Many of us take vitamin C to ward off a cold, but research is finding that in large doses, the antioxidant might also be a cancer killer. A number of studies have found that large infusions of vitamin C can kill or block the growth of cancer cells while sparing healthy cells, according to a commentary published in the August 12 issue of Proceedings of the National Academy of Sciences (PNAS).
Back in 1973, American scientist Linus Pauling and Scottish doctor Ewan Cameron investigated the use of vitamin C in cancer patients. They theorized that vitamin C inhibits tumor growth, in part by triggering an immune response. Their research was intriguing enough that the National Cancer Institute (NCI) launched two subsequent studies on the subject at the Mayo Clinic. However, when those studies failed to show that vitamin C increased survival in terminal cancer patients, interest in the antioxidant as an anticancer therapy began to wane. (Please see further history of Vitamin C in the November 2006 edition of CancerWire available here.)
Where the NCI studies were likely missing the mark was by giving vitamin C orally in relatively small doses, say the commentary authors, Balz Frei, PhD, director and endowed chair, and Stephen Lawson, both of the Linus Pauling Institute at Oregon State University. “We know that IV vitamin C produces levels in blood that are many times greater than those achieved with oral supplementation, and these very high concentrations may be necessary to kill cancer cells,” says Lawson.
This idea that large IV doses of vitamin C destroy cancer cells while leaving healthy cells intact is the basis of more recent studies by Mark Levine, MD, chief of the Molecular and Clinical Nutrition Section at the National Institute of Diabetes and Digestive and Kidney Diseases. High concentrations of vitamin C can act as a pro-oxidant in the body, producing hydrogen peroxide (H2O2), which damages cancer cells and ultimately leads to their demise. Meanwhile, normal cells survive because they aren’t as vulnerable to the effects of hydrogen peroxide. In a study published in the same issue of PNAS, Dr. Levine’s group found that injecting vitamin C directly into the bodies of mice inhibited tumor growth by about 50 percent.
The potential for vitamin C to destroy cancerous cells is substantial, and the regimen appears to be well tolerated, but there is still a “missing link,” Dr. Frei says. For vitamin C to act as a pro-oxidant and produce hydrogen peroxide, a protein that contains “redox-active” metal ions such as copper or iron must be present. Researchers still don’t know exactly what that metal-containing protein is, but they believe it will be the key to any anticancer effect of vitamin C.
“Hopefully, Levine’s work will spark renewed interest into the cancer therapeutic potential of vitamin C,” Frei says. “What is needed now are randomized, placebo-controlled, double-blind clinical trials of IV vitamin C in cancer patients.” Future research will help determine the optimum dose and delivery method, and enable scientists to learn exactly how vitamin C creates the hydrogen peroxide that destroys cancerous cells.
Note: Vitamin C is not FDA approved to prevent, treat or mitigate cancer. If you are interested in taking vitamin C please consult with your licensed healthcare practitioner.
Frei B, Lawson S. Vitamin C and cancer revisited. PNAS. 2008;105:11037-11038.
Chen Q, Espey MG, Sun AY, Pooput C, Kirk KL, Krishna MC, Khosh DB, Drisko J, Levine M. Pharmacologic doses of ascorbate act as a prooxidant and decrease growth of aggressive tumor xenografts in mice. PNAS. 2008;105:11105-11109.