Researchers at the University of Pennsylvania Center for Cancer Pharmacology in Philadelphia and the news media overlooked five separate human studies that disproved high-dose vitamin C causes DNA damage and instead chose to make headlines out of a singular test-tube study that concluded that a 200 mg dose of vitamin C could potentially cause cancer.
While millions of Americans who take vitamin C supplements were beginning to question whether high-dose vitamin C is safe, Ian A. Blair, the lead researcher in the study published in the June 15 issue of Science, was unavailable for comment. Usually test-tube studies precede animal or human studies, and results in the laboratory often do not coincide with those found in living systems. In this case, human studies had already been performed and have, as expected, not confirmed the notion that vitamin C is toxic to living cells or DNA.
Although researchers are puzzled as to why vitamin C supplements do not always reduce the risk for cancer, there are no studies that confirm that vitamin C users are at greater risk for cancer.
The report in Science was submitted in early February, approved for publication in May 2001 and included other published references dated as late as the year 2000. Four of the five human studies that do not confirm that vitamin C causes DNA damage were published in 2000 and could have been cited by the authors of the report in Science, but were overlooked.
For example, researchers at Johns Hopkins University in Baltimore could not find evidence of a "significant main effect or interaction effect on oxidative DNA damage in nonsmoking adults" with 500 mg per day of vitamin C supplementation. [Cancer Epidemiology Biomarkers Prevention 2000 July; 9:647-52]
Another study, conducted by researchers in Germany, found that 1,000 mg of vitamin C consumed by smokers and nonsmokers for seven days did not produce DNA damage as measured by the number of micronuclei in blood lymphocytes. [Free Radical Research, 2001 March; 34:209-19]
In yet another study conducted by Immunosciences Laboratory in Beverly Hills, Calif., 20 healthy volunteers were divided into four groups and given either placebo or daily doses of 500, 1,000 or 5,000 mg of ascorbic acid for a period of two weeks. This study concluded that "ascorbic acid is an antioxidant and that doses up to 5,000 mg neither induce mutagenic lesions nor have negative effects on natural killer cell activity, apoptosis or cell cycle." [Cancer Detection Prevention, 2000; 24:508-23].
In London, researchers measured the effects of 260 mg per day of vitamin C and vitamin C plus iron in humans and concluded that there was "no compelling evidence for a pro-oxidant effect of ascorbate supplementation, in the presence or absence of iron, on DNA base damage." [Biochemistry Biophysical Research Communications, 2000 Nov. 2; 277:535-40]
In Ireland, researchers gave 1000 mg of vitamin C to volunteers for 42 days and concluded that "supplementation with vitamin C decreased significantly hydrogen-peroxide-induced DNA damage in peripheral blood lymphocytes." [British Journal Nutrition, 2000 Aug.; 84:195-202]
The media was also remiss in not checking whether there was contrary data and did not interview other scientific sources, such as the Linus Pauling Foundation, the Vitamin C Foundation, the NNFA or the CRN. Reuters and Associated Press health reporters ran the story without checking the validity of the report in Science. A cub reporter could have uncovered the five contrary human studies in a 30-minute search on Medline.
Recently researchers have been exploring the dual nature of vitamin C. Is vitamin C a pro-oxidant or rusting agent, or is it an antioxidant, a cellular preservative? In 1998, Nature published a report similar to the University of Pennsylvania study. Researchers then claimed that high-dose vitamin C had "rusting" properties in living cells. But the researchers overlooked that high-dose vitamin C also increased the level of guanine, another of the nucleic acids in DNA. The researchers failed to point out their paradoxical results and the media made headlines out of the story then, as they are doing now. No corrections were ever published, so the public was left with the impression that high-dose vitamin C is potentially dangerous.
—Bill Sardi, Knowledge of Health, Inc.
Natural Foods Merchandiser volume XXII/number 8/p. 14