January 16, 2020
2 min read

Antioxidant supplements linked to increased risk for breast cancer recurrence, death

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Christine B. Ambrosone, PhD
Christine B. Ambrosone

Use of antioxidant supplements during chemotherapy, as well as iron and vitamin B12, by patients with breast cancer may increase their risk for disease recurrence and death, according to results of a prospective study published in Journal of Clinical Oncology.

“Although this is an observational study and the number of users of supplements was fairly small, the results are compelling,” Christine B. Ambrosone, PhD, chair of the department of cancer prevention and control at Roswell Park Comprehensive Cancer Center, said in a press release. “Patients using antioxidants before and during chemotherapy had an increased risk for their breast cancer returning and, to a lesser degree, had an increased risk [for] death. Vitamin B12, iron and omega-3 fatty acid use was also associated with poorer outcomes.”

Many patients with cancer use dietary supplements during treatment. However, few data exist on the efficacy and safety of these supplements to guide clinical recommendations for their use during chemotherapy. Further, because a cytotoxic mechanism of cancer therapeutics is through the generation of reactive oxygen species, concerns have been raised that dietary supplements, especially antioxidants, could reduce treatment efficacy, researchers noted.

Ambrosone and colleagues conducted the Diet, Exercise, Lifestyle and Cancer Prognosis (DELCaP) analysis, a correlative to the randomized phase 3 SWOG S0221 trial, to examine associations between use of supplements and breast cancer outcomes.

The trial included patients with breast cancer who had been randomly assigned to different treatment schedules with doxorubicin, cyclophosphamide and paclitaxel. The researchers asked participants to complete surveys on their use of supplements at randomization and completion of chemotherapy.

Of the 2,014 patients eligible for this portion of the study, 1,134 returned the surveys. Researchers indexed breast cancer recurrence and survival at 6 months after enrollment through a landmark approach.

Prevalence of supplement use, especially antioxidants, appeared low compared with published reports of use among patients with cancer, and tended to decrease during treatment, according to researchers.

Before treatment, 20.5% of patients used vitamin C. However, that decreased to 12.2% during therapy. Fewer than 10% of patients took both vitamin A and vitamin E during treatment, whereas 17.5% used at least one antioxidant. Additionally, 44% of patients took multivitamins during chemotherapy.

Results showed associations between use of any antioxidant supplement — including vitamin A, vitamin C and vitamin E, as well as carotenoids and coenzyme Q10 — before and during treatment and increased risk for breast cancer recurrence (adjusted HR [aHR] = 1.41; 95% CI, 0.98-2.04) and death (aHR = 1.4; 95% CI, 0.9-2.18).


An assessment of nonantioxidant supplement use showed patients who took vitamin B12 both before and during chemotherapy had significantly worse DFS (aHR = 1.83; 95% CI, 1.15-2.92) and OS (aHR = 2.04; 95% CI, 1.22-3.4).

Use of iron during chemotherapy appeared significantly associated with disease recurrence (aHR = 1.79; 95% CI, 1.2-2.67). This was true for use both before and during chemotherapy (aHR = 1.91; 95% CI, 0.98-3.7).

Omega-3 fatty acid use before and during treatment appeared associated with shorter DFS (aHR = 1.67; 95% CI, 1.12-2.49) but not OS.

Multivitamin use, meanwhile, did not impact survival outcomes.

“People diagnosed with any cancer should talk with their doctors about whether they should be taking vitamins or other supplements,” Ambrosone said. “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 chemotherapy.” – by John DeRosier

Disclosures: Ambrosone reports no relevant financial disclosures. Please see the study for all other authors’ relevant financial disclosures.