What are dietary supplements?

Quick Answer
A broad category of materials that are defined as substances consumed in addition to a person’s normal diet.
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Cancers treated or prevented: Dietary supplements are often taken, in an adjuvant mode, to help fight many types of cancer, although their effectiveness is rarely proven. Perhaps even more often, supplements are taken for cancer prevention or to boost the immune system.

Delivery routes: Oral in the form of tablets, caplets, capsules, powders, and liquids such as extracts and teas.

How these agents work: Worldwide in 2012, dietary supplements were estimated to be a $32 billion industry. Supplements range from familiar multivitamin tablets to unusual substances such as snake venom. Some dietary supplements (such as vitamins and minerals) have accepted roles in conventional medicine as well as complementary and alternative uses. Other dietary supplements, including most botanicals, are used almost exclusively in complementary and alternative medicine. Complementary medicine supplements traditional Western medical care, while alternative medicine seeks to replace traditional Western medical care.

Some dietary supplements, especially vitamins and minerals, are embraced by traditional Western medicine and play an important role in maintaining health, especially among individuals with cancer or other diseases that affect the body’s metabolism. Thirteen different vitamins are essential to human health. The body cannot make these compounds; they must be obtained either from food or from dietary supplements. The fat-soluble vitamins are vitamins A, D, E, and K. The water-soluble vitamins are vitamins B1 (thiamine), B2 (riboflavin), B3 (niacin), B5 (pantothenic acid), B6 (pyridoxine), B7 (biotin or vitamin H), B9 (folate or folic acid), B12 (cobalamin), and vitamin C. Vitamins are generally safe when taken in amounts less than the upper safe limit set by the US Institute of Medicine. Megadosing, or taking large quantities of vitamins, can cause serious health complications, especially with the fat-soluble vitamins, which build up in the body. Minerals are inorganic compounds found in the earth that are necessary in small amounts for human health. Like vitamins, many minerals are safe and effective unless taken in megadoses.

Botanicals (herbs) are dietary supplements derived from plants. Botanicals have been used for centuries in traditional Chinese medicine, Ayurvedic or traditional Indian medicine, pre-nineteenth-century Western medicine, and homeopathy. The National Center for Complementary and Alternative Medicine (NCCAM) conducts rigorous investigations and clinical trials of many botanicals. Common botanicals that are claimed to treat cancer or cancer symptoms include apricot pit, foxglove, ginseng, green tea, and reishi mushroom. These claims have not been proven to the satisfaction of Western medicine.

Amino acids are molecules that are the building blocks of proteins. Humans require twenty amino acids, twelve of which the body can produce for itself. The rest must be obtained through diet or supplementation. Enzymes are proteins made in the body that regulate metabolic reactions. Prescription enzymes and amino acids are used in Western medicine when they replace compounds that the body is unable to make because of genetic defects. These substances are also sold as dietary supplements, some of which claim to treat cancer. Most traditional physicians do not accept these claims.

Animal-based supplements include products such as fish oil, bee pollen, and bear bile. Many of these products are used in alternative medicine and claim to prevent or treat disease. Practitioners of Western medicine generally acknowledge the benefits of some dietary supplements, such as vitamins, minerals, and fish oils, but question extreme claims.

In relation to cancer, people generally take dietary supplements for four reasons: to prevent a particular type of cancer; to meet the needs for a particular substance that they cannot acquire from diet because of their cancer (vitamin supplements); to boost the immune system and help it fight their cancer (ginseng); and to reduce specific symptoms associated with their cancer (ginger for nausea). The American Cancer Society cautions individuals with cancer to choose dietary supplements with care and with the knowledge and advice of their physician. Much misinformation and many unproven anecdotal claims about dietary supplements and cancer exist on the Internet and in some fad medicine books.

Although millions of Americans use dietary supplements daily, the safety and effectiveness of these products varies depending on the type of supplement, the purity of the manufacturing process, the dosage, the health of the individual, and the way in which the supplement interacts with other supplements and drugs. In the United States, dietary supplements are regulated under the 1994 Dietary Supplement Health and Education Act (DSHEA). This act regulates supplements as foods rather than as pharmaceutical drugs. Under the act, dietary supplement manufacturers do not need to prove that their products are either safe or effective before they are marketed. This contrasts with both over-the-counter and prescription drugs, which cannot be sold until extensive testing (clinical trials) proves them to be both safe and effective in treating specific conditions.

DSHEA limits the health claims that can be made for dietary supplements. Supplements cannot legally claim to treat or cure a particular disease. They are, however, allowed to make general claims, such as “helps build strong bones” or “helps lower cholesterol.” Any structure or function claims made for dietary supplements must have on the label the exact words, “This statement has not been evaluated by the FDA. This product is not intended to diagnose, treat, cure, or prevent any disease.” The packaging does not have to contain any warnings about potential side effects.

Additional FDA regulations have been added since the original 1994 law. By the end of 2007, all supplement manufacturers were required to report consumer complaints, including complaints of adverse reactions, ineffectiveness, and contaminated products, to the FDA. Before 2007, there was no requirement to inform the FDA of any problems reported by consumers. In addition, in June, 2007, new FDA regulations established stronger good manufacturing practices for dietary supplements that required manufacturers to test for the identity, purity, strength, and composition of their products. These regulations were intended to help consumers determine exactly what is in the supplement and to certify that it is free from contamination by bacteria, fungi, glass, pesticides, heavy metals, and nonapproved additives.

The new manufacturing regulations resulted from findings by independent laboratories and the FDA of many contaminated supplements, as well as those that contained material other that what was listed on the label or that contained less or none of the labeled ingredients. Manufacturers are still not required to make any statements on the packaging about potential side effects, nor are they required to prove that a supplement is safe or effective.

Side effects: The side effects of many dietary supplements have not been studied and are unknown. Megadosing with supplements that are generally safe at lower doses, however, may cause the supplement (if fat-soluble) to build up in the body and interfere with the absorption or metabolism of other supplements or pharmaceutical drugs. Botanicals may also change the way in which other drugs or supplements act in the body by speeding up or inhibiting their actions.

In addition, many natural plant substances (such as foxglove, hemlock, or ephedra) can be dangerous or life-threatening. According to the American Association of Poison Control Centers, in 2012 more than 4,800 people in the United States were treated in a health care facility because of ingesting dietary supplements, and two died.

Finally, dependence on dietary supplements to treat cancer or any serious disease may deprive the individual of effective traditional drugs and medical care that can save or prolong life. Individuals interested in taking dietary supplements as part of their cancer treatment regimen should research information carefully and discuss their findings with their oncologist before beginning a supplement.


Alschuler, Lise, and Karolyn A. Gazella. Alternative Medicine Magazine’s Definitive Guide to Cancer: An Integrated Approach to Prevention, Treatment, and Healing. Berkeley: Celestial Arts, 2007. Print.

Davis, W. Martin. Consumer’s Guide to Dietary Supplements and Alternative Medicines. Binghamton: Pharmaceutical Products, 2006. Print.

"Dietary Supplements." MedlinePlus. Natl. Lib. of Medicine, 1 Oct. 2014. Web. 2 Oct. 2014.

"Dietary Supplements: Background Information." Office of Dietary Supplements. Natl. Institutes of Health, 24 June 2011. Web. 2 Oct. 2014.

"FDA 101: Dietary Supplements." FDA. Food and Drug Administration, 7 Dec. 2013. Web. 2 Oct. 2014.

Micozzi, Marc S., ed. Complementary and Integrative Medicine in Cancer Care and Prevention: Foundation and Evidence-Based Interventions. New York: Springer, 2007. Print.

Quillin, Patrick. Beating Cancer with Nutrition. 4th ed. Tulsa: Nutrition Times, 2005. Print.

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