The long-dormant debate over vitamin C's usefulness for cancer therapy may be about to reignite. Researchers have found that injecting mice with high doses of the vitamin staved off tumor growth. The findings could upend the established view that vitamin C is useless as a cancer treatment.
The idea that high doses of vitamin C, or ascorbic acid, might help cancer patients first surfaced in the late 1970s. It sparked a heated debate within the research community until studies in 1979 and 1985 by scientists at the Mayo Clinic in Rochester, Minnesota, seemed to demonstrate no benefit. But Mark Levine, a physician and cell biologist at the National Institute of Diabetes and Digestive and Kidney Diseases in Bethesda, Maryland, decided to reinvestigate once he realized that patients in the Mayo study had ingested the vitamin. The intestine absorbs only a limited amount of ascorbic acid, so those patients did not get a full dose, he says.
Levine and his colleagues tested high doses of vitamin C delivered directly to tumors. They grew 43 types of cancer cells and five strains of normal cells on a medium with vitamin C. For 75% of the tumor types, less than 10 millimoles of the vitamin killed about half of the cells while sparing normal cells. Next, the researchers implanted mice with pancreatic, breast, and brain cancer cells. They injected half of the rodents with enough vitamin C so that the concentration in the fluid around their cells would reach at least 10 millimoles. Tumors in the mice that received the shots grew by 41% to 50% less than growths in mice that did not receive the treatment.
In humans, the concentration of ascorbic acid in the extracellular fluid normally doesn't climb higher than 0.2 millimoles. But in other studies, researchers have injected humans with the same solution they gave the mice and increased vitamin C in the blood to more than 10 millimoles. Those recipients showed few adverse effects, the team notes.
The results show that high doses of injected vitamin C could be another weapon against cancer, the researchers conclude in this week's issue of the Proceedings of the National Academy of Sciences. Levine speculates that a massive dose of ascorbic acid triggers a chemical reaction that produces high levels of hydrogen peroxide. Normal cells have enzymes and other mechanisms that prevent hydrogen peroxide from damaging them. But some cancer cells seem to lack those controls and die when concentrations of hydrogen peroxide are too high. Levine says potential to help treat cancer with minimal side effects makes vitamin C worth pursuing, in spite of the historical controversy surrounding the treatment.
Other researchers are encouraged by the results. Chi Dang, a cancer biologist who has performed similar work with vitamin C at Johns Hopkins University in Baltimore, Maryland, says the data are sound and deserve further exploration. "I hope people will look at this more objectively without the baggage from history," he says. But Stephen Barrett, who runs the anti-fraud Web site Quackwatch and has long opposed the use of high doses of vitamin C, remains skeptical that this will lead to practical applications in humans: "I hope this will not touch off a rash of people to offbeat practitioners to get intravenous vitamin C."