Abstract
VITAMIN A is unique in that the unit by which it has been defined has been measured with reference to a precursor, β-carotene, and not to vitamin A itself. This biological unit based on β-carotene as standard is cumbersome and subject to gross errors. Certain foodstuffs are now required by law to include vitamin A, and regulations require that foodstuffs, claiming to contain vitamins, be labelled in units, Manufacturers who to-day handle vitamin A are dependent on the spectroscopic method of assay using the extinction coefficient at 325–328 mμ as a linear function of vitamin A activity, and it has been necessary to adopt a factor to relate the spectroscopic reading with the biological international unit. Such factors have become standardized in Great Britain and in America although at different levels.
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Biological Unit for Vitamin A. Nature 155, 540–541 (1945). https://doi.org/10.1038/155540d0
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DOI: https://doi.org/10.1038/155540d0