Cancer therapeutics may use the mechanism of generation of reactive oxygen species (ROS). Because of this, there has been thought that intake of vitamin supplements during cancer treatment, especially antioxidants, may counteract treatment [Lawenda BD, Kelly KM, Ladas EJ, et al, 2008 as cited in reference i]. Antioxidants include vitamins A, C, E, carotenoids, and coenzyme Q10.
Dietary Supplement Use During Chemotherapy and Survival Outcomes of Patients with Breast Cancer Enrolled in a Cooperative Group Clinical Trial (SWOG S0221)
Journal: Journal of Clinical Oncology
Over 1100 participants completed the Diet, Exercise, Lifestyle and Cancer Prognosis (DELCaP) study. Patients with breast cancer were asked to report use of supplementation before diagnosis, before treatment, and upon completion of chemotherapy. Outcomes included breast cancer recurrence and death. The authors defined disease-free survival as “among patients alive without recurrence at 6 months, the time from [6 months] until the first documentation of breast cancer recurrence, new breast cancer, or death, whichever came first” [i]. Overall survival was defined as “the time from 6 months after enrollment until death as a result of any other cause” [i].
The authors found:
1. Those that used any antioxidant before and during treatment were at increased risk of recurrence and, to a lesser degree, death
2. No association between use of antioxidants only before or only during treatment and survival outcomes
3. Non-significant associations between use of a single antioxidants and survival outcomes
4. No association between multivitamin or vitamin D use before, during, or both and survival outcomes
5. An association between use of vitamin B12 or iron before and during treatment and poorer disease-free survival and overall survival
6. An association between use of omega-3 fatty acids before and during treatment and poorer disease-free survival, but not overall survival
For the Patient and Caregiver
It is important to note that more evidence is needed in this area. Based on the present research, it may be recommended to avoid taking antioxidant supplements, iron, and vitamin B12 before and during breast cancer treatment. In this study, the omega-3 category included a variety of sources: fish oil, EPA, omega-3, flaxseed, and cod liver oil, and thus it is unclear which may have the association with survival outcomes.
For the Healthcare Team
Healthcare providers may recommend patients with breast cancer not take antioxidant supplements, iron, and vitamin B12 before and during treatment. The authors note that there was a small number of patients taking antioxidants, which reduced the statistical power to determine strengths of the associations found. Future research is called for in other cancers, as well as on the role that B12 and iron play with regards to decreasing response to cancer treatment. It will also be important to study how foods high in antioxidants influence treatment efficacy.
[i] Ambrosone CB, Zirpoli GR, Hutson AD, McCann SE, Barlow WE, Kelly KM, Cannioto R…Albain KS. (2019). 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: 37. doi: 10.1200/JCO.19.01203