The use of antioxidant nutrients as a complement to standard cancer treatments has risen in popularity despite varying reports of their effectiveness. While a review of the clinical data suggests that antioxidant intake can have some influence on the efficacy and side effects of cancer therapy, the results are sometimes contradictory, making it difficult to give general recommendations. These discrepancies may be related to the type of cancer, the mechanism of action of the drugs used in treatment, and the type of antioxidants taken.
Two opposing views exist regarding the use of antioxidants taken during cancer treatment (chemotherapy and radiation). One view takes a complimentary approach utilizing antioxidant supplements to improve the efficacy and/or tolerability of standard therapies. The alternate view, which is held by most standard oncologists, recommends against taking nutritional supplements during cancer treatment because of the possibility that antioxidants might protect cancer cells from damage by cancer treatments.
Evidence Supporting the Use of Antioxidant Supplements During Cancer Treatment
Several nutrients have been shown to have a beneficial or synergistic effect when used in conjunction with cancer treatment. When taken together, supplementation of soy protein, vitamin E, and selenium has been demonstrated to slow the progression of prostate cancer when taken with prostate cancer treatments. Similarly, in a study of 370 patients with non-small-cell lung cancer or gastrointestinal cancer, melatonin combined with chemotherapy increased the rate of tumor regression and survival better than chemotherapy alone.
Multiple studies demonstrate that high doses of supplementary antioxidant nutrients (vitamins A, C, and E and carotenoids) improve the negative effect of radiation therapy on cancer cell growth, and in some cases also protect normal cells against collateral damage. NAC and vitamin E have also been reported to decrease the incidence of toxic hepatitis and the need for blood transfusions in patients being treated with chemotherapy and radiation therapy for acute lymphoblastic leukemia (ALL). Also, curcumin taken with radiation therapy has been shown to have a synergistic effect in reducing tumors in head and neck squamous cell cancer (HNSCC).
Overall, NAC, melatonin, and some flavonoids (found in berries, citrus, bananas, onions, parsley, black tea, green tea, red wine and dark chocolate) appear to be the most promising antioxidants for cancer therapies.
Variable Interactions of Antioxidants in Cancer Treatment
Alternately, in other studies the use of antioxidants has been shown to have a negative effect when taken together with cancer therapy. While high doses of vitamins C and E have been shown to improve side effects when administered with radiation for HNSCC, there is also evidence that they may decrease the effectiveness of the treatment.
Similarly, vitamin C taken with certain chemotherapy agents has been shown to decrease the antitumor action of the drug in the treatment of breast cancer and even to accelerate tumor growth when given with the chemotherapy agent, doxorubicin.
Clearly, more research is needed on this subject for patients to best be able to determine the pros and cons of taking antioxidant supplements during cancer treatment. A helpful recommendation is to always let your physician know about any nutritional supplements or botanicals you are taking during treatment for any medical condition.