By Mr. Voulgaris Evangelos, Pathological Oncologist, Scientific Head of the Department of Oncology and Chemotherapy of ANASSA Clinic
Taking “antioxidant” dietary supplements during chemotherapy for breast cancer may negatively affect the effectiveness of the treatment.
According to the study of the “Dietary Supplement Use During Chemotherapy and Survival Outcomes of Patients With Breast Cancer Enrolled in a Cooperative Group Clinical Trial (SWOG S0221)” published in the Journal of Clinical Oncology on December 19, 2019, breast cancer patients who took supplements of “antioxidants,” iron, vitamin B12 and/or omega-3 fatty acids before and during chemotherapy had worse outcomes than patients who did not.
Specifically, patients who reported using any “antioxidant,” including vitamins A, C, and E, as well as carotenoids and coenzyme Q10, were 41% more likely to have a recurrence of disease if they used supplements before and during chemotherapy. Patients who took supplements of vitamin B12, iron and omega-3 fatty acids were also at significantly higher risk of breast cancer recurrence and death. In contrast, the use of common multi-vitamin or vitamin D preparations did not appear to affect the therapeutic outcome.
Although this was an observational study and the number of patients was quite small (1134 patients), the results are very interesting. Over the last two decades, a growing body of data has suggested that “antioxidant” supplements may be harmful to cancer patients. Although the mechanism behind the observation is not yet clear, early research suggests that “antioxidants” may promote metastasis, at least in melanoma and lung cancer. The authors comment that compared with previous reports in the literature, in this study, supplement use among patients was low and tended to decrease 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 had an increased risk of disease recurrence and, to a lesser extent, death. Using antioxidants only before starting treatment or only during chemotherapy did not affect treatment effectiveness in this study; where “striking associations” were observed was in taking vitamin B12 and iron supplements, the researchers note. Taking B12 was associated with worse survival when used before and during treatment. Iron supplementation was associated with greater relapse and death rates when taken during treatment and when used both before and during chemotherapy.
As with many observational studies there is always an increased possibility of statistical error. Although according to the international literature over 60% of cancer patients receive ‘antioxidant’ supplements this was not the case in this study. The number of patients taking ‘antioxidants’ and other supplements was quite small, thus reducing statistical power.
A general rule of thumb that should be given to cancer patients (and which I at least apply faithfully to my own patients) is to try to get vitamins and minerals – including “antioxidants” – from food. In most cases with a healthy and balanced diet, the patient can get all the nutrients their body needs, even when undergoing chemotherapy. The indications for nutritional supplements are specific to oncology. In any case, people who have been diagnosed with cancer should talk to doctors about whether they should take vitamins or other nutritional supplements.