared with Whites (7
Our data are consistent with other reports indicating that multivitamins are the most frequently reported supplement type among all ethnic-gender groups (6
). The predominance of multivitamin use among these reportedly healthy participants is particularly interesting. Rather than augmenting a specific nutrient, most supplement users choose a product providing multiple nutrients for which dietary recommendations exist. This selection suggests that these adults are not worried about deficiencies in specific nutrients but may be more concerned about nutrient adequacy in general or possibly think that a multivitamin-type supplement provides assurance against nutrient deficiencies.
Use of any type of dietary supplement was approximately 14 percent greater, and use of multivitamins was approximately 8 percent greater, among women compared with men, regardless of ethnicity. The National Health Interview Survey and NHANES III found that approximately 6–8 percent more women than men use supplements (7
). In our data, the proportion of supplement users among men and women varied the most for calcium. Three times as many women as men reported use of calcium supplements regardless of ethnicity, suggesting that women may be more concerned about osteoporosis. Selenium and vitamin A were the only supplements for which intake among men and women did not differ substantially, although only 3 percent and 12 percent, respectively, reported use of either of these specific supplements.
Although patterns of supplement use varied little across ethnicities, there were two interesting exceptions. Age-standardized use of vitamin A and iron supplements among Latinos and African Americans was approximately twice that of the other ethnic groups, regardless of gender. This result suggests the possibility that supplemental intakes of these nutrients are being promoted among these ethnic groups or in Los Angeles; this finding should be investigated further. Additionally, substantially more Japanese-American and White participants in the current study reported long-term use of supplements, suggesting that use of various supplement products is relatively recent among the African-American, Native Hawaiian, and especially Latino participants.
In general, older persons were more likely to use supplements. However, similar to the findings of Frank et al. (10
) among African-American and Hispanic female physicians, dietary supplementation did not increase with age among our African-American and Native Hawaiian adults. The absence of a monotonic linear increase in supplement use with age for many groups may initially seem surprising. Instead, a threshold effect was observed, where use remained relatively constant after age 55 years. Supportive of this relation, a cross-sectional examination of our data revealed that reported supplement use increased with age among those in the 45–55-year age range. Supplement use may already be an established behavior after age 55 years.
Contrary to our expectations, factors associated in multivariate models with dietary supplement use tended to be similar across gender-specific ethnic groups. The lifestyle and demographic relations found suggest that a “health conscious” attitude predominates among dietary supplement users. Educational level was associated with a substantially increased likelihood of supplement use among all gender-specific ethnic groups except Japanese-American women. More years of education may imply a greater awareness of the role of nutrition in good health.
Similar to the findings of Houston et al. (8
), who assessed community-dwelling adults aged 60 years or older, and findings among men in the Prostate Cancer Prevention Trials, as reported by Neuhouser et al. (19
), obesity was inversely associated with supplement use, reinforcing the notion that supplement users focus attention on healthy behaviors. In the current analysis, this finding was consistent across ethnic populations, despite widely varying proportions of obese adults. Likewise, the reduced rate of supplementation among current smokers was consistent with the “healthy lifestyle choices” linkage to supplement use, as is the finding that former smokers were similar to never smokers in their dietary supplement use. Engaging in regular physical activity, again a healthy lifestyle choice, was significantly associated with an increased likelihood of supplement use, although usual hours spent watching television (as an estimate of sedentary behavior) was not related to use of dietary supplements. Healthy dietary choices, as measured by higher fiber and fruit intakes and by a lower fat intake, were also associated with supplement use among most of the gender-specific ethnic groups. Participants reporting the highest daily levels of dietary fiber intake were 40–82 percent more likely to report use of dietary supplements compared with those adults who had the lowest levels of daily fiber intake.
There are several caveats to the current analysis. By excluding those persons who had potential risk factors for and a history of cardiovascular disease and cancer, older participants were more likely to be excluded, and this exclusion was disproportionate across ethnic groups. The proportion of participants excluded because of cardiovascular disease risk factors ranged from 35 percent among Whites to almost 63 percent among African Americans. Ten percent of the White participants were excluded because of a previous cancer compared with only 5.5 percent of the Latinos. Thus, by intent, these findings apply only to persons reporting no history of these major chronic diseases.
Additionally, only eight specific supplement types were included in our assessment. By narrowing the focus of supplement types, we may have misclassified some participants as nonusers of supplements because they regularly used a type of dietary supplement excluded in our questionnaire. However, Murphy et al. (15
) compared supplement intake on the dietary history questionnaire and supplement intake reported on three 24-hour recalls for a representative sampling of the cohort and found that few participants used vitamin or mineral supplements that were excluded from the dietary history questionnaire.
Although the association of chronic supplement use with subsequent cardiovascular disease or cancer outcomes has been pursued in recent studies (23
), the populations were predominantly White, and associations for non-White adults have received little attention. Our analysis takes one step in that direction by reporting dietary supplement use among healthy African-American, Native Hawaiian, Latino, and Japanese-American adults and thus provides a basis for future analyses in relation to chronic disease outcomes.
Our models of demographic and lifestyle factors did not explain all of the variation between users and nonusers of dietary supplements. However, users could be distinguished from nonusers regarding factors thought to be indicative of a healthy lifestyle, regardless of gender or ethnicity. Such findings may be particularly important to consider in analyses of observational or prevention trials, and they highlight the difficulty in separating the effects of diet and supplement use on disease etiology. The high prevalence of dietary supplement use across the different ethnic populations reinforces the need to include supplemental sources when evaluating the relation between nutrient intakes and disease outcomes.