Wednesday, an United States study has revealed that higher doses of vitamin C might reduce the effectiveness of a wide range of anti-cancer drugs including Novartis' Gleevec.

Even though the research focused on laboratory cancer cells and mice only, the findings raise questions about whether human patients might be subject to similar effects. After having undergone pretreatment with vitamin C, thirty to seventy percent less cancer cells in a laboratory were killed by a range of drugs. Chemotherapy tests were performed afterwards, showing that tumours grew more rapidly in mice that had cancer and had been pretreated with vitamin C.

There is no sign, however, that smaller doses of vitamin C, such as the usual ones found in fruits and vegetables or ordinary multivitamins, might also be considered harmful.

Some scientists, including the late Linus Pauling, who was awarded the Nobel Prize in chemistry in 1954, have viewed vitamin C as a potential cancer fighter for a long time, although no one could tell the reason why.

For this study, scientists tested five chemotherapy drugs including doxorubicin, cisplatin, vincristine, methotrexate and imatinib (Gleevec).

"The vitamin C didn't neutralize the effects of the chemotherapy drugs, but it blunted their effects," study author Dr. Mark L. Heaney stated in a telephone interview.

Heaney added that he believed vitamin C was beneficial for cells of normal tissue, because it provided extra protection for the mitochondria, therefore extending the cells’ life.

Scientific adviser and spokeswoman for the Health Supplements Information Service Pamela Mason informed that the study had reached an undeniable conclusion about the reduction of effectiveness in the case of anticancer drugs in mice affected by the disease, leaving the implications for human beings to be further tested.