Diet and Nutrition

Dietary Supplements and Chemotherapy

January 11, 2017   /

When patients are undergoing cancer therapy, they may look for a simple solution to help them feel better, look better, enhance their immune system, tolerate their therapy more easily, or perhaps even treat their cancer. In many cases, they turn to dietary supplements.

Estimates report that 25%–80% of cancer survivors take supplements of some type. Dietary supplements (also called nutritional supplements) are defined as products that contain vitamins, minerals, herbs, or other botanicals, amino acids, enzymes, and/or other ingredients intended to supplement the diet. Because of the many different types of cancer, different cancer therapies, and different types of nutritional supplements, it is difficult to conduct research and to draw conclusions about the safety and efficacy of supplements during cancer treatment. Most of the research on the subject has focused on antioxidant nutrients, and the results are conflicting.

The majority of people perceive that dietary supplements are safe, natural, and inexpensive. By one estimate, 53% of individuals receiving chemotherapy do not discuss their supplement use with their health care provider. Even healthy people may face risks when taking dietary supplements, including interactions with medications. It does seem logical to attempt to treat nutrient deficiencies during cancer treatment with vitamin supplements. Some people choose to treat cancer with herbs or botanicals in addition to or in place of traditional treatment. However, lack of effectiveness and safety data, potential drug-nutrient interactions, quality control, and adulteration of nutritional supplements are all issues of concern for patients undergoing cancer treatment.

Little evidence exists to show that vitamin supplements can reproduce the benefits of a nutrient-rich diet. Many experts agree that using dietary supplements, particularly antioxidant supplements, especially in high doses during chemotherapy generally is not recommended. The same is true for other vitamin and mineral supplements and herbal or botanical treatments. Some experts suggest that a multivitamin containing 100% of the Dietary Reference Intakes (DRIs) is safe, but others express concern that dietary supplements can have cancer-promoting effects. Adverse effects associated with herbal supplements include risk of excessive bleeding, increase in blood pressure, and interactions with hormones or medications.

According to Deng et al, “It is recommended that dietary supplements, including botanicals and megadoses of vitamins and minerals, be evaluated for possible side effects and potential interactions with other drugs. Those that are likely to interfere adversely with other drugs, including chemotherapeutic agents, should not be used concurrently with immunotherapy, chemotherapy, or radiation or prior to surgery.”

Some situations might indicate the need for a multivitamin, such as when food intake is very poor or when a known condition requires supplementation (eg, bone loss requiring vitamin D and/or calcium, or folate for women of childbearing age).

Implications for dietetics practitioners
It is recommended that a trained professional evaluate patient use of dietary supplements, both prior to the start of cancer treatments and during the treatments. Dietitians should make sure to include information about the use of dietary supplements of all types during nutrition assessment of cancer patients.

They also should consider the need for a multivitamin in the overall context of a patient’s eating habits, lifestyle, use of oral nutritional supplements such as Ensure®, and treatment plan. If a patient desires to take a vitamin supplement or one is necessary because of inadequate intake, the amount should not to exceed the Upper Intake Levels (UL) of the DRIs for supplements containing antioxidant nutrients.


References and recommended readings
Academy of Nutrition and Dietetics. Nutrition Care Manual®. Available to subscribers at: Accessed February 22, 2012.

American Cancer Society®. Dietary supplements: how to know what is safe. Available at: Accessed February 22, 2012.

Deng GE, Frenkel M, Cohen L, et al. Evidence-based clinical practice guidelines for integrative oncology: complementary therapies and botanicals. J Soc Integr Oncol [serial online]. 2009;7:85-120. Available at: Accessed February 22, 2012.

Doyle C, Kushi LH, Byers T, et al. Nutrition and physical activity during and after cancer treatment: an American Cancer Society Guide for informed choices. CA Cancer J Clin [serial online]. 2006;56:323-353. Available at: Accessed February 22, 2012.

Mahan LK, Escott-Stump S, Raymond JL. Krause’s Food and the Nutrition Care Process. 13th ed. St Louis, MO: Elsevier Saunders; 2012:832-883.

National Institutes of Health, Office of Dietary Supplements. Dietary supplements: what you need to know. Available at: Accessed February 7, 2012.