WASHINGTON Vitamin C supplements may undercut the effectiveness of cancer drugs including Novartis' Gleevec, a U.S. study published on Wednesday showed.
When used on human cancer cells treated with a form of vitamin C in lab dishes, chemotherapy drugs killed 30 percent to 70 percent fewer tumor cells than usual, the scientists wrote in the journal Cancer Research.
Dr. Mark Heaney of Memorial Sloan-Kettering Cancer Center in New York and colleagues also implanted human cancer cells into mice, and found that when mice got vitamin C supplements two hours before chemotherapy, the tumors grew more quickly.
They tested five common chemotherapy drugs including Gleevec, also known as imatinib.
"The vitamin C didn't neutralize the effects of the chemotherapy drugs, but it blunted their effects," Heaney said in a telephone interview.
The other drugs were doxorubicin, cisplatin, methotrexate and vincristine. They work in different ways to combat tumors.
"Vitamin C is something everyone needs to have in their diet or you develop scurvy. But I don't recommend taking supplemental vitamin C during that period of time that my patients are receiving chemotherapy," Heaney added.
Heaney said it did not appear that the antioxidant properties of vitamin C were the culprit. Rather, it may be the protective effect vitamin C has on mitochondria -- which generate energy for a cell -- within cancer cells, he added.
Chemotherapy drugs damage mitochondria in cancer cells.
"When mitochondria are damaged, they can send signals to the cell to die. And that's, we think, one of the ways that the chemotherapy drugs exert their beneficial effects. And vitamin C helps to preserve the health of the mitochondria," Heaney said.
By protecting the mitochondria, vitamin C prevents chemotherapy agents from working to their full potential.
Heaney acknowledged that a study looking at cancer cells in laboratory dishes or in mice is not the final word on the subject, and said more research is needed.
The findings are the latest development in the controversy over vitamin C and cancer. The notion that vitamin C, also known as ascorbic acid, could be used to treat cancer was advanced in the 1970s by American scientist Linus Pauling, who was awarded the Nobel Prize in chemistry in 1954.
Studies in which vitamin C pills were given to treat cancer failed to show a benefit.
But a study at the U.S. National Institutes of Health published in August showed that injections of high doses of vitamin C greatly reduced the rate of tumor growth in mice.
(Editing by Maggie Fox and Xavier Briand)