Diet, Nutrition, and Cancer (1982) / Chapter Skim
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9 Vitamins
9 Vitamins
Pages 138-161
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From page 138... ...
Epidemiological Evidence The impact of vitamin A on carcinogenesis is of considerable interest. Several epidemiological investigations, mostly case-control studies, have indicated an inverse relationship between vitamin A intake and a variety of cancers.
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After controlling for cigarette smoking and alcohol consumption, they found an inverse relationship (with a dose-response gradient) between cancer risk and indices of both vitamins A and C intake based on frequency of consumption of selected foods.
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Also consistent with these findings were observations of populations in the Caspian littoral of Iran (a region of particularly high esophageal cancer incidence) indicating that consumption of green vegetables and fresh fruit and estimated vitamin A and C intake in high risk areas were lower than in areas of low risk (Hormozdiari et al., 1975; Joint Iran-International Agency for Research on Cancer Study Group, 1977~.
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In organ cultures of hamster tracheas, vitamin A inhibited the induction of squamous cell metaplasia and proliferative epithelial lesions by benzo~a~pyrene (Cracker and Sanders, 1970~. Some _ viva experiments have produced similar results.
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Supporting data reported by Nettesheim and Williams (1976) indicated that vitamin A protects against 3-methylcholanthrene-induced squamous cell metaplasia and early neoplastic lesions of the lung in rats.
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Summary Epidemiological Evidence. A growing accumulation of epidemiological evidence indicates that there is an inverse relationship between the risk of cancer and the consumption of foods containing vitamin A (e.g., liver)
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Similar inverse associations between fresh fruit consumption or vitamin C intake and gastric cancer have been reported by Higginson (1966) , Haenszel and Correa (1975)
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(1981~. These investigators found an inverse relationship between cancer risk and indices of both vitamins C and A, after controlling for cigarette smoking and alcohol consumption.
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Overall, the reported protective effects of ascorbic acid on neoplasia are not impressive, except for those brought about through an indirect mechanism, i.e., the prevention of the formation of carcinogenic N-nitroso compounds. In only two instances have investigators reported inhibition of carcinogenesis in the same tissue, i.e., the large bowel (Logue and Frommer, 1980; Reddy and Hirota, 1979~.
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From page 147... ...
Furthermore, they provide mostly indirect evidence since they are based on the consumption of foods, especially fresh fruits and vegetables, known to contain high concentrations of the vitamin, rather than on actual measurements of vitamin C intake. The results of several casecontrol studies and a few correlation studies suggest that the consumption of vitamin-C-containing foods is associated with a lower risk for certain cancers, particularly gastric and esophageal cancer.
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From page 148... ...
Thus, the inhibitory effects of a-tocopherol would take place largely in a lipid milieu. There have been no in viva studies to determine the effects on neoplasia resulting from a-tocopherol-induced inhibition of nitroso compound formation.
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Although the tumor incidence was similar in both groups, the average number of tumors per animal was less in the high vitamin E group than in the low vitamin E group. Studies of the effects of vitamin E on carcinogenesis do not show severe or consistent inhibitory effects.
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In three of four experiments, however, the rate of tumor development was faster in mice ingesting moderate amounts of vitamins than in mice ingesting either high or low amounts. Boutwell _ al.
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The relative importance of the individual dietary components may vary, depending on experimental conditions. The relationship of the results of the short-term tests to those from in viva studies for carcinogenicity of chemicals in animals adds a further complication.
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Because of the interrelationships among the B vitamins and their relationships with other major dietary components, it is difficult to explain specifically the effects on promotional events (Diamond et al., 1980)
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1975. Dietary vitamin A and human lung cancer.
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1979. Oesophageal cancer studies in the Caspian littoral of Iran: Results of a case-control study.
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1980. Comparison of dietary histories in lung cancer cases and controls with special reference to vitamin A
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1977. Esophageal cancer studies in the Caspian littoral of Iran: Results of population studies -- a prodrome.
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1977. Risk factors for lung cancer in Singapore Chinese, a population with high female incidence rates.
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1975. Induction of mouse lung adenomas by amines or ureas plus nitrite and by N-nitroso compounds: Effect of ascorbate, garlic acid, thiocyanate, and caffeine.
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1975. Inhibitory effect of sodium ascorbate on ethylurea and sodium nitrite carcinogenesis and negative findings in progeny after intestinal inoculation of precursors into pregnant hamsters.
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1981. Dietary vitamin C and uterine cervical dysplasia.
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As 161 Wolbach, S
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