Healthnotes Newswire (June 14, 2001) — Taking high doses of vitamin C may increase the risk of developing cancer, according to an article published today in the journal Science.¹ However, the study was done in test tubes, and the relevance of its findings to humans and other living organisms is far from clear.

According to the report, vitamin C can promote the conversion of a group of chemicals known as lipid hydroperoxides (which are formed in the body during the oxidation of unsaturated fats) into compounds that can damage DNA. This latter class of molecules is believed to be capable of causing cancer. However, the conditions under which these DNA-damaging chemicals were produced bear little resemblance to the chemical environment of living beings. Human blood and cells contain a myriad of antioxidants, enzymes, proteins, and other molecules that interact in extremely complex ways. Because of the intricate nature of biological fluids, it cannot be assumed that chemical reactions that occur in the test tube would necessarily take place in the body.

For example, human tissues contain vitamin E, whereas the buffering solution used in the Science study did not. In humans, vitamin E prevents the conversion of unsaturated fats to lipid hydroperoxides² (the chemicals that were studied in the Science article). This important antioxidant effect of vitamin E is enhanced by the presence of vitamin C.^{3 4} Therefore, it could be reasonably argued that, in real life, vitamin C might actually prevent, not promote, the formation of DNA-damaging chemicals. The bottom line is that one cannot draw any firm conclusions about the risks and benefits of vitamin C from today's article in Science.

Despite sporadic reports suggesting that taking vitamin C supplements could be harmful, the bulk of the scientific evidence suggests that vitamin C might help prevent certain types of cancer. For example, vitamin C inhibits the growth of Helicobacter pylori, a microorganism that grows on the stomach lining of some people and is believed to increase the risk of stomach cancer.⁵ Vitamin C also prevents the conversion of nitrites (which occur naturally in the stomach) into cancer-causing substances called nitrosamines.⁶ In addition, animal studies suggest that extra vitamin C could help prevent bladder^{7 8} and colon cancers.^{9 10}

That today's Science study was deemed worthy of a press release is consistent with reports of an “anti-nutrition” bias in academic medicine. Specifically, many conventional doctors and scientists have resisted the concept that supplementation with vitamins and minerals might have health benefits.¹¹ One of the ways in which this bias has been expressed is in the uncritical acceptance of questionable reports on the dangers of nutrients. Although today's Science article provides some interesting information about the biochemistry of vitamin C, it seems like an unacceptably large leap to infer from this report that vitamin C causes cancer.