472 IX. CAROTENOIDS AND VITAMINS A 



currence of the maximum blood level, in the case of normal human sub- 

 jects; 134,000 fxg. of vitamin A were given as the free alcohol, acetate or 

 natural ester in 50 g. margarine fat, to adult subjects. The highest plasma 

 levels were recorded after vitamin A alcohol had been fed, while somewhat 

 lower figures were noted when vitamin A acetate was the source of vitamin 

 A. The lowest vitamin A tolerance curves were noted after the natural 

 vitamin A esters were fed. These results are interpreted as indicative of 

 variations in the absorption of vitamin A as related to the form in which it is 

 administered. As noted earlier, although vitamin A alcohol constitutes 80 

 to 90% of the total plasma vitamin A of the fasting samples, it was found 

 to account for only 10% of the sample at the apex of the plasma vitamin A 

 curve. 



(6) Physiologic Factors Altering Blood Vitamin A. Age is an important 

 factor with which both plasma vitamin A and l)lood carotene can be cor- 

 related. Thus, a number of investigators have reported low values in the 

 newborn which increase to levels comparable with those in the adult during 

 the first year of life. Henley et al}^^ observed a value of only 20.4 /xg. % 

 (68 I.U.) in three-week-old premature babies, while Szymanski and Long- 

 welP°- noted the minimum plasma vitamin A in the case of infants two days 

 old (23 /ug. % or 77 I.U.). Lewis et al}^ reported a precipitous drop of 

 plasma vitamin A to 11.1 /ig- % (37 I.U.) within forty-eight hours after 

 birth. Progressively increasing levels have been noted during the first 

 year of life. Thus a maximum value of 56 /xg. % (168 I.U.) was observed 

 in the nine-month-old group by Szymanski and Longwell.'"^ Lewis 

 et al.^^^ recorded vitamin A values in the blood of older infants as 13.5 to 

 42.3 ng. % (45 to 141 I.U.). Robinson and co-workers^ ^^ reported values 

 between 30 and 36 /xg- % (100 and 120 I.U.) for children between six and 

 sixteen years of age. 



Slightly lower values than normal have been noted in the aged. Rafsky 

 et al.^^^ reported plasma vitamin A levels of 29.3 and 25 ng. % for aged 

 males and females (98 and 83 I.U.), respectively. Kirk and Chiefh^'- 

 eited somewhat lower figures for the plasma vitamin A in the oldest groups. 



Fetal levels of plasma and liver vitamin A are consistently considerably 

 lower than those of the mother. ^''■^~"- It has been suggested that the 



366 T. H. Henley, M. Dann, and W. R. C. Golden, A7n. J. Diseases Children, 68, 

 257-264 (1944). 



367 W. J. Dann, Biochem. J., 26, 1072-1080 (1932); 28, 634-637 (1934). 



368 W. Neuwiler, Z. Vitaminforsch., IS, 275-280 (1943). 



368 G. H. Wise, M. J. Caldwell, and J. S. Hughes, Science, 103, 616-618 (1946). 

 3™ C. J. Lund and M. S. Kimble, Am. J. Obstet. GxjnecoL, 46, 207-221 (1943). 

 3" J. Portes and J. Varangot, Compt. rend. soc. hioL, 136, 166-168 (1942). 

 3'2 J. N. Byrn and N. J. Eastman, Bull. Johns Hopkins Hosp., 73, 132-137 (1943). 



