Retinyl acetate biological activity

Free retinol is chemically unstable and does not occur to any significant extent in foods or tissues. Rather, it is present as a variety of esters, mainly retinyl palmitate. Retinyl acetate is generally used as an analytical standard and in pharmaceutical preparations. Dehydroretinol (vitamin A2) is found in freshwater fishes and amphibians it has about half the biological activity of retinol. 

The obsolete International Unit (iu) of vitamin A activity was based on biological assay of the ability of the test compound to support growth in deficient animals (1 iu = 10.47 nmol of retinol = 0.3 //g of free retinol or 0.344 //g of retinyl acetate). 

Vitamin A is a fat-soluble vitamin. The RDA for vitamin A is 1-0 mg of retinol, or its equivalent. The international unit [lU) is used to compare the biological activities of various sources of vitamin A- One iU of vitamin A activity can be supplied by 0.3 pg of all-ffiflMS-relinol, 0.344 pg of all-trans-retinyl acetate, or 0,60 pg of all-frens-p-carotene. 

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