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How to Use Supplements During Cancer Treatment

Navigating a cancer diagnosis and making critical decisions about your health may be overwhelming. When considering ways to help boost your immunity and wellness during this time, you may consider vitamin and herbal supplements. 

Each year, millions of Americans spend roughly $35 billion on supplements. Adding vitamins, minerals and other natural remedies like vitamins A, B, C, D and calcium may help fill nutritional gaps, but they may not help when you are undergoing cancer treatments. In some cases, certain supplements can be a danger to your health.

“People sometimes have more faith in ‘natural’ products or alternative therapies than traditional anticancer therapies, but they should really take extra care and discuss with their health care team,” said Helen Ross, MD, a thoracic medical oncologist with Banner MD Anderson Cancer Center at Banner Gateway Medical Center in Gilbert, AZ. “If a supplement interferes with cancer therapy or causes a complication, it may delay treatment or make treatment less effective.”

If you or a loved one are about to undergo cancer treatment, Dr. Ross shared what to know about supplements, which ones are safe and which ones to avoid.

What are supplements?

Supplements come in many forms, whether in pill, powder, gummies or liquid and contain at least one dietary ingredient, such as vitamins, minerals, herbs, botanicals, amino acids or enzymes. 

Some of the most popular supplements are multivitamins, which are a combination of vitamins, minerals and other ingredients. 

There are also herbal supplements that come from botanicals or plants, like echinacea, valerian root or St. John’s wort. Used for centuries, they are believed to have healing properties.

Do supplements really work?

“The biggest misconception is that we all need supplements,” Dr. Ross said. “The truth is unless you are pregnant or have a known history of a vitamin deficiency or are at risk for one, it’s best to get your nutrients from a balanced diet.”

Whether undergoing chemotherapy or not, the better, proven way to boost your health includes regular exercise and eating a diet rich in vegetables and fruits, complex carbohydrates, olive oil and high-quality protein. The Mediterranean diet is generally felt to be the best way to support the immune system and overall health.

[Check out “How to Eat Right When You’re in Treatment for Cancer.”]

“While diet alone isn’t felt to treat cancer, it can help with well-being,” Dr. Ross said. “High-fiber foods can manage constipation from treatments or supportive medications. Calorie-dense foods can help support weight when appetite is low from treatment.” 

Are supplements dangerous during cancer treatment?

If you are like many other people undergoing treatment, you want to throw a full-court press at your cancer – including supplements. 

The truth is that dietary supplements are not regulated by the U.S. Food and Drug Administration (FDA) because they are not classified as medication. This means you have no guarantee that your supplements contain only the ingredients on the label. 

Just because it says “natural” on the label, does not make it safe. Many people believe that any food or supplement in its natural form is better or safer, but some of the most toxic substances in the world are “natural.”

“Patients want to do everything they can to help treat their cancer and support their bodies and it can be tempting to look for the ‘miracle cure’ so they often focus on supplements, naturopathic treatments or homeopathy,” Dr. Ross said. “Some of these may be harmless, but many of them may interact badly with cancer treatments and decrease their effectiveness. Some can be harmful even on their own.”

Decreased treatment effectiveness: One negative way supplements can affect treatment is that they can counteract the effect of chemotherapy and radiation therapy. Many cancer treatments work by creating free radicals that work to destroy cancer cells. Taking certain supplements may counteract the oxygen free radicals and protect cancer cells, making treatments less effective.

Harmful interactions: Some dietary supplements, such as St. John’s wort, can potentially cause dangerous interactions and skin sensitivities with chemotherapy medications and radiation treatment.

Poorer outcomes:A recent study suggests that breast cancer patients who took supplements before and during treatment had worse outcomes,” Dr. Ross said. 

Antioxidant supplements like vitamins A, C and E were associated with a higher rate of cancer recurrence. Other vitamins like B12 and iron were associated with a negative effect on survival rates after cancer treatment.

What supplements are OK to take during treatment?

For the most part, supplements are not needed or should be avoided during treatment. However, there are special cases where your provider may prescribe supplements if you are undergoing chemotherapy treatments.

“For example, pemetrexed, a type of chemotherapy used to treat non-small cell lung cancers and malignant mesothelioma, requires supplementation with folic acid and vitamin B12 to prevent significant bone marrow toxicity, and bone strengthening medications such as zoledronic acid may require calcium and vitamin D supplementation,” Dr. Ross said. 

Vitamin D may also be taken if you are not getting outside in the sun or are not eating enough vitamin D-enriched foods. 

Ginger may help with nausea.

When should I talk to my provider?

Before you undergo cancer treatment, talk to your health care team. They can guide you on what is safe to use before, during and after cancer care.

“It’s important to have an open, honest discussion, so we can assess the risks and benefits together,” Dr. Ross said. 

Here are some suggested questions to discuss with your team:

  • Will my cancer treatment interact with any of my medications or supplements?
  • Will my cancer treatment interact with anything I eat or drink?
  • What supplements or over-the-counter medications are safe to take during treatment?
  • When will it be safe again to take medications and supplements?


Natural supplements may sound healthy – and many times they are – but they can be harmful if you are undergoing cancer treatment. Some may even counteract anti-cancer treatments.

Discuss any medications or supplements you are taking before you start treatment. Your health care team can guide you on what is safe to take before, during and after treatment.

Most often supplements are not necessary. Try to get your nutrition through a healthy diet. Your health care team can guide you on the right foods to eat.

If you ever have questions or concerns, your provider is there for you. To find a Banner MD Anderson specialist near you, visit bannerhealth.com. 

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