Vitamin C Megadoses Hamper Cancer Treatments in Mice

Oct. 2 -- WEDNESDAY, Oct. 1 (HealthDay News) -- Large doses of vitamin C could reduce the effectiveness of anticancer drugs, according to a new study that focused on laboratory cancer cells and mice.

The finding raises questions about whether human patients might suffer the same effects, the study authors said.

"There's a possibility that taking supplemental vitamin C could have a detrimental effect on cancer treatment," said study author Dr. Mark L. Heaney, associate attending physician at Memorial Sloan-Kettering Cancer Center in New York City.

However, there's no indication that smaller doses of vitamin C, such as those found in food and ordinary multivitamins, might be a problem, he said.

Vitamin C has not traditionally been considered a hindrance to cancer treatment. In fact, some scientists -- including the late Linus Pauling -- have long viewed vitamin C as a potential cancer fighter. Recent research has suggested that vitamin C could help prevent cancer, but it's not clear why.

The vitamin, found in fruits and vegetables, also has a reputation as a treatment or preventive for a variety of ailments, including colds.

In the new study, Heaney and his colleagues gave doses of vitamin C to mice with tumors before they underwent chemotherapy. While the type of vitamin C given to the mice isn't available over the counter, it's the equivalent of a 2,000-milligram dose for humans, Heaney said. That's the equivalent of the vitamin C found in 75 six-ounce glasses of orange juice. Supplements packing that much vitamin C are found in health stores, he said.

The researchers found that the vitamin C reduced the effectiveness of the chemotherapy by about 30 percent to 70 percent.

Heaney theorized that it's possible that vitamin C may disrupt chemotherapy's killing processes and provide protection to the cancer cells.

The findings were published in the October issue of the journal Cancer Research.

Heaney said the next step is to launch studies with people, but, he added, it may be a "hard sell" to convince patients to take high-dose vitamin C supplements if it appears they counteract chemotherapy.