WASHINGTON (AFP) - High doses of vitamin C injections reduced the size of tumours and slowed cancerous growths by about 50 per cent in laboratory mice, according to US research released Monday. Researchers at the National Institutes of Health noted the phenomenon in brain, ovarian and pancreatic cancers, according to findings published in the August 5 issue of the Proceedings of the National Academy of Sciences. "Researchers discovered that high concentrations of ascorbate had anti-cancer effects in 75pc of cancer cell lines tested, while sparing normal cells," the report said. "The researchers traced ascorbate's anti-cancer effect to the formation of hydrogen peroxide in the extracellular fluid surrounding the tumours. Normal cells were unaffected," it said. Injections were necessary because the body regulates vitamin C when ingested, so that higher doses cannot be attained. "When you eat foods containing more than 200 milligrams of vitamin C a day - for example, two oranges and a serving of broccoli - your body prevents blood levels of ascorbate from exceeding a narrow range," said Mark Levine, the study's lead author and chief of the Molecular and Clinical Nutrition Section of the National Institute of Diabetes and Digestive and Kidney Diseases. Scientists "injected ascorbate into the veins or abdominal cavities of rodents with aggressive brain, ovarian, and pancreatic tumours," the report said, delivering "up to four grams per kilogram of body weight daily." By injecting mice with 43 cancer and five normal cell lines, "the researchers discovered that high concentrations of ascorbate had anticancer effects in 75pc of cancer cell lines tested, while sparing normal cells." Scientists involved with the study also pointed to evidence that "these high ascorbate concentrations could be achieved in people." "In immune-deficient mice with rapidly spreading ovarian, pancreatic, and glioblastoma (brain) tumours ... the ascorbate injections reduced tumour growth and weight by 41 to 53pc." The researchers concluded that the findings "provide the first firm basis for advancing pharmacologic ascorbate in cancer treatment in humans." Vitamin C was considered as a possible treatment for cancer three decades ago, but subsequent studies showed oral doses provided no benefit.