You've asked a difficult question. This issue has been generating a heated controversy, especially among cancer specialists (oncologists) who also practice integrative medicine.
One camp holds that taking antioxidants during cancer treatment could interfere with the way chemo and radiation work and diminish their benefits to the patient. This is because radiation and some chemotherapy agents work by generating free radicals, which then kill rapidly dividing cancer cells. Since antioxidants scavenge free radicals, they might interfere with the therapeutic effects of these treatments.
The opposing argument is that oxidation supports the proliferation of malignant cells and may itself interfere with treatment. People who hold this view maintain that antioxidants may counter the harmful effects of oxidation in the malignant process and thereby increase the effects of drugs or radiation therapy to the benefit of the patient. Moreover, they note that some evidence suggests that antioxidant supplements offer patients protection from the toxic effects of therapy.
As things now stand, we need more research before we can confidently advise patients one way or another. However, I posed your question to Donald Abrams, M.D., an integrative oncologist at the University of San Francisco and a graduate of the associate fellowship at the Program on Integrative Medicine here at the University of Arizona. Dr. Abrams told me that questions about antioxidants are the most frequent ones he gets. In the absence of strong evidence, he now advises patients as follows:
- For those being treated for a possible cure (meaning that their tumors have been removed and that the goal of chemotherapy or radiation is to destroy any remaining cancer cells): Don't take antioxidant supplements on the day before, the day of, and the day after chemotherapy. Otherwise, it is okay to take supplements.
- For patients undergoing radiation therapy: no antioxidant supplements throughout the course of treatment.
- For patients with advanced cancer who are being treated in order to prolong survival and relieve symptoms: it is okay to take antioxidant supplements. Because chemotherapy agents differ in their mode of action, it would be helpful to know whether the particular drugs being used work by an oxidative (free-radical-generating) mechanism. Ask the medical oncologist treating you for that information.
By the way, there is no justification for telling patients undergoing chemotherapy or radiation therapy to avoid antioxidant-rich foods.
Andrew Weil, M.D.