Dietary Supplements in Cancer Prevention and Therapy

Dietary supplements are regulated in the United States by the Food and Drug Administration (FDA) under authority of the Federal Food, Drug, and Cosmetic Act (FFDCA). An amendment to the FFDCA, the Dietary Supplement Health and Education Act of 1994 (DSHEA), defines a dietary supplement as a product that is intended to supplement the diet and contains at least one or more of certain dietary ingredients, such as a vitamin, mineral, herb or other botanical, or an amino acid. These products may not be represented as conventional foods and are marketed in forms that include capsules, tablets, gelcaps, softgels, and powders. Although manufacturers are required to have evidence to support their claims of a dietary supplement’s safety and efficacy, FDA approval is not required before a product is marketed. The passage of DSHEA played a role in increasing the use of supplements in the United States by ensuring consumer access to a wide range of such products (U.S. Congress, 1994). The legislation also created the Office of Dietary Supplements within the National Institutes of Health (NIH) with the mission “to strengthen knowledge and understanding of dietary supplements by evaluating scientific information, stimulating and supporting research, disseminating research results, and educating the public to foster an enhanced quality of life and health for the U.S. population” (Office of Dietary Supplements, 2004). Dietary supplements are commonly purchased and consumed in the United States even though they may not have proven benefits for the general population and, for some, may have harmful effects. However, the possibility that supplements help to prevent cancer development, progression, or reoccurrence attracts many people. A rigorous approach must be taken to determine the circumstances under which dietary supplements may have beneficial health effects on cancer or on any other disease or medical disorder. Special attention must be given to the circumstances that could influence the effects of dietary supplements, including the timing of supplement use, dose and dose–response, the role of specific supplement components, and the impact of interactive factors. This chapter addresses these issues with selected examples. Although it is beyond the scope of this chapter to address these issues for all supplements, the points made here are relevant to almost all categories of dietary supplements.