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💊 Supplements and vitamins

What we know about supplements and when they can help or harm.

Nutritional supplements are among the most controversial topics in cancer care. Many patients take them out of a wish to do something extra for their health — which is understandable. But not all supplements are safe at every stage of treatment. Here is what we know and what specialists recommend.

When supplements can help

Documented nutritional deficiencies — vitamin D, iron, vitamin B12, zinc — should be corrected through supplementation, under a doctor's supervision. Liquid nutritional supplements (Ensure, Fresubin) can be useful when food intake is insufficient and there is no other solution. Omega-3s (EPA and DHA) have modest evidence for preventing loss of muscle mass in some patients, according to ESPEN.

The real risks of too many supplements

Vitamin C in high pharmacological doses can reduce the effectiveness of some chemotherapy drugs. High-dose beta-carotene has been linked to increased risk in smokers in some studies. Antioxidants in pharmacological doses can protect tumor cells from the effects of chemotherapy. Memorial Sloan Kettering maintains a detailed database (About Herbs, Botanicals & Other Products) of the known interactions between supplements and cancer medicines.

The basic rule: be open with your medical team

If you take, or plan to take, any supplement — including vitamin D, magnesium, curcumin, medicinal mushrooms or anything else promoted online — tell your oncologist or dietitian. Not all supplements are dangerous, but all of them need to be assessed in the context of your specific treatment. "Natural" does not automatically mean "safe".

Key points

What to remember from this article

✓Documented deficiencies (vitamin D, B12, iron) are corrected under medical supervision
✓High-dose antioxidants can interfere with chemotherapy
✓Always tell your oncologist which supplements you take
✓MSK has a public database of supplement–cancer drug interactions

Related practical guides

Concrete tips for similar situations

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How can I add more protein without eating much?

Compact protein sources for small portions.

Medical note

The information in this article is for guidance only and is based on international guidelines (ESPEN, Canadian Cancer Society, Memorial Sloan Kettering). It does not replace individualized medical advice. Discuss any nutrition decision with your medical team or an oncology nutritionist.

Sources

ESPEN Guidelines on Nutrition in Cancer Patients, 2021
Memorial Sloan Kettering Cancer Center – About Herbs, Botanicals & Other Products
Canadian Cancer Society – Vitamins and minerals

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