What to know about supplements and cancer

From vitamin A capsules to herbal teas and zinc tablets, dietary supplements come in all shapes and sizes. But are they a good fit for people with cancer?

Skyler Johnson, MD, researcher and assistant professor of radiation oncology at Huntsman Cancer Institute, Emily Preib, MS, RDN, CD, cancer dietitian in the Wellness and Integrative Health Center, and four oncology specialty pharmacy residents at the University of Utah share advice for choosing and using nutritional supplements safely.

What are dietary supplements?

Dietary supplements are a concentrated form of vitamins, herbs, minerals, or other nutrients designed to complement your diet and support your health. Some supplements help relieve side effects from cancer or cancer treatment. For example, calcium and vitamin D are often recommended to help with bone health.

However, not every claim made by supplement sellers is backed by data, and some products can even be harmful. Studies suggest that taking large amounts of antioxidants like vitamin C or vitamin E could make some treatments less effective. High doses of another antioxidant, beta-carotene, may increase the risk of developing certain cancers.

Why should I tell my cancer care team what I'm taking?

Whether they come from natural sources or are made in a lab, nutrients and drugs that enter the body must be broken down into forms that are easier to use, clear out, or both. Many cancer therapies and dietary supplements are processed using the same enzyme pathway. When supplements interact with cancer drugs in this pathway, treatment can become less effective or more toxic.

Timing can make a difference when taking supplements, as some cancer drugs take longer than others to be completely cleared from the body. Because many supplements and medications can interact, it is important to discuss everything you are taking— antioxidants, vitamins, probiotics, and herbal supplements—with your health care provider and decide on a plan that is safe for you.

How can I find out which supplements are safe to take?

If your doctor recommends taking a dietary supplement, ask your pharmacist or dietitian for help finding one that meets high quality and purity standards. Because herbs and dietary supplements are not monitored by the U.S. Food and Drug Administration, there is not as much data on their efficacy and safety.

However, there are organizations that provide voluntary quality testing and allow products to display a seal of quality assurance if they meet specific requirements. Checking for a stamp from US Pharmacopeia, NSF International, or ConsumerLab.com can help confirm that supplements are properly labeled and free of contaminants.

Are there other ways to stay healthy during cancer treatment?

Staying healthy and keeping blood counts within a safe range is important for continuing treatment. Eating a balanced diet, staying active, and trying mind-body therapies like meditation or yoga can help. Focusing on nutrition from food rather than supplements can also be beneficial.

A well-balanced diet should include plenty of fruits, vegetables, whole grains, beans and other legumes, nuts, and seeds. Plants and other whole foods contain safe levels of antioxidants and phytochemicals, both of which help the body fight inflammation and free radicals, unstable molecules that damage DNA and other cells. Getting enough protein is also important because the body needs protein to produce new blood cells. Over-the-counter supplements can be expensive and are often unnecessary if you are eating a nutritious diet.