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VITAMIN C STATEMENT THAT NUTRIENT "MAY BE A FACTOR" IN REDUCING CANCER RISK

This article was originally published in The Tan Sheet

Executive Summary

VITAMIN C STATEMENT THAT NUTRIENT "MAY BE A FACTOR" IN REDUCING CANCER RISK based on "available scientific evidence" was endorsed by four of six scientists on a Nov. 2 panel considering vitamin C and cancer as part of FDA's Nov. 1-3 conference on antioxidant nutrients. Of the six scientists on the panel, two gave unqualified endorsements, two responded affirmatively but "with some limits," and one abstained. The one panelist opposed to the statement was Victor Herbert, MD, Mt. Sinai Hospital, who has launched a personal campaign against wider use of vitamin C supplements because of his concern that a sizable portion of the U.S. population has a positive iron balance and would be harmed by pro-oxidative effects of vitamin C. Herbert was steadfastly opposed to any question posed to the panel that suggested or encouraged increased vitamin C intake in the general population. Asked whether the panel believed that there was compelling epidemiologic evidence associating vitamin C and reduced cancer risk, the entire panel except for Herbert agreed that the evidence supported an association for some cancers and, at least, for stomach cancer. H. Boeing, PhD, German Institute of Human Nutrition in Potsdam, who gave a presentation on the epidemiologic studies, acknowledged that there is "a lot of evidence on fruit and vegetable intake." The panel also agreed that the association of vitamin C and cancer risk reduction was stronger for certain sites. Nearly all of the panelists cited stomach, esophageal and oral cancers. Jerome DeCosse, PhD, Cornell Medical Center, who gave a presentation on animal and clinical data related to vitamin C, also listed pancreatic, cervical and colorectal cancer. However, the panel was unanimous in agreeing that the clinical trial data were weak in supporting an association of vitamin C with cancer inhibition. In a short presentation, panelist James Enstrom, PhD, suggested that vitamin C deserves more recognition as an etiological factor. In a quick summary of epidemiology studies, he noted that the evidence is "suggestive" of a "moderate" effect but that the data are not statistically significant. In another presentation, panel member Robert Jacob, PhD, USDA, noted that in vitro studies have supplied a "great deal of evidence" demonstrating that vitamin C is a free radical "quencher." While the animal studies on vitamin C provide "good evidence," Jacob observed that there are "inconsistencies" and "a lack of unanimity" in the data. Regarding studies in humans, Jacob said he is "less impressed" given the absence of consistent data and a "real lack of positive results." Comparing the current antioxidant debate to "where we were with cigarette smoking [at] about 1950," DeCosse maintained that "there is sufficient evidence, a sufficient degree of belief, to add or at least ensure that our U.S. population has sufficient amounts" of vitamin C. Asserting that there is "absolute, complete clinical safety" with vitamin C, he indicated that the "modest increment" in use would pose little risk. DeCosse was also one of the few panel members during the conference to unilaterally broach the subject of dietary supplementation. Acknowledging that "safety doesn't mean anything unless there is some evidence of benefit," he also noted that "the degree of belief you have to have [in a chemopreventive agent] relates to the safety of [that] agent." Consequently, he suggested that "if you have a modest degree of belief in an absolutely safe agent, the use of a supplement could be appropriate." In addition, DeCosse questioned the usefulness of approaching the efficacy of antioxidant vitamins by looking for a general benefit against cancer. Noting the importance of vitamin A on squamous epithelium and an association of retinoids and beta carotene on such cancer sites, DeCosse maintained that "it is a mistake to look at the effect of an agent on all sites of cancer risk because you are going to dilute or obscure those sites where the agents might be effective." The panel received two questions from the audience directly relating to supplements. Asked if there might be a reason for vitamin C supplementation due to a possible nutrient/drug interaction, Jacob said he was not aware of any data but that it might be a concern if an individual has a low intake of fruit and vegetables. In response to a question about vitamin C supplementation in children, the panel was nearly unanimous in advising against giving supplements to pre-adolescents. During her presentation, panelist Gladys Block, PhD, University of Califomia-Berkeley, pointed to two model health claims already approved by FDA for fat/cancer and calcium/osteoporosis and suggested that FDA has the flexibility to come up with a similar label claim for antioxidant vitamins given the "uncertainties" and absence of data supporting some of the already approved claims. Block even proposed an antioxidant claim: "a diet rich in antioxidants may help reduce the risk of some cancers." Block asserted that the "strength and nature of the evidence" supporting the effectiveness of antioxidant vitamins "is not just epidemiologic - we have in vitro data and animal data which tell us there is something real about antioxidants." In addition, "the epidemiologic data tell us that there is something going on [and] not only is it real but there is an effect in the human population," she contended. Regarding "inconsistencies" in the data, Block suggested that one of the major flaws in the human studies that have been conducted is that vitamin E and "particularly" vitamin C intake from fortified foods and vitamin supplements has been rarely surveyed or analyzed in studies. "The result of this," she said, "is a vastly weakened capability to detect effectiveness."
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