There is much debate whether or not antioxidant supplementation during cancer chemotherapy alters the efficacy of chemotherapy drugs. The review by Block et al. (2007), evaluating Randomized Clinical Trials (RCT), looks at RCTs that measured survival and/or treatment response levels of patients who took antioxidants while on chemotherapy in order to see if antioxidants amplify or impinge on the efficacy of the chemotherapy…
Block et al. (2007) start their review by citing no less than ten references about the use of Complementary and Alternative Medicine (CAM), showing that an estimated 13% to 87% of cancer patients use antioxidant supplements.
Antioxidants, while taken during chemotherapy are thought to
- a) hinder the cytotoxicity of chemotherapy by quenching the reactive oxygen species (ROS, a.k.a. free radicals), thus rendering the drug less effective, or
- b) help protect healthy cells from the onslaught of free radicals during chemotherapy (Block et al. (2007).
The Catch-22 for a cancer patient then is to understand if antioxidant therapy can improve Quality of Life (QoL) by protecting healthy tissue or gravely interfere with the outcome of cancer.
On the other hand, antioxidants might improve clinical outcomes by helping patients tolerate an uninterrupted treatment regimen with full doses of chemotherapy (Block et al., 2007).
Patients in the studies were either on an orally or intravenously administered antioxidants and chemotherapy. Block et al. (2007) make it clear that all types of cancers were included and chemotherapies that use ROS generating mechanism, while studies using whole herbs, multi-component herbals, and synthetic antioxidants were excluded. Trials were given Jadad scores to distinguish between weak and strong study designs. A limitation pointed out by Block et al. (2007) is the fact that “…bias in preferential publication of positive trials cannot be excluded” (p. 409).
Brief Overview of Outcomes
Out of 845 trials 19 were included in their review, using antioxidants Glutathione (7), Melatonin (4), Vitamin A (2), Mixed (2), Vitamin C (1), N-Acetylcysteine (1), Vitamin E (1), and Ellagic Acid (1).
Block et al. (2007) did not find any evidence that substantiated the concern that antioxidant supplementation given while on ROS generating chemotherapy lessened the efficacy of chemotherapy in a population of advanced or relapsed patients. On the contrary, 17 of the 19 reviews established
“…statistically significant advantage or non- significantly higher survival and/or treatment response in those patients given antioxidants. Specifically, of 13 reports on survival, all showed similar or better (four being statistically significant) survival rates for the antioxidant group over the control group” (Block et al., 2007, p. 415).
Block et al. (2007) continue with their findings:
“Additionally, while one study reported similar survival results between the antioxidant arm and control overall, the largest subgroup (stage III patients taking antioxidants) was found to have a statistically significant survival advantage compared to the control group” (p. 415).
And possibly the most reassuring statement:
“No studies reported significantly worse survival or response in the antioxidant supplement group” (Block et al., 2007, p. 415).
Limitations of the Block et al. (2007) Paper
Because of the small size of studies, these studies should be construed as treatment response data, and can’t be yet generalized to a wider population. Larger trials would be needed for such a generalization.
And because statistical power calculations performed either before or after trials, one can not say of important clinical effects were missed in these smaller trials.
The Bottom Line
This paper by Block et al. (2007) hints towards evidence that antioxidant supplementation helps reduce side effects of chemotherapy such as “…neurotoxicity, thrombocytopenia, diarrhea” (p. 416) and because of that, patients who probably would have dropped out of chemotherapy were able to complete their drug regimen.
Block et al. (2007) point to research by Neugut et al. (2006) studying colon cancer patients over age 65 and the effects of the entire five to seven months of chemotherapy regimen. These patients had higher survival rates than those who only received one to four months of treatment.
Also worthwhile considering is the finding that “…among the 30% of patients who dropped out of chemotherapy treatment early, mortality rates were twice those of the group who completed therapy” (Block et al. (2007, p. 416).
In other words, whether or not to use antioxidant supplementation during chemotherapy should probably be a conversation you and your primary care provider or oncologist should have.
However, just in case you are wondering going out to your local health food store to stock up on the antioxidants mentioned in this blog entry consider the following:
Block et al. (2007) clearly make mention of antioxidants administered intravenously, right? So this should give the reader pause and consider the dosages needed to achieve the desired effects.
Block, K. I., Koch, A. C., Mead, M. N., Tothy, P. K., Newman, R. A., & Gyllenhaal, C. (2007). Impact of antioxidant supplementation on chemotherapeutic efficacy: A systematic review of the evidence from randomized controlled trials. Cancer Treatment Reviews, 33(5), 407–418. doi: 10.1016/j.ctrv.2007.01.005
Neugut, A. I., Matasar, M., Wang, X., McBride, R., Jacobson, J. S., Tsai, W.-Y., Grann, V. R., et al. (2006). Duration of adjuvant chemotherapy for colon cancer and survival among the elderly. Journal of clinical oncology: official journal of the American Society of Clinical Oncology, 24(15), 2368–2375. doi:10.1200/JCO.2005.04.5005
Cancer the killer. (n.d.). Description: A comic book on the history of the disease and warning signs of cancer. Retrieved from the Images From The History Of Medicine website at http://ihm.nlm.nih.gov/luna/servlet/view/search?q=A024304
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APA: W Absenger. (2012.06.16). Block et al. (2007). Impact of antioxidant supplementation on chemotherapeutic efficacy [Web log post]. Retrieved from The Alternative Medicine Blog at http://amacf.org/2012/06/block-et-al-2007-impact-of-antioxidant-supplementation-on-chemotherapeutic-efficacy.html
MLA: Absenger, Werner. “Block et al. (2007). Impact of antioxidant supplementation on chemotherapeutic efficacy” The Alternative Medicine Blog. The Alternative Medicine Blog., 16 JUNE. 2012. Web. Insert your date of access here.