Dietary Supplements and Cancer

Mesothelioma patients commonly turn to dietary supplements to help their body cope with cancer and recover from side effects of cancer treatment. It is important to talk to your oncologist about supplementation to avoid any negative interactions with your treatment plan.

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Dietary supplements are any vitamin, mineral, protein, enzyme, probiotic, herb or plant substance taken to supplement dietary needs or boost body functions. Supplements often come in the form of pills, powders and liquids that are ingested. Some supplements may be injected.

Doctors recommend or prescribe supplements when a patient is low or deficient in a certain essential nutrient. For example, when a patient’s blood test results indicate a deficiency in vitamin D or B12, a doctor will recommend they temporarily take a supplement to return their levels back to normal.

Some people have inheritable conditions that require them to regularly take a supplement throughout their lifetime, but in general, when a doctor recommends supplementation it is temporary and specific.

An exception is a multivitamin supplement. Many general practitioner doctors recommend a multivitamin because so few people follow a healthy diet that naturally provides the full range of dietary needs. Some people take these daily, while others take them occasionally such as once a week.

Unless your doctor tells you to take a particular supplement, it is safer to generally avoid them and opt instead for a healthy diet to provide the nutrients you need. Eating a diet rich in vegetables and fruits can reduce your cancer risk and help cancer patients cope with treatment, but no supplement has been scientifically proven to prevent or cure cancer among the general population.

Chemotherapy patients may be told to take certain supplements to reduce side effects. For example, mesothelioma patients on pemetrexed and cisplatin are told to take folate and B12 before and during treatment.

Additionally, oncologists may recommend a multivitamin or nutritional drink — such as Boost or Ensure — to cancer patients experiencing difficulty eating or swallowing. Chemotherapy and other cancer treatments can lessen appetite and disrupt digestion, making it difficult to get the nutrition you need to recover from treatment.

Are Supplements Safe for Cancer Patients?

Only your oncologist can decide if a supplement is safe to take, because each case of cancer is different and each person has a unique makeup.

Blood tests are the only way to tell if you are low in a certain nutrient. If your doctor orders nutritional testing of your blood and the results indicate you are low or deficient in a particular nutrient, your doctor will prescribe a specific nutritional supplement.

In general, cancer patients are not recommended to take supplements without consulting their oncologist first. Patients may unintentionally take a supplement that interferes with their cancer treatment.

These supplements may interfere with cancer treatment or lead to complications:

  • Vitamin C: This vitamin can protect cells from chemotherapy in ways that reduce the effectiveness of the treatment. Studies show vitamin C reduced effectiveness of chemotherapy by 30 to 70 percent.
  • Coenzyme Q10: This antioxidant may reduce effectiveness of chemotherapy and radiation therapy.
  • Turmeric: Also referred to as curcumin, this root is known to decrease or increase the effects of chemotherapy — and the increase can be toxic.
  • Acidophilus: This probiotic may promote infection if taken during chemotherapy.
  • Fish Oil: Patients with a low platelet count should avoid fish oil because it may induce bleeding. It may also interfere with chemotherapy.
  • Ginger Root: Ginger may also lead to bleeding.
  • Grapefruit: Eating grapefruit or drinking grapefruit juice blocks an enzyme in the intestine that helps metabolize certain mesothelioma chemotherapy drugs, including vincristine and paclitaxel.

There is a consensus among oncologists that antioxidants block the full potential of anti-cancer therapies.

Antioxidants protect our cells from damage and even help with cellular repair and recovery, which is important after cancer treatment. But it should be avoided during treatment to maintain drug effectiveness.

Specific antioxidants that concern oncologists include coenzyme Q10, selenium and the vitamins A, C and E. Vitamins A and E are of particular concern because studies done within the last decade in France and England show strong evidence they may actually drive cancer progression.

Other supplements are less cut and dry. Research shows the omega-3 fatty acids in fish oil help curtail weight loss among cancer patients, but fish oil reduces the effect of chemotherapy and increases risk of bleeding among patients with low platelet counts. Beta glucans are sugars that help the immune system fight certain cancers, but lab research shows they can promote the growth of leukemia cells.

It does appear to be safer to get nutrients through a healthy diet than supplementation. For example, eating foods high in beta carotene — such as carrots and tomatoes — reduce the risk of lung cancer, but taking beta carotene supplements does not have the same impact.

People with a history of asbestos exposure may reduce their risk of developing mesothelioma by consuming fruits and vegetables.

Researchers are investigating the potential benefit of certain traditional Chinese medicine herbs in combination with chemotherapy, including the mesothelioma chemotherapy drug gemcitabine.

Mesothelioma patients who are considering dietary supplements as a complementary or alternative therapy should consult their oncologist first. Mesothelioma Guide

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Risks and Side Effects

The U.S. Food and Drug Administration (FDA) tracks side effects of supplements, and their data shows people are increasingly reporting cases of illness and injury from supplementation.

From 2010 to 2012, reports of adverse events from dietary supplements more than doubled:

  • 2010: 1,009 reports
  • 2011: 2,047 reports
  • 2012: 2,844 reports

Risks and side effects of taking dietary supplements may include:

  • Exposure to supplements contaminated with toxic chemicals
  • Consuming supplements containing none of the listed ingredients
  • Reduced effectiveness of chemotherapy, radiation therapy and other anti-cancer drugs
  • Increased effectiveness of chemotherapy to the point of toxicity
  • Increased skin sensitivity, which may harm radiation therapy patients
  • Liver damage from certain herbs such as kava root and comfrey

Overdosing vitamin A may cause headaches, reduced bone strength, liver damage and birth defects. Excess iron may lead to nausea and vomiting and could damage the liver and other organs. Vitamin K interferes with the blood thinner warfarin (Coumadin).

Deceptive Advertising and Claims

People with mesothelioma should be extra cautious when hearing about claims of cancer cures coming from any supplement or natural product. Many of these claims are found online or through friends and family and are based on anecdotal evidence rather than scientific evidence.

Anecdotal evidence is based on personal accounts rather than facts or trustworthy scientific research.

In 2017, the FDA issued warning letters to 14 companies for fraudulently claiming their products could prevent, diagnose or cure cancer. A company producing Essiac Tea was among the group.

Supplement makers are not currently required to get FDA approval to sell their products. The FDA does investigate potentially harmful natural products, but the agency can only do this once the product is on the market.

In general, it is wise to assume if a claim seems too good to be true, it probably isn’t. Remain doubtful if a supplement claims to produce the same results as a prescription drug or cancer treatment.

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Common Misconceptions of Supplements

There are some common misconceptions around supplements and natural products.

Natural Is Better, Safer

The term “all natural” has become a buzzword in the health industry in response to people having adverse reactions to man-made chemicals and products made in a lab or factory.

While this conception is totally understandable and sometimes true, it should be weighed with the understanding that many natural substances can be harmful, too. For example, arsenic is naturally occurring and poisonous. There are a number of poisonous plants including oleander and tobacco. Natural is not always better or safer in every case.

Taking a Megadose of Vitamins Is Safe

Around the 1990s it became popular to megadose, or take large amounts, of certain supplements such as vitamins C and E.

Some people believed large doses of vitamin C could cure the common cold. While high doses of vitamin C have been studied as a potential cancer treatment since the 1970s, research does not indicate it can cure any cancer. In fact, taking too much vitamin C can block your body’s ability to absorb copper, an essential trace mineral involved in making red blood cells.

It Can’t Hurt to Take Supplements with My Medicine

Unfortunately, some supplements have negative interactions with prescription medication and cancer treatment. It isn’t safe to assume that any herb, vitamin or mineral won’t interact with your medication or cancer treatment just because they are natural or seemingly harmless.

Additionally, few drug companies or supplement producers research potential interactions, and this fact leads to consumers becoming the guinea pigs.

The FDA Won’t Allow It on the Market if It Isn’t Safe

Dietary supplements are regulated differently than prescription drugs and cancer treatments. Unlike pharmaceuticals and anti-cancer treatments, supplements do not undergo years of testing before reaching the market.

Consult Your Doctor

Mesothelioma patients are encouraged to discuss supplementation with their oncologist before taking any supplement or natural product. It is wise to chat with your doctor before you spend any money on a supplement or take anything new — even an herbal tea blend or a seemingly harmless vitamin.

Consider gathering trustworthy information about the dietary supplement or natural product you want to try and bring this information to your oncologist. New research about supplement use during cancer treatment and recovery is becoming available, and sharing this information with your doctor will help them give you the best advice possible.

Also, be sure to tell your doctor if you took any supplements before your diagnosis.

Once you are done with cancer treatment and into recovery, your oncologist may give you approval to take certain supplements. It is smart to check with your doctor because they will know how long it may take for your body to process cancer treatment, such as chemotherapy, to avoid a potential interaction.

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Joining the team in February 2008 as a writer and editor, Michelle Whitmer has translated medical jargon into patient-friendly information at for more than eight years. Michelle is a registered yoga teacher, a member of the Academy of Integrative Health & Medicine, and was quoted by The New York Times on the risks of asbestos exposure.

Walter Pacheco, Managing Editor at
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10 Cited Article Sources

  1. U.S. Food and Drug Administration. (2017, November 8). What is a dietary supplement?
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  2. Doheny, K. (2008, October 1). Vitamin C and chemotherapy: Bad combo?
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  3. Claghorn, K. (2002, September 29). Is grapefruit contraindicated during chemotherapy?
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  4. Cancer Active. (n.d.). Beware of grapefruit with chemo drugs.
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  5. National Cancer Institute. (2017, April 20). High-dose vitamin C.
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  6. National Institutes of Health. (2011, June 17). Dietary supplements: What you need to know.
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  7. American Cancer Society. (2015, March 31). Dietary supplements: What is safe?
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  8. National Cancer Institute. (2009, August 11). Dietary supplements and cancer treatment: A risky mixture.
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  9. Cancer Research UK. (2014, October 24). The safety of vitamins and diet supplements.
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  10. Petruzzello, M. (n.d.). 7 of the world’s deadliest plants. Retrieved from:

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Last Modified April 10, 2019

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