Carcinogens and Anticarcinogens in the Human Diet A Comparison of Naturally Occurring and Synthetic Substances (1996) / Chapter Skim
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Executive Summary
Executive Summary
Pages 1-18
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reduce various food hazards.
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Ames et al. contend that the per" centage of naturally occurring chemicals testing positive for carci~ nogenicity in rodent bioassays does not slider significantly from the percentage of synthetic chemicals testing positive, and that these proportions are likely to hold for untested agents, leacling to their conclusion that the cancer risk from natural chemicals in the flier might be greater than that from synthetics.
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ies linking the aforementioned mycotoxins to human river cancer provide convincing evidence tint some constituents of foods can cause cancer. Less firmly establishecI, however, is the contribution to human cancer of other naturally occurring chemicals present at tow levels in the foot!
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on initia tion, promotion, and progression of tumors." Further, the com mittee was charged to "focus on the toxicologic information avail able for natural substances" ant! to "develop a strategy for selecting adclitional natural substances for toxicological testing." In this report, the "initiation, promotion, and progression" stages of carcinogenesis were considerec!
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First, the committee concluded that based upon existing exposure clata, the great majority of individual naturally occurring and synthetic chemicals in the diet appears to be present at levels below which any significant adverse biologic effect is likely, and so low that they are unlikely to pose an appreciable cancer risk.
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Second, the committee conclucled that natural components of the diet may prove to be of greater concern than synthetic compo nents with respect to cancer risk, although adclitional ev~clence is required before definitive conclusions can be drawn. Existing con centration and exposure ciata and current cancer risk assessment methods are insufficient to definitively address the aggregate roles of naturally occurring and/or synthetic dietary chemicals in hu man cancer causation and prevention.
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In part, this may reflect the limited number of studies performed. Human epidemiologic data indicate that diet contributes to a significant portion of cancer, but the precise components of diet responsible for increased cancer risk are generally not well under stood.
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. IncleecI, at the present, quantitative statements cannot be macle about cancer risks for humans from specific dietary chemicals, either naturally occurring or synthetic.
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It is likely that there is also con siderable interindividual variation in susceptibility to specific chemicals or mixtures due to either inherited or acquired factors. Synthetic Versus Naturally Occurring Carcinogens Overall, the basic mechanisms involved in the entire process of carcinogenesis from exposure of the organism to expression of tumors are qualitatively similar, if not identical, for synthetic and naturally occurring carcinogens.
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in part on this limited sample, the committee conclucled that there is no clear difference between the potency of known naturally occurring anct synthetic carcinogens that may be present in the human diet. Of the selected agents tested, both types of chemicals have similar mechanisms of action, similar positivity rates in rodent bioassay tests for carcinogenicity, ant} encompass similar ranges of carcino genie potencies.
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RECOMMENDATIONS Numerous and extensive gaps in the current knowledge base were apparent as the committee endeavored to examine the risk of human cancer from naturally occurring versus synthetic compo nents of the diet. These gaps are so large and resources are so limited-that careful prioritization of further research efforts is essential.
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Additional data on the concentrations of naturally occurring and synthetic chemicals in foods and human exposures to them are needed. To determine exposures to specific dietary chemicals, it is necessary to know the concentration of a specific chemical in indi victual food commodities, as well as the patterns of consumption of those foot!
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In addition, human exposures to individual naturally occurring or synthetic chemicals are far lower than experimental test con ditions. (The committee recognized that of the NTP bioassays netting positive results, only 6% were from test levels exclusively at the maximum tolerated dose.)
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Selected addition al substances shouIcl be subjected to appropriate testing in order to develop a more comprehensive database on which to base corn parisons of the potential cancer risks or protective effects of natu rally occurring and synthetic chemicals in the diet. Because re sources for toxicological testing are limited and because there is a vast number of naturally occurring dietary chemicals, further test" ing of appropriately selected naturally occurring food chemicals requires the establishment of selection criteria.
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Possible mechanisms that have been implicated include increased cell proliferation, decreased cell cleath, changes in hormonal sta tus, and alterations in the activity of enzymes which metabolize enclogenous and environmental agents, ant! increased oxiciative
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Cons cerning specific plant derived chemicals, we do not have adequate information to recommend supplementation beyond the recom mencled daily requirements for particular vitamins or other nutri ents. FUTURE DIRECTIONS New research approaches and enhanced resources are neeclecI to address the precise roles of both naturally occurring and synthetic dietary chemicals in human cancer causation and prevention.
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As noted earlier, our diets are one of the most complex mixtures to which we are exposed. As an example, epidemiologic studies will become far more informative when they routinely employ improved biologic markers for exposure, indivicl ual susceptibility, ant!
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Finally, as advances are made in identifying with certainty spe cific naturally occurring dietary chemicals that either enhance or inhibit cancer risks in humans, it will be possible to formulate rational dietary guidelines for the American public. It may also be possible to use this information to mollify the composition of our foot!
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