Vitamins 'affect cancer treatments'
Updated on 27 May 2008
Vitamins may reduce the effectiveness of cancer treatments, experts have warned.
Antioxidant supplements could block the process by which radiation and many chemotherapy agents kill tumours, said scientists.
Both forms of therapy work by inducing the creation of free radicals - destructive molecules which damage DNA and proteins.
Antioxidants mop up free radicals, which is generally beneficial to health. But supplements such as vitamin E and beta carotene may also reduce the potency of anticancer treatments, according to American researchers.
On the other hand, some experts believe antioxidants may protect health tissues and reduce the side effects of cancer therapy.
Dr Brian Lawenda, from the Naval Medical Centre in San Diego, California, and colleagues reviewed the evidence from a number of trials.
Of three randomly controlled radiotherapy studies, one large investigation showed that antioxidant supplements were associated with lower survival.
In the case of chemotherapy, no trial reported a reduced response for patients taking antioxidants. However, none of these studies was sufficiently large enough to detect such differences, said the researchers.
The scientists wrote in the Journal of the National Cancer Institute: "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."
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