 August 2008 Parenteral treatment with vitamin C can reduce the growth of aggressive tumor xenografts in mice, according to a report in the August 4th Early Edition of the Proceedings of the National Academy of Sciences. Although vitamin C is typically thought of as an antioxidant, Dr. Mark Levine and colleagues show in the new study that it can also act as a prooxidant. The results also indicate that at pharmacologic levels, the essential nutrient elicits hydrogen peroxide-dependent cytotoxicity only toward cancer cells, leaving normal cells unscathed. Testing in mice with glioblastoma xenografts showed that a single parenteral dose of vitamin C leads to free radical formation in tumor interstitial fluids, but not in the blood, Dr. Levine, from National Institutes of Health in Bethesda, Maryland, and co-authors found. Daily treatment with vitamin C significantly slowed the growth of glioblastoma, ovarian cancer, and pancreatic cancer in mice. To gauge the therapeutic potential of vitamin C, the researchers administered the nutrient intravenously to humans and found that concentrations corresponding to the efficacious levels in mice were, in fact, achievable. Despite these encouraging results, the authors note that "use of pharmacologic ascorbate as a single agent was not curative." Still, they believe that it could be used in combination with other therapies to increase the efficacy against prognostically poor malignancies, such as those examined in the study. Reuters Health, August 2008 U. S. Department of Health and Human Services U. S. Food and Drug Administration Center for Food Safety and Applied Nutrition Office of Nutritional Products, Labeling and Dietary Supplements April 1, 2003 Letter Regarding Dietary Supplement Health Claim for Antioxidant Vitamins and Risk of Certain Cancers Jonathan W. Emord Emord and Associates, P.C. Suite 600 1050 17th Street, N.W. Washington, D.C. 20036 Dear Mr. Emord: This letter is a follow-up to the Food and Drug Administration's February 11, 2003, letter, pursuant to the opinion and order issued December 26, 2002, by the U.S. District for the District of Columbia in Whitaker, et al. v. Thompson, et al., Civil No. 01-1539, and your response dated February 13, 2003. As you know, the United States withdrew its notice of appeal in this matter on March 28. The purpose of this letter is to formalize the contingent understanding we reached in mid-February. In its opinion and order, the Court instructed FDA to draft one or more "short, succinct, and accurate disclaimers" for the health claim: "Consumption of antioxidant vitamins may reduce the risk of certain kinds of cancer." Slip Op. at 37; see Order at 1-2. As we explained in our February 11 letter, FDA considered the two disclaimers suggested by the Court, as well as a number of others, and concluded the following three alternative disclaimers best meet the criteria specified in the Court's decision: Some scientific evidence suggests that consumption of antioxidant vitamins may reduce the risk of certain forms of cancer. However, FDA has determined that this evidence is limited and not conclusive. Some scientific evidence suggests that consumption of antioxidant vitamins may reduce the risk of certain forms of cancer. However, FDA does not endorse this claim because this evidence is limited and not conclusive. FDA has determined that although some scientific evidence suggests that consumption of antioxidant vitamins may reduce the risk of certain forms of cancer, this evidence is limited and not conclusive. Your February 13 letter indicated that your clients accept these disclaimers, and that the various petitioners in this matter wish to have the option of using any of three disclaimers on their products with the antioxidant vitamin claim. FDA intends to exercise its enforcement discretion with respect to antioxidant vitamin dietary supplements containing vitamin E and/or vitamin C when: (1) one of the above disclaimers is placed immediately adjacent to and directly beneath the antioxidant vitamin claim, with no intervening material, in the same size, typeface, and contrast as the claim itself; (2) the supplement does not recommend or suggest in its labeling, or under ordinary conditions of use, a daily intake exceeding the Tolerable Upper Intake Level established by the Institute of Medicine (IOM) of 2000 mg per day for vitamin C and 1000 mg per day for vitamin E (see May 4, 2001, letter at 4-6 and references cited therein). Antioxidant vitamin supplements bearing the claim and one of the disclaimers are still required to meet all applicable statutory and regulatory requirements under the Federal Food, Drug, and Cosmetic Act, including the applicable requirements for health claims. Sincerely, Christine L. Taylor, Ph.D. Director Office of Nutritional Products, Labeling and Dietary Supplements Center for Food Safety and Applied Nutrition - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Antioxidants in Cancer Therapy; Their Actions and Interactions With Oncologic Therapies Davis W. Lamson, MS, ND and Matthew S. Brignall, ND Abstract There is a concern that antioxidants might reduce oxidizing free radicals created by radiotherapy and some forms of chemotherapy, and thereby decrease the effectiveness of the therapy. The question has arisen whether concurrent administration of oral antioxidants is contraindicated during cancer therapeutics. Evidence reviewed here demonstrates exogenous antioxidants alone produce beneficial effects in various cancers, and except for a few specific cases, animal and human studies demonstrate no reduction of efficacy of chemotherapy or radiation when given with antioxidants. In fact, considerable data exists showing increased effectiveness of many cancer therapeutic agents, as well as a decrease in adverse effects, when given concurrently with antioxidants. Alternative Medicine Reviews, 1999;4(5):304-329 |
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