Do vitamin and mineral supplements affect the outcomes of chemotherapy in patients with breast cancer?

This study examined if patients with breast cancer that took different vitamin supplements before or during chemotherapy had poorer results from treatment. The results showed that anti-oxidants vitamin A, C, E, carotenoids and coenzyme Q10, as well as vitamin B12 and iron, negatively impact the outcomes of patients.

Breast cancer (BC) is often treated using chemotherapy. Chemotherapy kills cancer cells by producing chemicals called reactive oxygen species (ROS). Anti-oxidants, such as vitamins A, C, E, carotenoids and coenzyme Q10, destroy ROS. This normally improves health. However, it is unclear if it interferes with the action of chemotherapy. It is also unclear if other supplements, such as vitamin B, iron or a general multivitamin supplement, can also influence the effects of chemotherapy.

1134 patients with BC completed a questionnaire before and during chemotherapy. This questionnaire examined which supplements patients were taking. Patients were followed for an average of 8.1 months. 

17.6% of patients took an anti-oxidant supplement.  Patients who took an anti-oxidant supplement had a 41% higher risk of the cancer returning and a 40% higher risk of death. Vitamin C supplements increased the risk of cancer returning by 36%, vitamin E by 47% and coenzyme Q10 by 75%. Patients who took vitamin B12 supplements had an 83% lower survival without cancer and a 2.04 times higher risk of death.

Also, patients taking iron had a 79% higher risk of the cancer returning. Patients who took Omega 3 supplements also had a 67% higher risk of the cancer returning.

43.8% of patients took a multivitamin supplement. Patients who took multivitamin or vitamin D supplements did not have a higher risk of cancer returning or death.

The authors concluded that patients treated for breast cancer that took anti-oxidants, vitamin B12 or iron supplements during chemotherapy had a higher risk of the cancer returning or death. They also found that multivitamin supplements did not increase these risks.

This study was limited by the small number of patients that consumed some supplements. This study was also limited by its short follow-up of patients and did not take into account if some patients received other treatments such as radiotherapy. 

Talk to your doctor about the safety of vitamin or mineral supplements while receiving treatment.