The estimation of vitamin A requirements necessitates the measurement of some physical or chemical criteria dependent on vitamin A intake. The known specific criteria which characterize a vitamin A deficiency in the animal organism have been summarized by Bessey and Wolbach.1 Of the several recognized signs of vitamin A deficiency, it now appears that hemeralopia, or partial night blindness, is the earliest to appear. Fortunately it is a condition which lends itself readily to physical measurement. The amount of vitamin A that will just prevent hemeralopia probably represents something a little less than the minimum requirement. Certainly the vitamin A intake should not fall below the level that will be sufficient to prevent night blindness. A liberal margin of safety should be allowed for physiologic variations and for enabling the organism to lay by a store of this vitamin against such emergencies as illnesses attended with low or restricted
BOOHER LE. VITAMIN A REQUIREMENTS AND PRACTICAL RECOMMENDATIONS FOR VITAMIN A INTAKE. JAMA. 1938;110(23):1920–1925. doi:10.1001/jama.1938.62790230008013
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