A clinical study in breast cancer patients evaluated the association of dietary supplement use before and during chemotherapy, and treatment outcomes. Surprisingly, use of antioxidant supplement (Vitamins A, C and E, carotenoids, coenzyme Q10) or non-oxidant supplements (Vitamin B12, iron) before and during treatment was associated with negative impact on treatment, recurrence and reduced overall survival.
A cancer diagnosis is a life-changing event associated with anxiety of the impending treatment journey and fear of the uncertainty of the outcome. After being diagnosed with cancer, patients are motivated to make life-style changes that they believe will improve their health and well being, reduce the risk of recurrence, and reduce the side-effects of their chemotherapy treatments. Often, they start using dietary supplements along with their chemotherapy treatments. There are reports of 67-87% of cancer patients that use dietary supplements post diagnosis. (Velicer CM et al, J Clin. Oncol., 2008) Given the high prevalence and widespread use of dietary supplements by cancer patients during their treatment, and concerns that some supplements, particularly antioxidants, could reduce the cytotoxicity of chemotherapy, it is important to understand the association of dietary supplement use during chemotherapy treatment on outcomes, including impact on chemotherapy-induced side-effects such as peripheral neuropathy.
As part of a large co-operative group therapeutic clinical trial to assess dosing regimens of DOX, cytophosphane (CP) and PTX, for treatment of high-risk breast cancer, a prospective ancillary trial was done to evaluate associations between supplement use and breast cancer outcomes. Diet, Exercise and Life-style (DELCap) Study based on a questionnaire was designed to examine life-style factors especially use of vitamin supplements before diagnosis and during chemotherapy in relation to treatment outcomes, as part of this therapeutic trial (SWOG 0221, NCT 00070564). (Zirpoli GR et al, J Natl. Cancer Inst., 2017; Ambrosone CB et al, J Clin. Oncol, 2019) There were 1,134 breast cancer patients who answered the questionnaires on their use of supplements prior to the start of treatment and during treatment, with a follow-up at 6 months after enrollment.
Key Findings of the Study Related to Dietary Supplement Use in Cancer
Summary of the key findings of the study related to association of dietary supplement use and treatment outcomes are:
- “Use of any antioxidant supplement (Vitamins A, C and E; carotenoids; coenzyme Q10) before and during treatment was associated with an increased hazard of recurrence (adjusted hazard ratio [adjHR[, 1.41; 95% CI, 0.98 to 2.04; P = 0.06)” (Ambrosone CB et al, J Clin Oncol., 2019)
- Use of non-antioxidants such as vitamin B12 before and during chemotherapy was significantly associated with poorer disease-free survival and overall survival (P<0.01).
- Use of iron supplement normally used to help with improving the anemia side-effect was significantly associated with recurrence, with use both before and during treatment. (P<0.01)
- Multivitamin use was not associated with survival outcomes.
- An earlier published analysis of the DELCap study indicated that the use of multivitamin before diagnosis was associated with reduced symptoms of chemotherapy induced peripheral neuropathy, however, use during treatment was not found to be beneficial. (Zirpoli GR et al, J Natl Cancer Inst., 2017)
The above data indicates that dietary supplements, vitamins and antioxidants, used by cancer patients post their diagnosis, and before and during their chemotherapy treatments, should be done thoughtfully and with caution. Even something as commonly and routinely used as antioxidants and multivitamins could have a potential of having a negative impact on treatment outcomes when used during the chemotherapy treatments.
Cancer patients often have to deal with different chemotherapy side effects which affect their quality of life and look out for alternative therapies for cancer. Taking the right nutrition and supplements based on scientific considerations (avoiding guesswork and random selection) is the best natural remedy for cancer and treatment related side-effects.