Many people with cancer turn to antioxidant supplements hoping they can boost recovery, strengthen the immune system, or improve treatment outcomes. At the same time, some may have heard the claim that antioxidants can “feed” cancer cells, leading to confusion about whether they should be taken or avoided. The truth is that there is no strong evidence that antioxidants feed cancer. However, high-dose antioxidant supplements are generally not recommended during active cancer treatment, as they may interfere with the way certain chemotherapy drugs and radiotherapy work (Woldeselassie & Tamene, 2024).
Why are High-Dose Antioxidant Supplements Not Recommended?
Some cancer treatments, including chemotherapy and radiotherapy, work by generating oxidative stress to damage and destroy cancer cells. It has been proposed that taking high-dose antioxidant supplements during treatment may reduce this effect and potentially lessen the effectiveness of these therapies. Therefore, many cancer organisations advise patients not to take high-dose antioxidant supplements during active treatment unless recommended by their healthcare professionals.
For example:
- High-dose vitamin C infusions have not been shown to improve cancer treatment and may reduce the effectiveness of certain chemotherapy drugs (Mussa et al., 2022).
- Vitamin E supplementation may increase bleeding risk in some patients and may interact with certain treatments (Kaye et al., 2025).
- Green tea extracts, although rich in antioxidants, have been linked with rare cases of liver injury and may interfere with some medications (Grajecki et al., 2022).
Importantly, this does not mean antioxidants “feed” cancer. Rather, some supplements may alter how certain cancer treatments work.
Antioxidants from Food vs Supplements
A common misconception is that foods rich in antioxidants should also be avoided during cancer treatment. Fortunately, research does not support this idea. Whole foods contain hundreds of naturally occurring compounds, including vitamins, minerals, fiber, and phytochemicals that work together in ways supplements cannot replicate. Large observational studies consistently show that people who consume more fruits, vegetables, legumes and whole grains generally have better long-term health outcomes. By contrast, supplements often provide isolated nutrients at doses many times higher than dietary intake. Current dietary guidelines for cancer survivors continue to encourage a plant-rich eating pattern rather than relying on supplements for antioxidant intake.
Food first. Supplements only when medically indicated.
Which Supplements are Generally Considered Appropriate?
Not every supplement is harmful or unnecessary. Some patients may need supplements because of nutritional deficiencies, treatment side effects, poor appetite, or difficulty absorbing nutrients. Supplements should only be taken when there is a clear medical need and under the guidance of a healthcare professional.
Examples include:
- Vitamin D
Many people with cancer have low vitamin D levels due to limited sun exposure, poor dietary intake, or treatment-related factors. Supplementation may be recommended after blood testing under medical supervision (Kennel et al., 2010).
- Calcium
Certain cancer treatments, such as hormone therapy for breast or prostate cancer, can accelerate bone loss and increase the risk of osteoporosis. Calcium supplements may be recommended if dietary intake is insufficient or patients are at increased risk of weakened bones (Datta & Schwartz, 2013).
- Vitamin B12
Some cancer patients, particularly those who have undergone surgery involving the stomach or intestines, have digestive disorders that reduce nutrient absorption, or follow a strict vegetarian or vegan diet may be at risk of vitamin B12 deficiency. Supplementation may be needed to prevent anaemia and nerve damage (Ankar & Kumar, 2024).
- Omega-3 fatty acids
People who undergoing cancer treatment experience poor appetite, unintentional weight loss, or cancer cachexia, making it difficult to meet their nutritional needs. In selected patients, omega-3 supplements may be recommended as part of a nutrition care plan (Chua et al., 2024).
- Oral nutrition supplements
Oral nutrition supplements are specially formulated drinks or powders that provide energy, protein, vitamins, and minerals for people who are unable to meet their nutritional needs through food alone. They may be recommended for patients who experience poor appetite, difficulty chewing or swallowing, nausea, or unintentional weight loss during cancer treatment (Chen et al., 2023).
Building an Antioxidant-Rich Diet Safely
There is no single “superfood” that prevents or cures cancer. A varied, balanced diet provides a wide spectrum of beneficial nutrients that work together to support overall health during and after treatment.
Aim to include:
- A variety of colourful vegetables every day
- Fresh fruits such as berries, oranges, kiwi and papaya
- Tomatoes and tomato-based dishes
- Whole grains
- Beans and lentils
- Nuts and seeds
- Green leafy vegetables
- Healthy fats such as olive oil
- Fish several times each week when appropriate
Summary
Based on current scientific evidence, there is no proof that antioxidant supplements “feed” cancer cells. However, some high-dose antioxidant supplements may interfere with certain chemotherapy drugs or radiotherapy, and their routine use during active cancer treatment is not recommended unless advised by healthcare professionals. For most patients, the safest approach is to obtain antioxidants through a healthy, balanced diet rather than high-dose supplements. Before taking any vitamin, herbal product or antioxidant supplement, discuss it with your oncologist or oncology dietitian. Even natural products can interact with cancer treatments. The goal is not to avoid antioxidants, but to use them wisely, based on evidence rather than myths.
References
- Woldeselassie, M., & Tamene, A. (2024). Therapeutic controversies over use of antioxidant supplements during cancer treatment: a scoping review. Frontiers in Nutrition, 11, 1480780. https://doi.org/10.3389/fnut.2024.1480780
- Mussa, A., Idris, R. a. M., Ahmed, N., Ahmad, S., Murtadha, A. H., Din, T. a. D. a. a. T., Yean, C. Y., Rahman, W. F. W. A., Lazim, N. M., Uskoković, V., Hajissa, K., Mokhtar, N. F., Mohamud, R., & Hassan, R. (2022). High-Dose vitamin C for cancer therapy. Pharmaceuticals, 15(6), 711. https://doi.org/10.3390/ph15060711
- Kaye, A. D., Thomassen, A. S., Mashaw, S. A., MacDonald, E. M., Waguespack, A., Hickey, L., Singh, A., Gungor, D., Kallurkar, A., Kaye, A. M., Shekoohi, S., & Varrassi, G. (2025). Vitamin E (Α-Tocopherol): emerging clinical role and adverse risks of supplementation in adults. Cureus, 17(2), e78679. https://doi.org/10.7759/cureus.78679
- Grajecki, D., Ogica, A., Boenisch, O., Hübener, P., & Kluge, S. (2022). Green tea extract–associated acute liver injury: Case report and review. Clinical Liver Disease, 20(6), 181–187. https://doi.org/10.1002/cld.1254
- Kennel, K. A., Drake, M. T., & Hurley, D. L. (2010). Vitamin D deficiency in adults: When to test and how to treat. Mayo Clinic Proceedings, 85(8), 752–758. https://doi.org/10.4065/mcp.2010.0138
- Datta, M., & Schwartz, G. G. (2013). Calcium and vitamin D supplementation and loss of bone mineral density in women undergoing breast cancer therapy. Critical Reviews in Oncology/Hematology, 88(3), 613–624. https://doi.org/10.1016/j.critrevonc.2013.07.002
- Ankar, A., & Kumar, A. (2024, September 10). Vitamin B12 deficiency. StatPearls – NCBI Bookshelf. https://www.ncbi.nlm.nih.gov/books/NBK441923/
- Chua, A. V., Hernandez, A. R. B., Mendoza, M. J. L., & Juan, M. D. S. (2024). Omega-3 fatty acids increase weight and quality of life Scores in patients with Advanced Non-Small Cell Lung cancer and cancer Cachexia: A Meta-Analysis. Integrative Cancer Therapies, 23, 15347354241275052. https://doi.org/10.1177/15347354241275052
- Chen, Y., Lee, C., Chen, J., Ding, M., Liang, F., & Yang, S. (2023). Beneficial effects of oral nutrition supplements on the nutritional status and physical performance of older nursing home residents at risk of malnutrition. Nutrients, 15(19), 4291. https://doi.org/10.3390/nu15194291
