Taking Antioxidants During Chemo Has Negative Effects

Roxanne Nelson, RN, BSN

December 20, 2019

Taking supplements while undergoing chemotherapy for breast cancer may not be such a good idea. A small study found that patients who took antioxidants, iron, vitamin B12, and/or omega-3 fatty acid supplements had worse outcomes than patients who did not.

Patients who reported the use of any antioxidant, including vitamins A, C, and E, as well as carotenoids and coenyzme Q10, were 41% more likely to experience disease recurrence if they used supplements both before and during chemotherapy treatment.

Patients taking vitamin B12, iron, and omega-3 fatty acid supplements were at a significantly greater risk for breast cancer recurrence and death.

However, the use of multivitamins did not affect outcomes either way.

"Although this is an observational study and the number of users of supplements was fairly small, the results are compelling," lead author Christine B. Ambrosone, PhD, chair of the Department of Cancer Prevention and Control at Roswell Park Comprehensive Cancer Center, Buffalo, New York, said in a statement.

"Patients using any antioxidant before and during chemotherapy had an increased risk of their breast cancer returning and, to a lesser degree, had an increased risk of death. Vitamin B12, iron, and omega-3 fatty acid use was also associated with poorer outcomes," she added.

The study was published online December 19 in the Journal of Clinical Oncology.

During the past 2 decades, a small but growing body of data has suggested that antioxidant supplements can be detrimental to cancer patients. Although the underlying mechanisms are unclear, some early research suggests that antioxidants may promote metastasis, at least in melanoma and lung cancer.

Higher Recurrence and Death

For the current study, Ambrosone and collegues used data from the Diet, Exercise, Lifestyle and Cancer Prognosis (DELCaP) study, a phase 3 trial led by SWOG (S0221) that randomly assigned breast cancer patients to receive various treatment regimens containing doxorubicin, cyclophosphamide, and paclitaxel. Participants were questioned about their use of supplements at two time points ― upon randomization and when treatment was completed.

A total of 1134 patients completed both questionnaires. Within this group, there were 251 recurrences and 181 deaths. Those who experienced disease recurrence or died were more likely to be older, to be postmenopausal, and to have a higher body mass index (all P < .05). They were also more likely to self-report as black (P = .10) and to have poor prognosis factors (four or more positive lymph nodes, estrogen receptor negativity, progesterone receptor negativity, human epidermal growth factor receptor 2 negativity; P < .01).

The authors comment that in comparison with previous reports in the literature, in this study, the use of supplements among patients was low and tended to decline during treatment. Only 17.5% of patients used any antioxidant during treatment (vitamins A, C, and E, carotenoids, or coenzyme Q10), and 44% took multivitamins.

Overall, patients who used any antioxidant both before and during treatment were at an increased risk for disease recurrence (adjusted hazard ratio, 1.41; P = .06) and, to a lesser degree, death (hazard ratio [HR], 1.40). No relationships were observed for use of antioxidants only before beginning treatment or only during chemotherapy.

For nonantioxidant supplements, there was no association between multivitamin and vitamin D use at any time point and outcomes.

However, "striking associations" were observed regarding vitamin B12 and iron supplements, the authors note. B12 supplementation was associated with worse disease-free survival (HR, 1.83) and overall survival (HR, 2.04) when used before and during treatment. Iron supplementation was associated with greater recurrence when taken during treatment (HR, 1.79) and when used both before and during chemotherapy (HR, 1.91), and similar relationships were observed with death. Taking omega-3 fatty acids both before and during treatment was associated with poorer disease-free survival (HR, 1.67) but not overall survival.

The authors note that as with many observational studies, the potential for bias exists, including selection, recall, and confounding biases. Although some researchers have reported that upward of 60% of cancer patients take antioxidant supplements during adjuvant treatment, that was not the case in the current study. The number of patients who took antioxidants and other supplements was fairly small, thereby reducing the statistical power.

"People diagnosed with any cancer should talk with their doctors about whether they should be taking vitamins or other supplements," said Ambrosone. "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."

The study was supported by grants from the Breast Cancer Research Foundation and the Roswell Park Comprehensive Cancer Center Cancer Center. The DELCaP trial was supported in part by the National Cancer Institute (NCI), Division of Cancer Prevention, SWOG NCI Community Oncology Research Program Research Base, the National Clinical Trials Network, and Amgen. Ambrosone has disclosed no relevant financial relationships. Several coauthors have disclosed relationships with industry, as detailed in the original article.

J Clin Oncol. Published online December 19, 2019. Abstract

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