REQUIREMENTS OF ANIMALS 589 



for normal adults is 5000 1.U., as provided by 4000 1.U. of carotene and 1000 

 I.U. of \'itamin A. The recommended daily allowances of vitamin A es- 

 tablished by the U. S. Food and Drug Achninistration'"""' are given as 1500 

 U.S. P. units for infants, 3000 U.S. P. units for children one to eleven years 

 of age, 4000 U.S.P. units for children over twelve years of age and for adults. 

 The recommended daily allowances of vitamin A as proposed by the Food 

 and Nutrition Board of the National Research Council are given in Table 

 12. 



b. Sex. It has long been recognized that the sex of the animal 

 is an important factor in the metabolism of the carotenoids and vitamins 

 A. Thus, in general, higher levels of /5-carotene obtain in the plasma of 

 women than in that of men, while the situation is reversed insofar as the 

 level of blood vitamin A is concerned. Moreover, the sex of the animal is 

 important in relation to the storage of vitamin A in the tissues, including 

 the liver and kidney. Females usually store more vitamin A in their 

 livers than do the males. However, in the experiments of Paul and 

 Paul,^^® in which the level of vitamin A intake and longevity were cor- 

 related, it was evident that given doses of vitamin A prolonged the life 

 span to a greater extent in females than in males. One may interpret this 

 to indicate a lower requirement in the female (see Table 10, page 581). 

 In general, the vitamin A requirements of the males and females are con- 

 sidered to be practically identical. Only during pregnancy and lactation 

 can it be demonstrated that the requirement of the female is increased ap- 

 preciably over that of the male. However, Week and Se\'igne^^^ observed 

 essentially different responses to test doses of vitamin A in women as com- 

 pared with men. 



c. The Administration in Aqueous Dispersions. The absorption of 

 vitamin A is considerably improved when it is administered in aqueous 

 dispersions,^^*"^^^'^^^ as compared with its utilization when given in oil 

 solutions ; hence smaller amounts of the vitamin A are required when it is 

 administered in water dispersion. Aqueous dispersions prove particularly 

 helpful in diseases associated with impaired absorption as, for example, 

 cehac disease, pancreatic fibrosis, and occlusion of the bile duct. It has 

 also been observed that chicks utilize vitamin A better, as indicated by 

 greater growth, when the vitamin is given in water emulsion rather than 

 in vegetable oil.^"" 



d. The Form of Vitamin A. Experiments designed to demonstrate pos- 



lois Anonymous, Federal Register, 6, Sect. 403 (j), Nov. 22, 1941, p. 5925; 1949 ed., 

 Code Federal Regulations, Title 21, Sect. 125.3 (4) (b) (1), p. 108. 

 '01-' G. R. Halpern and J. Biely, J Biol. Chem., 174, 817-826 (1948). 



