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Vitamins & Cancer Treatment

Liz Puris, MS, RD, LDN
Dana-Farber Institute / Brigham and Women’s Cancer Center

Vitamins are often popular among oncology patients due to an increased interest in health. But what does research show regarding safety of vitamins both during and after cancer treatment? An Oncology Dietitian answers common patient questions.

Are vitamin deficiencies common?

Deficiencies are typically seen in specific patient populations such as older adults, those with restrictive diets, low socioeconomic status and poor access to nutrition, patients with alcoholism, malabsorption, or those with a history of certain surgical procedures such as gastric bypass.

Is a multivitamin safe to use during treatment?

In general, a multivitamin is safe to use during treatment. It is always best to make your care team aware of any vitamins or minerals you are taking, even if they are “natural” or “herbal.” Natural or herbal supplements have the potential to negatively interact with treatment. Many of the vitamins in a multivitamin are at much lower levels than would be sold individually. If taken in high doses, certain vitamins (such as fat-soluble vitamins A, D, E, K) can build up to harmful levels in the body.

What about Vitamin D?

Research has shown that people in certain geographical areas, such as the northern states, could benefit from a vitamin D supplement. Sunlight is the best source of vitamin D and these areas have limited amounts of light, especially in the winter. If you are concerned about a possible deficiency, your healthcare provider can do a blood test. Dose is important as well. Although moderate amounts of vitamin D may be beneficial, research is currently inconclusive on the effects of higher doses.

Are there any vitamins I should avoid during or after treatment?

The US Preventive Services Task Force (USPSTF) recommends against the use of both beta carotene or vitamin E supplements for the prevention of cancer. The US National Institutes of Health (NIH) states there is insufficient evidence to recommend the use or against the use of multivitamins for chronic disease prevention. A good reason to choose whole, plant-based foods as the best source for your vitamins and minerals!

What about antioxidant vitamin supplements? I’ve heard that antioxidants are good for patients with cancer.

Examples of antioxidants include vitamin A, vitamin C, vitamin E, beta carotene, lycopene, lutein, selenium, and manganese, among others. Although more research is needed, most facilities recommend against taking antioxidant vitamin supplements during both chemotherapy and radiation treatments. This is because the antioxidants can protect the cells “too much” and reduce the effectiveness of treatment. Antioxidants that come from whole foods, (think for example, of vitamin C from an orange) are generally considered safe and unlikely to interfere with treatment. This is because vitamin C in an orange is at a much lower “dose” and the fruit has many other vitamins and components to it such as fiber, compared to a high dose vitamin C supplement.

Are there certain brands of vitamins that are better than others?

While Dietitians do not endorse specific brands, we do recommend looking for third party testing labels to ensure a supplement’s label accurately represents the ingredients. Two examples of companies that provide independent testing are the NSF (National Sanitation Foundation) and USP (US Pharmacopeial Convention).

What is the bottom line regarding cancer and vitamins?

Every patient is different — diagnosis, treatment plan, age, medications, surgical history and risk factors, among others, will all affect vitamin and mineral requirements. Vitamin supplement research is ongoing, and it is best to prioritize obtaining your basic nutrient needs from whole food, plant-based sources. The more color in your diet, the more varied your vitamin and mineral intake will be. Benefits of colorful vitamins and minerals include helping to decrease cell damage as well as natural antioxidant, immune enhancing properties. And remember, for vitamin supplements, more isn’t necessarily better. Only in some cases, such as a vitamin deficiency, will patients need to take more than the recommended dosage specifically in pill form or by injection. Always ask your dietitian as well as your healthcare provider for specific recommendations related to your unique health needs.

  1. Dietary Supplements. Oncology Nutrition DPG.
    Published 2019. Accessed December 30, 2019.
  2. Fairfield KM. Vitamin supplementation in disease prevention. UpToDate.
    Published November 2019. Accessed December 30, 2019.
  3. American Cancer Society. Lifestyle Changes After Cancer Treatment: Nutrition and
    Physical Activity for Cancer Survivors After Treatment. 2016.