Dr. Michelle Weiner
Lifestyle Medicine


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Dietary Supplements During Cancer Treatment: Yes or No? Some pills might interfere with chemo – while others may help defend against tumors.

IS IT A GOOD IDEA TO take dietary supplements while going through active cancer treatment? It's a gray area. Some doctors say patients should hold off, at least while undergoing chemotherapy. But some practitioners in complementary or integrative medicine support the use of certain dietary supplements – such as vitamin D, mushroom extracts, green tea and curcumin – in certain cases, saying they may have cancer-fighting properties and reduce treatment side effects.

Research is still evolving, but several points are clear: If used at all, supplements should be taken along with – not substitute for – standard cancer treatment. Also, it's safer when patients tell their doctors about supplements they use. In return, doctors build more trust when they communicate about dietary supplements with an open, informed, patient-centered approach.

Estimates vary, but studies suggest up to 87 percent of women treated for breast cancer take dietary supplements. In general, the bottom line is that many cancer patients use supplements – doctor-recommended or not.

Abundance of Caution

Patients being treated for cancer often take supplements without telling their oncologists, says Dr. Victor Sierpina, a professor of family and integrative medicine at the University of Texas Medical Branch in Galveston, Texas. Oftentimes, the question simply doesn't get asked. But when patients bring it up, he says, "The majority of oncologists are fairly strict in saying, 'You really shouldn't take supplements during active therapy.'" However, Sierpina notes, many patients do extensive reading about supplements online and may know more than their oncologists about supplements, which don't get much attention during medical training.

There are good reasons behind doctors' reluctance, Sierpina says. "The big fear is that supplements will interfere with chemotherapy – either decrease the effectiveness of the drugs, or cause side effects or affect the metabolism of the drugs." 

Sierpina relates how in the early days of the AIDS epidemic, patients tried the supplement St. John's wort to cope with depression. But that backfired – the supplement caused the liver to quickly break down HIV drugs, lowering drug levels in the blood and leading to treatment failure. "So that's one of those horror stories that people don't want to repeat with cancer," he says. Even now, St. John's wort is not recommended for patients undergoing cancer treatment.

Common Supplements

Last September, in the journal Current Oncology Reports, Sierpina listed common dietary supplements and their pros and cons for cancer patients, including the following:

  • Curcumin. Contained in the spice turmeric, which gives Indian food its bright yellow color and distinctive flavor, curcumin has been shown to have cancer-inhibiting action. But caution is advised for patients with gallbladder disease, because it may worsen symptoms by stimulating gallbladder contractions.

  • Glutamine. Because of its helpful effects on the gastrointestinal tract, glutamine may help relieve chemotherapy side effects such as mouth sores and diarrhea. It also might reduce nerve pain from certain drugs. However, glutamine may interact with medication used to prevent seizures.

  • Maitake mushrooms. Traditionally used in Eastern medicine to treat high blood pressure and diabetes, evidence suggests mushroom extracts may have tumor-fighting properties. But extracts are discouraged for patients on medications to lower blood sugar or those who take the blood-thinning drug warfarin, because of increased risk of bleeding.

  • Fish oil. By reducing inflammation, fish oil may potentially slow cancer progression. But patients currently on chemotherapy might do better going off fish oil. A study in the June issue of JAMA Oncology suggests fish oil may reduce chemo's effectiveness, possibly by increasing resistance within cancer cells.

  • Probiotics. During cancer care, probiotics can help treat diarrhea and other GI side effects.

  • Milk thistle. The active part of milk thistle seed, silymarin, may protect the liver from toxic effects of chemotherapy.

Some experts advise against taking antioxidant supplements – such as vitamins A, C and E, and beta-carotene – especially in high doses, during cancer treatment. Evidence is mixed on whether antioxidants increase or reduce cancer risk, according to the National Institutes of Health. A few small randomized controlled studies found people who used antioxidants during cancer treatment fared worse, particularly if they were smokers.

Open Discussion

"There's literally one reason why anyone would ever choose to take [dietary supplements]," says Suzanne Dixon, a registered dietitian and former chair of the Oncology Nutrition Dietetic Practice Group of the Academy of Nutrition and Dietetics. "It's because they think it's going to help. So you can't argue that hope away just by saying, 'Don't take it.'"

Instead, Dixon says, by having an open, nonjudgmental conversation, health professionals can give patients concrete information to help them decide what they should do. An honest assessment of possible harms and benefits lets patients know doctors take patients' interest in supplements seriously, not dismissively. Being clear on which supplements patients are using puts everyone on the health care team on the same page.

Dixon strongly advises patients to seek out a dietitian who's well-versed in cancer treatment, to sort out issues of supplement safety, dosage and timing. "Some nutrients can help people heal better after surgery, for example," she says. "This includes zinc, vitamin C, arginine and glutamine." Brand-name products offer different combinations of these nutrients, she explains, and a dietitian can guide patients through their choices.

Vitamin D is a special case. "All cancer patients should have their vitamin D levels tested," Dixon says, and if levels are low, they should work with their doctor or dietitian on a supplementation plan to return them to a normal range during treatment. Evidence suggests people with vitamin D deficiency don't do as well in terms of cancer survival and symptoms, Dixon says. On the other hand, she continues, if a person is not deficient, "supplementing additional vitamin D is unlikely to offer benefit – and in some cases, may increase risk of complications or cause other harmful health effects."

Sierpina says vitamin D can be taken safely during cancer therapy, with dosing guided by blood levels. "Some cancers can cause a very low level of vitamin D, which can affect immunity and response to therapy," he says. He adds that vitamin D levels above 50 nanograms per milliliter – in the high-normal range – have been shown to reduce the risk of recurrence of breast cancer in survivors.

Food Is Fine

You can't go wrong taking in nutrients naturally – by eating. "Most of us who practice integrative and complementary medicine would prefer that patients take the food from the source, rather than a pill," Sierpina says.

Soy is one example. Soy is a plant-based source of the chemical estrogen. When it comes to hormone-based cancers, like breast cancer, soy supplements are controversial. "So people say, 'Yes, you can eat soy foods – edamame or soy beans or tofu,'" Sierpina says. "But you shouldn't necessarily take high doses of isoflavones, which is an active form of soy in a capsule that you can buy a health-food store."

Research continues, Sierpina says: "In the meantime, people are following the precautionary principle to first do no harm. We have to know it's safe. And if not, presume it's not safe."

Supplements: Not a Standalone

Sierpina has seen a handful of cases where people have declined standard treatment altogether – rejecting radiation, surgery and drugs. He "absolutely" advises against using alternative methods to replace standard treatment. When patients shun standard medical therapy, he says, "The cancer tends to run its course." 

As people transition from cancer patients to cancer survivors, Sierpina says, there's more freedom to use complementary therapies like supplements to improve quality of life. "For reasons of their own, people may feel that taking supplements gives them some autonomy," he says. "Some involvement in their treatment process, some control.

Lisa Esposito, Staff Writer

Lisa Esposito is a Patient Advice reporter at U.S. News. She covers health conditions, drawing ...  READ MORE

Tags: health, patients, patient advice, cancer, breast cancer, chemotherapy, diet and nutrition, supplements, alternative medicine, vitamins, vitamin D

Michelle Weiner