Being Treated for Cancer? Skip the Antioxidant Supplements

The jury's still out on whether antioxidants interfere with treatment, so doctors advise holding off.

Video: Cancer Treatments

The message isn't getting out: Oncologists say there's a chance that antioxidant supplements reduce the effectiveness of chemotherapy and radiation therapy, but patients are still taking them. That's according to a new study, which found that 61 percent of breast cancer patients receiving chemo, radiation, or anti-estrogen drug therapy were taking supplements of antioxidants like vitamins C and E, beta carotene, or selenium.

It's not that doctors have shown conclusively that these antioxidants are bad. But there's some evidence that the supplements may protect the very cancer cells that chemo and radiation are attempting to destroy. It's a controversial issue; other researchers think that antioxidants protect the healthy tissues but don't interfere with—and may even help—chemo and radiation in their assault on cancerous cells.

There simply aren't enough data to settle the question, says Heather Greenlee, assistant professor of epidemiology and medical oncology at Columbia University's Mailman School of Public Health and lead author of the study, which appears in the journal Cancer. Nor do we know what dose might be problematic, if indeed there is some level of antioxidant use that people undergoing treatment shouldn't exceed. Her study found that among those using antioxidants, 69 percent were using doses higher than are found in a Centrum multivitamin.

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Because the major questions about antioxidant use and cancer treatment are unanswered, some doctors, such as Gabriella D'Andrea, an oncologist at Memorial Sloan-Kettering Cancer Center, tell their patients to avoid supplementation entirely unless it is specifically prescribed by a doctor. "That means no Centrum, no Flintstones," she says. Others, like Brian Lawenda, clinical director of radiation oncology at the Naval Medical Center in San Diego, tell patients that a multivitamin isn't likely to hurt them but that they should put aside high-dose supplements until treatment is completed.

This doesn't mean, however, that people undergoing cancer treatment should avoid fruits and vegetables, which naturally contain antioxidants. There's clear evidence that medicine and food can interact—women taking tamoxifen, for example, are advised not to drink too much grapefruit juice—but little evidence on do's and don'ts for specific treatments. "People ask me, 'What should I eat?' And we just don't know," says D'Andrea. For now, a balanced diet is the best recommendation.

[Here are 11 easy ways to load up on healthful omega-3 fats.]

Most important is to tell your doctor what medications and supplements you're taking, even things that seem "natural," like green tea extract. Earlier this year, a study found that a certain plant chemical it contains can interfere with the effects of the anticancer drug Velcade.