Reviews Support Antioxidant Use during Chemotherapy
Antioxidants, Free Radicals & Cancer
Getting sufficient amounts of a certain antioxidant nutrients is believed to lower the risk of developing some cancers. Supplemental selenium and vitamin E, for example, have been shown to reduce the risk for prostate cancer in men, while diets high in vitamin A and beta carotene from fruits and vegetables seem to modestly reduce the risk of breast cancer in pre-menopausal women.
By mopping up free radicals, antioxidants help protect tissues from the effects of oxidation - a process that may help transform normal cells into pre-cancerous ones. Although the protective potential of antioxidants in cancer prevention is well recognized, the use of antioxidant supplements by patients undergoing cancer treatment has long been controversial.
Decade-Long Debate and Dilemma
For over a decade scientists have debated whether antioxidant supplementation during chemotherapy is good, bad or neutral. Some suggest that antioxidants may reduce the toxicity of certain chemotherapeutic drugs, allowing for uninterrupted treatment schedules and offsetting the need to reduce drug doses. Others argue that antioxidants could interfere with the effectiveness of chemotherapeutic drugs by scavenging the very free radicals many of these drugs produce to kill cancerous tumors.
These differing views present a dilemma for cancer patients trying to understand whether antioxidants will increase their quality of life by protecting healthy cells from the toxicity of their treatment, or whether these nutrients can interfere with the treatment itself and impede their clinical outcome. Now, two newly published reviews suggest that antioxidants do not hinder treatment effectiveness, and that they confer important benefits.
Review of Randomized Controlled Trials
Researchers from the University of Illinois at Chicago and the Institute of Integrative Cancer Research and Education teamed up to systematically review published trials evaluating the use of antioxidants with chemotherapy(1). Of the 845 papers found in the literature, the reviewers included only randomized, controlled clinical trials that reported patient survival time and/or tumor response - 19 trials in total. The antioxidants evaluated in those trials included vitamins A, C, E, antioxidant combinations, NAC and others. Most of the patients in these studies either had relapsed cancer or advanced disease.
No Negative Impact, Considerable Benefit
None of the trials included in the review provided evidence that antioxidants significantly affected treatment effectiveness. For the 17 studies that reported overall response to chemotherapy, 4 of them reported similar, and 13 reported better response rates for the antioxidant supplemented group compared to controls. Most importantly, no study reported worse survival or response in groups receiving these nutrients. In many of the studies, antioxidant supplementation resulted in fewer toxicities and either longer survival time, better tumor responses, or both.
The reviewers point out that cancer patients often have low levels of antioxidants before they undergo treatment. They concluded that antioxidants may help reduce the side-effects of chemo, that there's no scientific support for "blanket objections" to using antioxidants with chemotherapy, and that the use of antioxidants should be further explored in larger trials.
Confirmation and Caveats
These conclusions are echoed by the findings of another, though less rigorous, review conducted by oncologist Charles Simone MD and colleagues. Their evaluation of 50 human studies involving over 8,200 patients revealed that antioxidants decrease treatment side-effects and don't interfere with chemotherapy or radiation. Despite these positive reports, it's important to know that not all chemotherapy drugs work in the same way, and not all cancer cases are the same. So what's the bottom line? Anyone undergoing cancer treatment should discuss the use of antioxidants with their oncologist first, to determine what's best for them.
- Block K et al. Impact of antioxidant supplementation on chemotherapeutic efficacy: A systematic review of the evidence from randomized controlled trials. Cancer Treat Rev, doi:10.1016/j/ctrv.2007.01.005, Epub, 2007.
- Simone CB et al. Antioxidants and other nutrients do not interfere with chemotherapy or radiation and can increase kill and increase survival. Altern Ther Heath Med. 13:22-8 (Part I) and 13:40-7 (Part II), 2007.