A new report suggests that cancer patients should not take antioxidants because they appear to protect cancer tumours against chemotherapy and radiation.
A team of North American researchers analyzed data from clinical trials investigating the effects of antioxidant supplements in cancer patients undergoing chemotherapy and radiation.
They found that antioxidants seem to protect both healthy cells and cancer cells from the damage caused by the two treatments.
"Despite some intriguing studies that have suggested the benefit of adjunctive antioxidant treatments in cancer patients, the totality of the available evidence is equivocal at best and leaves us with serious concerns about the potential for harm," the report's authors wrote.
The commentary was published in the Journal of the National Cancer Institute.
Radiation and chemotherapy kill cells by creating free radicals, which damage the cells' DNA. Researchers have hypothesized that antioxidants can protect healthy cells and reduce the often debilitating side effects of treatment. But scientists have also wondered if taking supplements could protect cancer cells.
For this report, Dr. Brian D. Lawenda of the Naval Medical Center San Diego led his colleagues in the trial review.
In one of the trials that investigated antioxidants and radiation, supplements were linked with lower survival rates. However, smaller studies did not duplicate these findings.
Of the trials that analyzed the effect on chemotherapy, none could definitively demonstrate that antioxidants did not offer protection to tumour cells.
In a summary of their review, the authors concluded: "On the basis of our review of the published randomized clinical trials, we conclude that the use of supplemental antioxidants during chemotherapy and radiation therapy should be discouraged because of the possibility of tumour protection and reduced survival."
Commentary:
Should Supplemental Antioxidant Administration Be Avoided During Chemotherapy and Radiation Therapy?
Brian D. Lawenda, Kara M. Kelly, Elena J. Ladas, Stephen M. Sagar, Andrew Vickers, Jeffrey B. Blumberg
Despite nearly two decades of research investigating the use of dietary antioxidant supplementation during conventional chemotherapy and radiation therapy, controversy remains about the efficacy and safety of this complementary treatment. Several randomized clinical trials have demonstrated that the concurrent administration of antioxidants with chemotherapy or radiation therapy reduces treatment-related side effects. Some data indicate that antioxidants may protect tumour cells as well as healthy cells from oxidative damage generated by radiation therapy and some chemotherapeutic agents. However, other data suggest that antioxidants can protect normal tissues from chemotherapy- or radiation-induced damage without decreasing tumour control. We review some of the data regarding the putative benefits and potential risks of antioxidant supplementation concurrent with cytotoxic therapy. On the basis of our review of the published randomized clinical trials, we conclude that the use of supplemental antioxidants during chemotherapy and radiation therapy should be discouraged because of the possibility of tumour protection and reduced survival.'
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