Injecting high doses of vitamin C into mice with aggressive cancers slowed the growth of their tumors significantly without affecting normal tissues, researchers are reporting. While the potential anticancer effects of vitamin C (also known as ascorbate or ascorbic acid) have been studied for decades, the new findings provide "a firm basis" for advancing vitamin C as a pharmacologic agent for treating human cancer, they write in the August 5 Proceedings of the National Academy of Sciences.

To test vitamin C injections, Dr. Mark Levine of the National Institute of Diabetes and Digestive and Kidney Diseases and his colleagues delivered high doses of ascorbate into the veins or abdominal cavities of mice with aggressive forms of brain, ovarian, and pancreatic tumors. The injections reduced tumor growth by approximately half compared with xenografts in untreated mice.

The delivery method appears to be critical for efficacy. When vitamin C is taken orally, the body prevents blood levels of ascorbate from exceeding a narrow range. This may explain why two previous NCI-sponsored clinical trials found no survival benefit from vitamin C given orally. Although scientific interest in vitamin C for cancer diminished after the second study appeared in 1985, some complementary and alternative medicine practitioners have continued to administer high doses of ascorbate to cancer patients.

The new findings suggest that hydrogen peroxide formation, a result of the ascorbate treatment, is responsible for the anticancer activity. Thus, the study provides a much-needed biological rationale for testing the strategy in patients, notes an accompanying editorial.

The vitamin C treatments did not cure the mice, so the study authors suggested that high doses of intravenous ascorbate should be studied in combination with other cancer therapies in humans.