Vitamin C and Chemotherapy: Bad Combo?

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.