Antioxidant supplements do not appear to interfere with the efficacy of chemotherapy, supplementation may actually improve patients’ toleration of treatment and post-treatment outcomes in terms of tumor response and survival, according to an article in the May issue of Cancer Treatment Reviews.

The current analysis, titled “Impact of Antioxidant Supplementation on Chemotherapeutic Efficacy: A Systematic Review of the Evidence from Randomized Controlled Trials,” evaluated 845 articles from five scientific databases that examined the effects of natural antioxidant supplementation concurrent with chemotherapy.

Of the 845 studies, 19 met all evaluation criteria. These included use of randomized trials with a control group and reporting of treatment response and survival data. The 1,554 patients represented had a variety of cancer types, and most had advanced or relapsed disease. Some of the antioxidants used in trials included glutathione, vitamin A, vitamin C, vitamin E, ellagic acid, selenium and beta carotene.

All of the studies that included survival data showed similar or better survival rates for the antioxidant group than the control group. None of the trials supported the hypothesis that antioxidant supplements diminish the effectiveness of chemotherapy treatments.

All but one of the studies that reported treatment response showed similar or better response in the antioxidant group than in the control group; 15 of 17 trials that assessed chemotherapy toxicities, including diarrhea, weight loss, nerve damage and low blood counts, concluded that the antioxidant group had similar or lower rates of side effects than the control group.

The authors noted that reducing side effects may help patients avoid having to cut back on their chemotherapy dosing, interrupt scheduled treatments, or abandon treatment altogether. This in turn, is likely to favorably impact treatment outcomes. A recent study of a group of colon cancer patients indicated that those who completed their full prescribed schedules of chemotherapy had survival rates nearly double those of patients who abandoned their chemotherapy treatment prematurely.

“This review demonstrates that there is no scientific support for the blanket objection to using antioxidants during chemotherapy. In addition, it also appears that these supplements may help mitigate the side effects of chemotherapy,” said Keith I. Block, MD, lead author of the study and Medical Director of the Block Center for Integrative Cancer Treatment. “This is significant because it increases the likelihood that patients will be able to complete their treatment.”

Co-author Robert Newman, MD, Professor of Cancer Medicine at M. D. Anderson Cancer Center said, “This study, along with the evolving understanding of antioxidant-chemotherapy interactions, suggests that the previously held beliefs about interference do not pertain to clinical treatment.”