Thursday October 2, 2008 (foodconsumer.org) -- Vitamin C may reduce the effectiveness of some chemotherapy drugs, according to researchers at Memorial Sloan-Kettering Cancer Center.

The researchers published a study in the October 1 issue of Cancer Research saying that a cell culture study and a mouse study suggested that high doses of vitamin C would reduce the patients' ability to respond to therapy.

The actual agent used for the studies is dehydroascorbic acid that the researchers claimed is the form of ascorbic acid or vitamin C that enters cells, meaning that the results may not necessarily apply to vitamin C!

There has been some concern in the medical circle that dietary antioxidants neutralize free radials that some chemotherapy drugs generate to kill cancer cells and reduce the efficacy of the cancer drugs.

This study was meant to determine the effect of vitamin C on the effectiveness of some chemotherapy drugs.

For the study, Mark Heaney and colleagues first tested drugs in a cancer cell culture treated with dehydroascorbic acid and found drugs only killed 30 to 70 percent less cancer cells when treated with the compound.

They also implanted cancer cells treated with or without dehydroascorbic acid into mice and found that tumors grew more rapidly in mice that received cancer cells treated with the compound.

Heaney and colleagues said the counteracting effect of this compound was not due to the antioxidant's neutralizing of free radicals by which some anticancer drugs kill cancer cells.   Rather it is because dehydroascorbic acid prevented cancer cells damaged by chemotherapy drugs from dying by reviving damaged mitochondria in the cells.

The researchers said that the level of dehydroascorbic acid used in the study was similar to the level found in cancer patients who used mega-doses of vitamin C.

A health observer who did not want to be named suggested that the study results may not apply to cancer patients not only because this is an animal study, but also because according to some doctors vitamin C is so regulated that the amount allowed to get into cells is limited.

Early studies of low doses of vitamin C disproved a theory that vitamin C orally administered helps prevent or treat cancer because the amount of the vitamin in the blood is not high enough to kill cancer cells.  

On the other hand, some studies also found high levels of vitamin C in the blood which can be achieved by IV-injection killed cancer cells rapidly while posing no risk to the healthy cells.   One study was conducted by researchers at the National Cancer Institute.

IV-injection of vitamin C has been used by some alternative practitioners for years if not decades to treat a variety of cancer although efficacy if such therapies largely remain unreported.

With regard to the effect of vitamin C on chemotherapy, not all studies came in agreement with the Heaney’s study.

A review of 19 trials  found no evidence to suggest that antioxidant supplements interfere with the therapeutic effects of chemotherapy agents.   As a matter of fact, these supplementary therapies may help increase survival rates, tumor response, and the patient's ability to tolerate treatment, the study found.

The review was published in the May, 2007 issue of the peer-reviewed journal Cancer Treatment Reviews.

"This review demonstrates that there is no scientific support for the blanket objection to using antioxidants during chemotherapy. In addition, it also appears that these supplements may help mitigate the side effects of chemotherapy," said Keith I. Block, MD, lead author of the study and Medical Director of the Block Center for Integrative Cancer Treatment.

"This is significant because it increases the likelihood that patients will be able to complete their treatment," Said Block.

The 19 trials were selected from 845 studies from five scientific databases and the researchers believed they were most trustworthy and reliable. The antioxidants evaluated included glutathione, vitamin A, vitamin C, vitamin E, ellagic acid, selenium and beta carotene.

The researchers found patients who received antioxidants had similar or better survival and no studies supported the theory that antioxidant supplements diminish the efficacy of chemotherapy treatments.

All but one of the studies showed patients receiving antioxidants had better or similar response than the control group and 15 out of 17 trials showed patients on antioxidants suffered similar or lower rates of side effects than the control group.

Co-author Dr. Robert Newman, Professor of Cancer Medicine at M. D. Anderson Cancer Center said, "This study, along with the evolving understanding of antioxidant-chemotherapy interactions, suggests that the previously held beliefs about interference do not pertain to clinical treatment."

The issue on vitamin and cancer is highly controversial.   Last famous chemist Dr. Linus Pauling said that his research showed patients who received conventional treatments plus vitamin C supplement lived much longer than those who used only conventional treatments such as chemotherapy.

As the researchers of the current study acknowledged that some studies found that vitamin C and other antioxidant vitamins do not interfere with cancer therapy.