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Study Finds Antioxidants Risky During Breast Cancer Chemotherapy

woman sitting on couch looking at the label on her prescription bottle

Taking certain supplements while undergoing chemotherapy for breast cancer may do more harm than good. A small study found that patients who took antioxidants had higher chances of cancer recurrence and death. Taking a regular multivitamin, however, did not increase or decrease risk. The study was published online December 19, 2019 in the Journal of Clinical Oncology. It was led by researchers at the SWOG Cancer Research Network, funded by the National Cancer Institute.

Previous research has raised concerns that dietary supplements, especially antioxidants, can make chemotherapy less effective. This has led to doctors discouraging cancer patients from taking antioxidant supplements while they are undergoing chemotherapy. The new study is the first to look at supplement use during breast cancer treatment.

In this study, 1,134 patients undergoing chemotherapy for breast cancer answered questions about their supplement use. Researchers found those who reported taking any antioxidants – such as vitamins A, C, E, carotenoids, and Coenzyme Q10 – both before and during treatment were 41% more likely to have a cancer recurrence and 40% more likely to die. Taking antioxidants only before treatment or only during treatment did not affect risk of recurrence or death.

Eighteen percent of the people in the study used any type of antioxidant every day, and 44% took multivitamins. People who reported taking any antioxidant were 41% more likely to have their breast cancer return when they took the supplements both before and during chemotherapy treatment. Increased risk of recurrence and death were also observed for those who took vitamin B12, iron, and omega-3 fatty acid supplements. People who took multivitamins did not have any change in risk. 

Co-author Christine B. Ambrosone, PhD, says cancer patients should be cautious about taking supplements while in chemotherapy. "People diagnosed with any cancer should talk with their doctors about whether they should be taking vitamins or other supplements," she said in a statement. "I'd recommend that they try to get their vitamins and minerals - including antioxidants - from food. With a healthy and balanced diet, you can get all the nutrients your body needs, even while undergoing chemo."

Vegetables and fruits are rich sources of antioxidants. The American Cancer Society has long advised that cancer survivors eat a variety of vegetables and fruits every day. Patients and survivors should check with their doctor before taking any vitamins or supplements.

The American Cancer Society medical and editorial content team

Our team is made up of doctors and oncology certified nurses with deep knowledge of cancer care as well as editors and translators with extensive experience in medical writing.

Dietary Supplement Use During Chemotherapy and Survival Outcomes of Patients With Breast Cancer Enrolled in a Cooperative Group Clinical Trial (SWOG S0221). Published online December 19, 2019 in the Journal of Clinical Oncology. First author Christine B. Ambrosone, PhD, Roswell Park Comprehensive Cancer Center, Buffalo, NY.