The review could reignite the debate about potential benefits or risks, with some studies reporting that the supplements may have a detrimental effect. "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 lead author Keith Block, from the Institute for Integrative Cancer Research and Education and the University of Illinois. Antioxidants, such as vitamins A, C and E and carotenoids like beta-carotene, are believed to exert a protective effect on cells. They scavenge toxic molecules called free-radicals, which cause oxidative stress and can lead to DNA cell damage. "Much debate has arisen about whether antioxidant supplementation alters the efficacy of cancer chemotherapy," wrote Block in Cancer Treatment Reviews. "Some have argued that antioxidants scavenge the reactive oxygen species integral to the activity of certain chemotherapy drugs, thereby diminishing treatment efficacy. Others suggest antioxidants may mitigate toxicity and thus allow for uninterrupted treatment schedules and a reduced need for lowering chemotherapy doses." The researchers searched databases and identified 19 trials (1,554 participants) that met all evaluation criteria, including the use of randomized trials with a control group, and the reporting of treatment response (tumour shrinkage) and survival data. Block and his co-authors report that survival data showed similar or better survival rates for the antioxidant group than the control group, with none of the trials supporting the theory that antioxidant supplements diminish the effectiveness of chemotherapy. Additionally, 15 of 17 trials that assessed chemotherapy toxicities, including diarrhoea, weight loss, nerve damage and low blood counts, concluded that the antioxidant group suffered similar or lower rates of these 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 favourably impact treatment outcomes. "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," said co-author Robert Newman from M.D. Anderson Cancer Center. "The lack of negative impact of antioxidant supplementation on efficacy of ROS-generating chemotherapy in the studies reviewed, and the potential to diminish dose-limiting toxicity suggest that the clinical application of antioxidant supplementation during chemotherapy should be further explored," concluded the researchers. "Future research on concurrent use of antioxidants and chemotherapy should employ larger sample sizes and better research designs." Source: Cancer Treatment Reviews (Elsevier) May 2007, doi: 10.1016/j.ctrv.2007.01.005 "Impact of antioxidant supplementation on chemotherapeutic efficacy: A systematic review of the evidence from randomized controlled trials" Authors: K.I. Block, A.C. Koch, M.N. Mead, P.K. Tothy, R.A. Newman and C. Gyllenhaal
Antioxidants supplements may help increase cancer survival rates, tumour response, and the patient's ability to tolerate chemotherapy, concludes a new review.