According to researchers at the prestigious Memorial Sloan-Kettering Cancer Centre in Philadelphia, USA, vitamin C supplements may interfere with the action of cancer drugs. The study was revealed Wednesday and published in the journal Cancer Research.

Many patients take vitamin C supplements to aid their immune system during their struggle with the disease. The US team tested the impact of a form of vitamin C on the effectiveness of a range of anti-cancer drugs in tests on mice’s cancer cells in the laboratory. Each and every chemotherapy drug they tested did not work as efficiently if the cancer cells had been pretreated with vitamin C. Patients who were treated with vitamin C had 30% to 70% fewer of their cancer cells killed in treatment, compared to those who did not take the vitamin.

The researchers evaluated such dissimilar cancer agents as doxorubicin, cisplatin, vincristine, methotrexate, and imatinib (Gleevec). They found that pretreatment with vitamin C also caused significant attenuation of doxorubicin activity in mice with lymphoma cell-derived tumors.

"It is notable that the concentration of vitamin C measured in the tumors of the mice in this study was similar to the concentration of vitamin C that can be achieved in human leukocytes with oral vitamin C supplementation, suggesting that our study conditions were relevant to clinical conditions," the authors said.

Chemotherapy drugs damage mitochondria in cancer cells and by protecting the mitochondria, vitamin C prevents chemotherapy agents from working to their full potential.

However, there's no indication that smaller doses of vitamin C, such as those found in food and ordinary multivitamins, might be a problem, said study author Dr. Mark L. Heaney, associate attending physician at Memorial Sloan-Kettering Cancer Center in New York City.