Harm Shown from Antioxidants, Omega-3, and Certain Other Supplements During Chemotherapy

Taking Supplements During Breast Cancer Chemotherapy May Not Be a Good Idea. Journal of Clinical Oncology published a study on 19 December 2019 involving over a thousand patients. Antioxidant, iron, vitamin B12, and/or omega-3 supplement users had worse outcomes than nonusers.

Patients reporting antioxidants including vitamins A, C, E, carotenoids, and coenzyme Q10before and during chemotherapy were more likely to experience cancer recurrence (relapse) by % 41.

Vitamin B12, iron, and omega-3 fatty acid supplement users had significantly higher breast cancer recurrence and death risks.

Multivitamins, however, did not affect outcomes either way.

Any antioxidant use before and during chemotherapy increased recurrence and death risk. B12, iron, and omega-3 also correlated with worse outcomes.

Over the past twenty years, a small but growing evidence base suggests antioxidants may harm cancer patients (see previous studies on this topic). Mechanisms remain unclear, but early research suggests promotion of, at least in melanoma and lung cancer, metastasis .

Higher Recurrence and Death Rates

The study used data from breast cancer patients receiving doxorubicin, cyclophosphamide, and paclitaxel in various regimens through SWOG (S0221)’s phase 3 Diet, Exercise, Lifestyle, and Cancer Prognosis (DELCaP) trial. Participants were questioned about supplements at two separate timepoints: randomization and treatment completion.

Of 1134 completing both surveys, 251 had recurrence and 181 died. Those with recurrence or death tended to be older, postmenopausal, and have higher body mass index (BMI) . They also reported adverse prognostic factors: four or more positive nodes, estrogen and progesterone receptor negativity, and human epidermal growth factor receptor 2 negativity.

Compared with prior literature, use was low and declined during treatment. Only % 17.5 used antioxidants, vitamins A, C, E, carotenoids, or coenzyme Q10, during treatment, and% 44 reported multivitamins.

Use both before and during treatment correlated with higher recurrence and death risk. No association appeared for use before treatment alone or during chemotherapy alone.

No association appeared for non-antioxidant supplements, multivitamins, and vitamin D at any time. B12 before and during treatment correlated with worse disease-free survival. Iron during treatment or both before and during correlated with recurrence and death. Omega-3 before and during treatment correlated with worse disease-free but not overall survival.

As in observational research generally, selection, recall, and confounding biases may mislead. Some researchers report more than % 60 of patients use antioxidants during adjuvant (preventive) treatment, but not here. Few antioxidant and other supplement users reduced statistical power.

Support came from the Breast Cancer Research Foundation and Roswell Park Comprehensive Cancer Center. DELCaP was partly supported by the National Cancer Institute (NCI), Division of Cancer Prevention, SWOG NCI Community Oncology Research Program, National Clinical Trials Network, and Amgen.

Anyone diagnosed with cancer should discuss supplements with their doctor. Obtaining vitamins and minerals, including antioxidants, from foods is best. With a healthy, balanced diet you can obtain all necessary nutrients, even during chemotherapy.