High Doses of Vitamin C May Interfere With Cancer Treatments

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March 27, 2000 (Tampa, Fla.) -- A new study suggests that taking vitamin C supplements may not be a good idea for cancer patients. In fact, researchers say, the vitamin may protect tumors from the killing effects of radiation and chemotherapy.

The scientists, who presented their findings at a meeting sponsored by the American Cancer Society, stop far short of recommending that everyone avoid vitamin C. If a person is healthy with no evidence of cancer, there should be no worries, says study author David W. Golde, MD.

"Our recommendations are a healthy diet of fruits and vegetables with high intake of [dietary] vitamin C," he says. "I don't argue with anyone who takes vitamin supplementation. On the other hand, in a patient with active cancer being treated with chemotherapy or radiation therapy, we think it's prudent not to take high doses of vitamin C."

Golde, who is physician-in-chief at Memorial Sloan-Kettering Cancer Center in New York, cautions that his team's research, conducted in mice, does not prove that vitamin C is harmful. But, he says, it does suggest that a biological mechanism exists that could mean megadoses of the supplement would be harmful to certain people.

"That's one thing we don't often [know] about: the nutritional needs of the cancer itself ... what it needs to grow, what it seems to want to help its development," says Golde, speaking at the American Cancer Society's Science Writers' Seminar here Monday.

Researchers do know that vitamin C is an antioxidant. It is taken up in large quantities by cells and can protect them from certain kinds of damage, called oxidative damage, that has been linked to heart disease and stroke. But radiation and chemotherapy rely on causing oxidative damage to destroy cancerous cells.

In their research, Golde and colleagues found that cancer cells take in more vitamin C than normal cells. They do this through a system of transporters on their surfaces that pull large amounts of the vitamin into the cell, where it is stored or used to promote the cell's functions, including tumor growth.

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Thus, Golde says, high doses of the vitamin could theoretically protect cancer cells from the very therapy meant to kill them. Although the study was done in mice, Golde says this could be translated to human cancers.

Medical experts at the meeting say that the findings highlight the importance of patients discussing all use of supplements, including vitamins and herbs, with their doctors -- especially if they are undergoing treatment for cancer or other life-threatening diseases.

"Alternative therapies may keep patients from getting the care they need in a timely fashion, " says Barrie Cassileth, PhD, chief of the integrative medicine service, department of medicine, at Memorial Sloan-Kettering Cancer Center.

At this point, Golde says, his study is preliminary. "Prudent advice is: very good nutrition for all people, including cancer patients. But, when it comes to supplementation -- taking very high does of vitamin C -- it's reasonable not to take it during [cancer] therapy," he says.

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