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Biological Availability of Fat-Soluble Vitamins: Vitamin A and Carotene^{1, 2,}

Michigan State University, East Lansing³ 48823

Abstract

Chemical analysis of the diet for its concentration of fat-soluble vitamins does not establish biopotency. This is true because certain widely-used chemical assays tend to lack specificity, while biopotency is dependent on precise and specific structural and stereochemistry. In addition, the presence or absence of other substances in the diet may influence the efficiency with which these vitamins are absorbed and metabolized. Significant differences in vitamin utilization between species and between individual animals, coupled with differing quantitative requirements dependent upon the criterion chosen, also contribute to the discrepancy between biopotency and chemically determined concentration. The significance of these factors is illustrated by the finding that 1 mg of corn carotene, which would have 1,667 IU of vitamin A activity if it were all-trans-ß-carotene and were fed to rats under appropriate conditions, has 500 IU of vitamin A activity for the pig according to the National Research Council, or 261 IU of vitamin A activity according to research by the author and his associates. It is clear that chemical assay is not an entirely adequate substitute for bioassay, and extension of laboratory findings of dietary vitamin potency to the living animal should be made with care.

¹ Published with the approval of the Director of the Michigan Agricultural Experiment Station as Journal Article No. 5672.

² Presented at the 63rd Annual Meeting of the American Society of Animal Science, University of California, Davis, August 4, 1971, as part of a Symposium on Biological Availability of Nutrients in Feeds. Co-sponsored by the A.S.A.S. and the Committee on Animal Nutrition, N.A.S./N.R.C.

³ Department of Animal Husbandry, College of Agriculture and Natural Resources.