VITAMIN C HEALTH CLAIMS FOR REDUCED CANCER RISK MUST BE SUPPORTED BY STUDIES SHOWING VITAMIN IS CAUSE OF BENEFIT AND NECESSARY INTAKE RANGE -- FDA
Health claims that vitamin C reduces the risk of some cancers must be supported by studies showing that the vitamin itself is the cause of the reduced risk and demonstrating the range of vitamin C intake necessary for risk reduction, FDA's proposed rules for food labeling state. Published in the Nov. 27 Federal Register, the agency's 525- page package of proposed rules for food labeling and nutritional guidelines states in the section on "antioxidants, vitamins and cancer" that FDA is requesting studies on: "1) whether vitamin C itself, rather than some other component of food, decreases the risk of cancer in humans and 2) the range of intake in which vitamin C produces this effect." FDA tentatively has decided "not to authorize the use on foods, including conventional foods and dietary supplements, of claims relating to associations between ingestion of vitamin C and reduced risk of cancer" pending receipt of supportive studies. After reviewing 36 scientific studies of a possible link between vitamin C ingestion and a reduction in the occurrence of certain cancers, FDA concluded that "there is not significant scientific agreement, among experts qualified by scientific training and expertise . . . that the claim associating vitamin C to risk of cancer is supported by such evidence." Although the agency found that "the evidence is strong that consumption of fruits and vegetables . . . is associated with lowered risk of cancer," particularly of the stomach, "the data are not sufficiently convincing that vitamin C itself is responsible for this epidemiological association," the proposed rule states. Most of the studies submitted concerning the health benefits of vitamin C were prospective ones based on interviews and/or food frequency questionnaires to determine subjects' intake of vitamin C-rich foods and a broad spectrum of possible cancer risk factors. These surveys, FDA said, "do not clearly demonstrate that the effects are the result of vitamin C per se." "Further," the agency said, "even if the evidence for a cause- and-effect relationship of vitamin C intake with lowered risk of stomach cancer was assumed to be adequate, the agency finds the data to be insufficient to determine the quantity of vitamin C needed to produce the effect." The notice continues: "if such data were available, it would be necessary for the agency to determine whether the food supply already provides enough vitamin C to produce that [cancer-preventing] effect." Three of the 36 studies FDA reviewed would seem to come closest to the agency's ideal for collecting specific data on vitamin C's potential health benefits; however, the agency found shortcomings in all three. Two placebo-controlled trials involved people who either had colon or rectal polyps or had family members with polyps and attempted to determine if there is a link between vitamin intake and polyp development. FDA criticized the studies for mixing vitamin C, vitamin E and fiber as supplements; being too small in size; and having "no biochemical analysis." The third trial, which used both questionnaires and blood samples of ascorbate and pepsinogen levels in an effort to determine why there were differing rates of stomach cancer in two adjacent Welsh towns, was criticized by the agency for a lack of dietary data and information regarding the questionnaire and a failure to match study participants by health history, smoking and demographics. FDA similarly decided to tentatively disallow cancer risk reduction health claims for beta-carotene and vitamin E pending receipt of studies that are agent-specific and explore the amount of a nutrient necessary to achieve the desired effect. In the case of vitamin E, FDA also wants evidence of "factors which may limit any vitamin E effect." An agency review of 22 studies on vitamin E and 26 beta-carotene studies found a lack of "scientific agreement" similar to that for the vitamin C studies. The food labeling/nutritional guideline package contains statements on health claims for calcium, dietary fiber and cancer, dietary fiber and cardiovascular disease, dietary lipids and cardiovascular disease, lipids and cancer, folic acid, omega-3 fatty acids, sodium and zinc. For all the potential health claims evaluated, FDA reviewed a total of 460 individual studies. So far, FDA is allowing health claims for only four categories: sodium and hypertension; calcium and osteoporosis; lipids and cardiovascular disease; and lipids and cancer ("The Pink Sheet" Nov. 11, T&G-4). The proposed regs are subject to a 90-day comment period, and then will be finalized by Nov. 8, 1992 and take effect May 8, 1993.
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