Vitamin C May Impact Anti-Cancer Drugs

(October 3, 2008) - That glass of orange juice and that vitamin C (Read about "Vitamins & Minerals") supplement may not be healthy for cancer patients. (Read about "Cancer: What It Is") Researchers say that pre-clinical studies indicate vitamin C appears to substantially reduce the effectiveness of anticancer drugs. (Read about "Cancer Treatments")

The findings are published in Cancer Research, a publication of the American Association of Cancer Research (AACR). They come from studying laboratory cancer cells and mice, but the study's authors say the same mechanism may affect patient outcomes, although they add this premise needs to be tested.

"The use of vitamin C supplements could have the potential to reduce the ability of patients to respond to therapy," said one of the researchers.

Use of vitamin C during cancer treatment has been controversial. Some studies have suggested that because vitamin C is an antioxidant it might be beneficial to cancer patients. But some classes of chemotherapy drugs produce "oxygen free radicals," unpaired oxygen molecules that can fatally react with other molecules in a cell, forcing cell death. In this theory, vitamin C could sop up the radicals, keeping the cancer cell alive despite chemotherapy treatment.

The researchers tested a wide variety of chemotherapy drugs - those that produce reactive oxygen and those that work in other ways - on cancer cells in the laboratory, that were pretreated with dehydroascorbic acid (DHA), the form that ascorbic acid (vitamin C) takes to enter cells.

They found to their surprise that every chemotherapy drug they tested - which included targeted agents like Gleevec - did not work as well if cells were pretreated with vitamin C, as they did on untreated cancer cells. In the cell culture experiments, 30 to 70 percent less cancer cells treated with vitamin C were killed depending on the drug tested.