The National Institutes of Health researchers link the effect of vitamin C -- ascorbate or ascorbic acid -- to the formation of hydrogen peroxide in the extracellular fluid surrounding the tumors that killed cancer cells but left normal cells unaffected.

The researchers injected very high doses -- 4 gm per kilogram of body weight daily -- directly into the veins or abdominal cavities of the mice with aggressive brain, ovarian and pancreatic tumors.

"When you eat foods containing more than 200 milligrams of vitamin C a day -- for example, 2 oranges and a serving of broccoli -- your body prevents blood levels of ascorbate from exceeding a narrow range," the study lead author Dr. Mark Levine said in a statement. "At these high injected doses, we hoped to see drug-like activity that might be useful in cancer treatment."

The NIH experiments tested high concentrations of ascorbate on 43 cancers and 5 normal cell lines and found that high concentrations of ascorbate had anti-cancer effects in 75 percent of cancer cell lines tested and spared all the normal cells.

The findings are published in the Proceedings of the National Academy of Sciences.