Antioxidant Supplement Use During Chemo May Increase Risk for Breast Cancer Recurrence


This study provides data for consideration when discussing with patients the use of dietary supplements while undergoing chemotherapy.

The use of antioxidant supplements during chemotherapy, as well as iron and vitamin B12, may increase the risk of breast cancer recurrence and mortality in patients with breast cancer, according to a study published in the Journal of Clinical Oncology.1

The findings provide data for consideration when discussing with patients the use of dietary supplements while undergoing chemotherapy, however researchers cautioned that the results are not definitive enough to influence how doctors treat cancer patients. 

In this cohort of 1,134 patients with breast cancer who were randomly assigned to an intergroup metronomic trial of cyclophosphamide, doxorubicin, and paclitaxel, participants were queried on their use of supplements at registration and during treatment. Eighteen percent of the patients used at least 1 antioxidant daily, while 44% took multivitamins. 

The research indicated that use of any antioxidant supplement both before and during treatment was associated with an increased hazard of recurrence (adjusted hazard ratio [adjHR], 1.41; 95% CI, .98-2.04; P= .06) and, to a lesser extent, death (adjHR, 1.40; 95% CI, .90-2.18; = .14). 

“These findings of increased risk of poor outcomes with use of antioxidant supplements are congruent with concerns that use of antioxidants during chemotherapy could reduce the cytotoxic effects of (reactive oxygen species) generated by numerous chemotherapy agents and seem to support the recommendations by some that antioxidant supplements not be consumed during cancer therapy,” the authors wrote. 

In regard to individual antioxidants, relationships were weaker, potentially due to smaller numbers. For nonantioxidants, use of vitamin B12 both before and during chemotherapy was significantly associated with poorer disease-free survival (adjHR, 1.83; 95% CI, 1.15-2.92; < .01) and overall survival (adjHR, 2.04; 95% Ci, 1.22-3.40; P < .01). Additionally, iron use during chemotherapy was significantly associated with recurrence (adjHR, 1.70; 95% CI, 1.20-2.67; < .01) as was use both before and during treatment (adjHR, 1.91; 95% CI, 0.98-3.70; = .06). Similar results were presented for overall survival. Multivitamin use was not associated with survival outcomes. 

If patients are experiencing changes in taste or loss of appetite related to the effects of cancer treatment, possibly making whole vegetables, fruits, and grains unappealing or difficult to eat, they should seek out guidance from their medical team or dietician to discuss alternate ways to incorporate these foods into their diet, Christine B. Ambrosone, PhD, of Roswell Park Comprehensive Cancer Center, advised in a press release.

“People diagnosed with any cancer should talk with their doctors about whether they should be taking vitamins or other supplements,” Ambrosone, the lead investigator for the study, said in a press release.2 “I’d recommend that they try to get their vitamins and minerals – including antioxidants – through food. With a healthy and balanced diet, you can get all the nutrients your body needs, even while undergoing chemo.”

To evaluate a clearer correlation between breast cancer and antioxidant use during chemotherapy, researchers indicated that a larger, randomized trial testing groups who do and do not take supplements is necessary.

This study, titled the Diet, Exercise, Lifestyle and Cancer Prognosis (DELCaP) study, was correlated with a phase III trial led by SWOG (S0221). The pervasiveness of supplement use was previously reported in S0221, specifically in relation to recommendations from treating oncologists and in relation to chemotherapy-induced peripheral neuropathy (CIPN). 


1. Ambrosone CB, Zirpoli GR, Hutson AD, et al. Dietary Supplement Use During Chemotherapy and Survival Outcomes of Patients with Breast Cancer Enrolled in a Cooperative Group Clinical Trial (SWOG S0221). Journal of Clinical Oncology. doi:10.1200/JCO.19.01203.

2. Antioxidant Use During Chemotherapy Risky for Breast Cancer Patients [news release]. Portland, Oregon. Published December 19, 2019. Accessed January 14, 2020.

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