Vitamin C Weakens Chemotherapy Drugs?

Supplementing With Vitamin C May Reduce Effectiveness of Chemotherapy Drugs, Study Shows

By Kathleen Doheny
WebMD Health News

Reviewed By Louise Chang, MD

Oct. 1, 2008 -- Vitamin C supplements and chemotherapy aren't a good combination, says a team of New York researchers. Vitamin C reduced the effectiveness of many cancer drugs, they found in laboratory and animal studies.

"What we found is that vitamin C blunted the effectiveness of all the chemotherapy drugs we studied," says Mark Heaney, MD, PhD, associate attending physician at Memorial Sloan-Kettering Cancer Center in New York and the study's lead author. "What vitamin C does is protect the cancer cells from the chemotherapy mainly by protecting their mitochondria [the cell's power sources]," he tells WebMD.

In the laboratory studies, he says, the vitamin C blunted the effectiveness of the chemotherapy drugs from 30% to 70%, depending on the dose of vitamin C and the chemo drug.

Vitamin C, Chemotherapy Debate

The question of whether vitamin C supplements help or harm cancer patients has been ongoing for more than a decade, Heaney says. Because vitamin C is an antioxidant, some researchers say it could help cancer patients by promoting general health and keeping cells healthy.

But some chemotherapy drugs produce "oxygen free radicals." The oxygen free radicals produced by the chemo drugs are meant to kill the cancer cells.

Under this theory, the vitamin C could soak up these free radicals instead and allow the cancer cells to survive.

Vitamin C, Chemotherapy Study Details

Concerned that vitamin C supplements might do more harm than good, Heaney's team pretreated some cell lines of leukemia and lymphoma with dehydroascorbic acid, the form that vitamin C takes to enter cells, but did not treat other cell lines in the lab.

Then they treated the cell lines with a variety of chemo drugs, including Adriamycin, Platinol, Oncovin, methotrexate, and Gleevec. They measured the effects of pretreating with vitamin C or not pretreating on the cells and the effectiveness of the chemotherapy.

"It didn't neutralize the effect, but it blunted it." Heaney says, with the effect ranging from a 30% to 70% reduction in effectiveness.

Next, they implanted the cancer cells into mice and found that those tumors pretreated with vitamin C grew more rapidly than those lacking vitamin C.

The study findings appear in the journal Cancer Research.

Vitamin C, Chemotherapy: Another Opinion

Applying the findings to people "is impossible," says Balz Frei, PhD, director and endowed chair at the Linus Pauling Institute at Oregon State University in Corvallis, who reviewed the study for WebMD.

He took issue with several aspects of the study. "The dose was very large," he says. But Heaney says the concentrations inside the cells were similar to what you would see in people who took vitamin C supplements.

The researchers only used two types of cancer cells, leukemia and lymphoma, he says. So the results may not apply to other cancers.

Other research has found beneficial effects of vitamin C supplements during cancer chemotherapy, especially in increasing survival times and decreasing side effects, Frei tells WebMD. But he concedes that "vitamin C could be contraindicated during some types of [chemo] drug therapy" and that larger clinical studies are needed to see if vitamin C and chemotherapy are a good combination.

Patients should be monitored by their physician if they do take vitamin C during chemo, he says.

Vitamin C, Chemotherapy: Researchers' Advice for Patients

"I think that patients should probably refrain from taking supplemental vitamin C during chemotherapy," Heaney says.

"If you take an oral dose even as low as 100 milligrams a day you can get concentrations of vitamin C inside your white blood cells that are close to the concentrations that we used experimentally, and that could be harmful," he says.

The recommended intake of vitamin C for healthy people is 75 milligrams daily for women and 90 milligrams daily for men.

Although a multivitamin with vitamin C "would probably be OK,'' taking larger amounts should be avoided while on chemo, Heaney says.

SOURCES: Mark Heaney, MD, PhD, associate attending physician, Memorial Sloan-Kettering Cancer Center; assistant professor of medicine, Weill Medical College of Cornell University, New York. Heaney, M. Cancer Research, Oct. 1, 2008: vol 68: pp 8031-8038. Balz Frei, PhD, director and endowed chair, Linus Pauling Institute, Oregon State University, Corvallis.

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