IX. RKQUIREMENTS 



173 



as follows: 



TABLK XXII 

 Recommended Daily Dietary Allowances of Vitamin A» 



" Based on the assumption that two-thirds of the intake is provided as carotene, and that carotene 

 has one-half or less than one-half the biological value of vitamin A. 



The recommended allowance for the average adult (5000 I.U. from com- 

 bined sources) represents the equivalent of about 3250 I.U. of vitamin A, 

 or 6500 I.U. of carotene, if either provided the entire requirement. This is 

 in reasonable accord with the results of the Sheffield experiment,^* on the 

 basis of which 2500 I.U. of vitamin A or 7500 I.U. of carotene were the 

 recommended levels of requirement for young adults. The recommended 

 daily recjuirements are at least twice the minimal needs to prevent any 

 manifestation of avitaminosis A. The therapeutic requirements to resolve 

 clinical evidence of avitaminosis A are usually accepted as at least twenty 

 times the minimal need, i.e., about 50,000 I.U. 



All forms of vitamin A are absorbed well bj^ healthy individuals, but 

 natural vitamin A esters are not as effectively absorbed as are finely emul- 

 sified esters or the alcohol form in oil or in aqueous dispersion. These modi- 

 fied forms of the vitamin have greater therapeutic value than the unemul- 

 sified ester where intestinal absorption is below par."- ^^ Since 

 approximatelj' 99 % of vitamin A in the diet and in fish liver oil preparations 

 is in the form of natural esters, the factor of differential absorption of 

 different forms of the vitamin requires little consideration in meeting re- 

 quirements for vitamin A in the normal individual. 



"A. B. McCoord, C. P. Katsanipes, C. F. Lavender, F. J. Martin, R. A. Ulstrom, 



and R. H. TuUy, Pediatrics 2, 652 (1948). 

 f** C. D. May and C. U. Lowe, J. Clin. Invest. 27, 226 (1948). 



