Washington: Vitamin C, in pre-clinical studies, was found to erode the effectiveness of anti-cancer drugs, according to a new study.

These new findings came from a study of lab cancer cells and mice, but the authors of the study said 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 Mark Heaney, an associate attending physician at Memorial Sloan-Kettering Cancer Centre (MSKCC).

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.

Heaney and his colleagues 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 pre-treated with vitamin C, as they did on untreated cancer cells.

The team, which includes researchers from Columbia University, then delved into the mechanism by which vitamin C may be protecting these cells.

They found instead that DHA was restoring viability to the cancer cell's damaged mitochondria - the cell's all-important power plant that, when injured, sends signals to force a cell to die, according to a release of American Association for Cancer Research.

Heaney said that he suspects that vitamin C is good for the cells of normal tissue because it... probably extends cell life. "But that isn't what you want when you are trying to eliminate cancer cells."

These findings were published in the Wednesday issue of Cancer Research. IANS