Potential interactions between antioxidant vitamins and cancer chemotherapy

Current data show that approximately 50-65% of oncology patients are using complementary and alternative medicines - most commonly dietary therapy, megavitamins and relaxation/meditation. Although oncology patients may be using complementary medicines it is uncommon for these patients to inform their doctors or pharmacists, possibly due to fear of a negative response, or assumptions that complementary medicines will not interact with conventional treatment. To reduce the severity of adverse effects associated with chemotherapy some oncology patients may be advised to use antioxidants, in particular vitamins C, E and retinoids. The rationale behind this is that antioxidants neutralise the reactive oxygen species (ROS) produced by numerous chemotherapeutic agents. These ROS have been identified as the main cause of chemotherapy adverse effects, and therefore it is thought that antioxidants may prevent organ damage and reduce the severity of adverse effects. Incidentally, antioxidants have been studied for many years for their role in cancer chemoprevention and use. However, of far greater significance is the fact that these ROS may also contribute to the therapeutic effects of chemotherapy; even though the degree to which a particular agent relies on ROS for therapeutic efficacy is often unknown. Therefore antioxidant vitamins have the potential to interfere with cytotoxic effects of chemotherapy.