Cancer patients who take antioxidant supplements could be blocking the process by which radiation and many chemotherapy agents kill tumours, new research has found.
Both forms of therapy work by inducing the creation of free radicals – destructive molecules which damage DNA and proteins.
Antioxidants also mop up free radicals, but supplements such as vitamin E and beta carotene could actually reduce the potency of anticancer treatments, according to researchers from the Naval Medical Centre in California.
Conversely, some experts believe that antioxidants may protect healthy tissues and reduce the side effects of cancer therapy.
Dr Brian Lawenda and colleagues reviewed the evidence from a number of trials and found that one large investigation into radiotherapy showed antioxidant supplements to be associated with lower survival rates.
In the case of chemotherapy, no trial reported a reduced response for patients taking antioxidants. However, none of the studies was sufficiently large enough to detect such differences, the researchers said.
“Despite some intriguing studies that have suggested the benefit of adjunctive antioxidant treatments in cancer patients, the totality of the evidence is equivocal at best and leaves us with serious concerns about the potential for harm,” said the scientists, writing in the Journal of the National Cancer Institute.
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