“Despite reported widespread use of dietary supplements during cancer treatment, few empirical data with regard to their safety or efficacy exist. Because of concerns that some supplements, particularly antioxidants, could reduce the cytotoxicity of chemotherapy, we conducted a prospective study ancillary to a therapeutic trial to evaluate associations between supplement use and breast cancer outcomes,” the researchers explained.
Breast cancer patients were randomized to cyclophosphamide, doxorubicin, and paclitaxel groups and answered questions about their supplement use at baseline and throughout the course of the trial. The researchers implemented Cox proportional hazards regression adjusting for clinical and lifestyle variables. Six-month recurrence and survival were recorded.
Dietary Supplements Affect Recurrence, Mortality Risks
A total of 1,134 patients were included in the study. The outcomes suggested that the use of antioxidant supplements—including vitamins A, C, and E; carotenoids; and coenzyme Q10—before and during treated increased the risk of recurrence (adjusted hazard ratio [aHR]=1.41; 95% confidence interval [CI], 0.98 to 2.04; P=0.06); mortality risk was also higher, but to a lesser degree (aHR=1.40; 95% CI, 0.90 to 2.18; P=0.14). Examining associations with individual antioxidants yielded weaker correlations, which the researchers surmised may be due to small numbers. When analyzing nonantioxidant supplements, the use of vitamin B12 before and during chemotherapy was correlated significantly with worse disease-free survival (aHR=1.83; 95% CI, 1.15 to 2.92; P<0.01) and overall survival (aHR=2.04; 95% CI, 1.22 to 3.40; P<0.01). Iron use during chemotherapy significantly increased recurrence risk (aHR=1.79; 95% CI, 1.20 to 2.67; P<0.01); use before and during treatment also increased recurrence risk (aHR=1.91; 95% CI, 0.98 to 3.70; P=0.06). Outcomes were similar for overall survival. No correlation was observed between multivitamin use and survival outcomes.
The study was published in the Journal of Clinical Oncology.
“Associations between survival outcomes and use of antioxidant and other dietary supplements both before and during chemotherapy are consistent with recommendations for caution among patients when considering the use of supplements, other than a multivitamin, during chemotherapy,” the study authors concluded.