J.S., a 55-year-old female, presented to her oncology clinic for her third cycle of chemotherapy. During a routine consultation, she mentioned that she had been taking antioxidant supplements (Vitamin C 1000 mg, Vitamin E 400 IU) daily, recommended by a friend, to “boost her immune system” and combat any chemotherapy side effects.
While antioxidant vitamins, such as Vitamin C and Vitamin E, are generally considered safe, their use (or potential overuse) during chemotherapy raised concerns for J.S’s oncology healthcare team.
What is chemotherapy?
Chemotherapy is a commonly used term for cancer treatments that do not involve surgery or radiation. Many chemotherapy drugs can be described as “cytotoxic” which translates directly to “toxic to living cells”. Cancer is a disease in which cells of the body undergo uncontrolled growth, harming the body. In cancer treatment, cytotoxic agents are used for their toxicity to kill these fast-growing cells. However, non-cancerous or “normal” cells are also at risk of experiencing toxicity, which can be manifested as side effects of chemotherapy, for example, hair loss, vomiting, diarrhea, and the development of mouth sores.
What are antioxidants?
Antioxidants are nutrients that help fight damage to our cells. The way that cells process oxygen results in the production of unstable molecules, called free radicals, which can damage our cells and DNA. Over time, a build-up of free radicals may lead to diseases, such as cancer. The body’s cells can repair or prevent free radical damage by naturally making antioxidant enzymes and consuming antioxidants from a variety of food sources. Some of these common antioxidants include Vitamin C, Vitamin E, and Selenium. Overall, antioxidants help protect our cells from the daily damages they face.
Considerations for Efficacy and Safety
Current research shows that the action of antioxidants may not translate into long-term benefits during cancer treatment. The side effects of antioxidants, including interactions, may be difficult to predict as there is no standardized dose or specific type(s) of antioxidant(s) that are recommended alongside the use of chemotherapy. On one hand, patients treated with chemotherapy that reduces the patient’s antioxidant levels may require antioxidant supplements after treatment. Antioxidant supplements may reduce the frequency and severity of side effects associated with chemotherapy. Therefore, it is possible that antioxidant use might facilitate the administration of higher and more effective doses of certain types of chemotherapy. However, it is important to note that within the context of different types/stages of cancers, various chemotherapy agents may have different effects and impacts on the antioxidant levels in a patient’s body. For example, Bortezomib, an anticancer medication that is used for multiple myeloma (cancer associated with a type of white blood cells), interacts with the antioxidant components in green tea, which may inhibit the therapeutic efficacy of Bortezomib, leading to ineffective cancer treatment.
What can J.S. do? Does she need to worry about Vitamin C and Vitamin E, etc. found in food?
As the recipient of care, patients should always consider the five questions to ask about their medications (see Figure 1)) during a clinical encounter with their healthcare providers. Patients should always be well informed of their medications, including vitamins, supplements, and natural health products. They can discuss and ask their pharmacist or healthcare team about their vitamins, supplements, and natural health products. This can help their healthcare team identify potential interactions and manage them appropriately.
With regards to J.S., her healthcare team discussed the possible interactions between high-dose antioxidants and chemotherapy; and advised her to stop the supplements. Dietary levels of antioxidants are considered safe during chemotherapy and cancer treatment. It is important to maintain a healthy and well-balanced diet. J.S. is recommended to focus on a balanced diet with natural antioxidants from fruits and vegetables, which will provide a safer, more moderate level of antioxidant activity without interfering with her cancer treatment.
By Fatima Hashemi-Sabet, Ziyi Xiao, Sheena Ye, Uroosa Abbas, and Certina Ho
Fatima Hashemi-Sabet, Ziyi Xiao, Sheena Ye, and Uroosa Abbas are PharmD students at the Leslie Dan Faculty of Pharmacy, University of Toronto; and Certina Ho is an Assistant Professor at the Department of Psychiatry and Leslie Dan Faculty of Pharmacy, University of Toronto.