Vitamin C may treat cancer after all.

Despite Nobel laureate Linus Pauling's advocacy of vitamin C as a way for people to battle cancer, research has rarely found that doses of the nutrient affect the course of the disease. However, a new investigation shows that vitamin C could be an effective cancer fighter after all, but only when taken intravenously.

Mark Levine of the National Institute of Diabetes and Digestive and Kidney Diseases in Bethesda, Md., and his colleagues had previously found that people quickly clear vitamin C from their bodies when it's taken orally, so their blood concentrations stay low. When the nutrient was delivered intravenously, however, volunteers' blood concentrations of the vitamin were up to 70 times as high as they were with oral dosing. These high blood concentrations didn't appear to have any harmful effects on the study participants.

Experiments that previously had discounted vitamin C's cancer-fighting effects had mainly involved oral doses, says Levine. To test how higher concentrations might affect cancer, his team applied vitamin C at concentrations that mimic intravenous ones to healthy human and mouse cells in lab dishes and various types of cultured cancer cells.

After incubating the cells with vitamin C for 1 hour, Levine and his colleagues found that the nutrient killed go percent of cancer cells in 5 of 10 cancer-cell cultures but had no effect on healthy cells. Further tests found that a chemical reaction on the outside of cancer cells converted vitamin C into hydrogen peroxide, a potent free radical that kills cells.

Levine says that these results, published in the Sept. 20 Proceedings of the National Academy of Sciences, may prompt researchers to reconsider intravenous vitamin C as a treatment for cancer and other diseases. --C.B.