Purpose: An estimated 45-80% of breast cancer patients use antioxidant supplements after diagnosis, and use of antioxidant supplements during breast cancer treatment is common. Dietary supplements with antioxidant effects include vitamins, minerals, phytonutrients, and other natural products. We conducted a comprehensive review of literature on the associations between antioxidant supplement use during breast cancer treatment and patient outcomes.
Methods: Inclusion criteria were: two or more subjects; clinical trial or observational study design; use of antioxidant supplements (vitamin C, vitamin E, antioxidant combinations, multivitamins, glutamine, glutathione, melatonin, or soy isoflavones) during chemotherapy, radiation therapy, and/or hormonal therapy for breast cancer as exposures; treatment toxicities, tumor response, recurrence, or survival as outcomes.
Results: We identified 22 articles that met those criteria. Their findings did not support any conclusions regarding the effects of individual antioxidant supplements during conventional breast cancer treatment on toxicities, tumor response, recurrence, or survival. A few studies suggested that antioxidant supplements might decrease side effects associated with treatment, including vitamin E for hot flashes due to hormonal therapy and glutamine for oral mucositis during chemotherapy. Underpowered trials suggest that melatonin may enhance tumor response during treatment.
Conclusion: The evidence is currently insufficient to inform clinician and patient guidelines on the use of antioxidant supplements during breast cancer treatment. Thus, well designed clinical trials and observational studies are needed to determine the short- and long-term effects of such agents.