This study describes the relationship between several varieties of DS use and clinical and socio-demographic factors in a nationally representative sample of American adolescents. Overall, 27% of adolescents reported using a DS in the last month. DS use was higher among non-Hispanic whites, those who reported better health status, and those who used prescription medications. However, we did not find the expected association between DS use and gender, nor after controlling for other factors, between DS use and any specific health condition other than headache. The findings that the most commonly used DS by teens were multivitamins (16%) and vitamin C (6%) is reassuring in terms of potential health risks. The higher use of non-vitamin/mineral supplements among obese teens raises questions about the types and safety of the specific DS used in this growing population.
The prevalence of DS use in our sample was consistent with that found in other large studies that used different sampling techniques [4, 19, 26]. The use of some non-vitamin/mineral supplements (e.g. sport and herbal performance enhancers) in this sample was lower than in studies of teen athletes [27–32]. It was also lower than rates reported in clinically based surveys [3, 11, 12, 14, 33]. Differences in rates might be due to different usage in different groups, differences in the time period of use, and by different survey methods such as self report using the Internet vs. parent or adolescent response in a face to face interview .
In the adjusted model, certain demographic factors were associated with supplement use, while others were not. We confirmed findings of another large survey in which older adolescents were more likely than younger teens to use non-vitamin/mineral DS such as herbals, sports and weight loss products . Similarly, we confirmed earlier reports that non-Hispanic blacks and Mexican American adolescents use fewer vitamin/mineral DS than non-Hispanic white youth [4, 19]. On the other hand, unlike earlier studies, after adjusting for other factors, female gender was not significantly associated with DS use [4, 19]. Further studies are needed to understand how race, culture, income and health care disparities affect DS use and the impact of this use on health status.
As expected, certain clinical factors were also associated with DS use. For example, those reporting very good/excellent health status reported higher rates of DS use, confirming an earlier study . The direction of this association (Does use of DS cause good health or are healthy teens more likely to use DS?) is a worthy question for future research.
As expected, we found a higher rate of DS use among teens who reported using prescription medications than those who did not, even after adjusting for potential covariates [23, 24]. The etiology and clinical implications of the relationship between DS and prescription medication use requires additional exploration. Given reports about clinically serious interactions between prescription drugs and herbals/supplements, physicians and pharmacists need to be mindful of the higher use of DS among prescription users, ask prescription medication users about their use of DS, and monitor them for adverse effects or interactions.
The analysis of DS use by specific health conditions suggested mixed relationships. For example, obese youth were more likely to use non-vitamin/mineral DS than their peers. The higher use among obese teens is likely due to the inclusion of weight loss products in the non-vitamin/mineral DS variable; this finding deserves more specific scrutiny in future research for two reasons: a) rates of obesity are rising; b) weight loss products such as those containing ephedra can present risks of serious toxicity or drug-DS interaction. Also, adolescents with headaches were more likely to use DS, confirming earlier reports [35, 36]. Future analyses are needed to look specifically at different types of DS with different disorders and the impact of DS use on disease-specific outcomes including use of professional health care, health status, quality of life, and ability to work or attend school.
Despite its large size, national scope, and extensive, detailed ascertainment of DS use, this analysis has several limitations. First, proxy information was used for respondents less than 16 years old. Proxies (e.g. parents) could have overestimated multivitamin use and under estimated use of products teens may have purchased on their own such as weight loss and performance-enhancing supplements. Second, questions about dietary supplements may have missed products considered home remedies, folk remedies, or parts of the diet, such as green tea or foods containing supplements. Furthermore, the limited data on specific health conditions reduced our ability to assess the complex relationships between diseases and DS use. Finally, since NHANES did not ask about reasons for supplement use or the impact of this use on health status, we do not know why teens used certain supplements or how it affected their health .