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Researchers at Roswell Park Comprehensive Cancer Center in Buffalo, N.Y., followed 1,134 breast cancer patients. The six-year study was part of a Phase 3 clinical trial to determine the best dose and schedule for three chemotherapy drugs in high-risk, early-stage breast cancer.

As part of the research, participants filled in surveys about their use of supplements before and during chemotherapy, as well as their lifestyle, diet and exercise habits.

Among the 18 per cent who took vitamins like A, C or E, all of which are antioxidants, their risk of the cancer returning was 40 per cent higher than the participants who didn’t take supplements.