OCCURRENCE OF THE VITAMINS A 687 



feeding has been suspended. A similar suppression of carotenoid pig- 

 ments in hen eggs occurs Avhen massive doses of vitamin A are given to the 

 laying hen.^"' 



(Colostrum, also, has a considerably higher content of vitamin A than has 

 mature milk. The higher content is the result of the augmented levels of 

 both carotene and vitamin A. These results are beautifully illustrated in 

 the data of Gillam et al.,^^^^ given in Table 7. These results confirm the ear- 

 lier findings of Danni**^ and of Semb et al. ^"^ 



The vitamin A content of human milk varies with the period during lacta- 

 tion; it can also be considerably augmented by vitamin A supplementation. 

 Hrubetz ef a/.^°^ reported values ranging between 331 and 170 I.U. per 100 

 milliliters at varying times during the progression of the lactation cycle. 

 After the ingestion of 100,000 or 200,000 I.U. daily, the average was mark- 

 edly increased. The maximum value found Avas 2160 I.U. per 100 milli- 

 liters. 



(7) Vitamin A in Egg Yolk 



Another common source of vitamin A is the hen egg. In this case the 

 vitamin A is present entirely in the j^olk. The amount also varies with 

 diet. Sherman^^" reported values of 2,500 to 5,000 I.U. per 100 grams of 

 yolk; this amounts to 400-800 I.U. per 16 grams, which is the weight of the 

 yolk of the average-sized egg. Russell and Taylor^ ^^ give the value as 500- 

 800 I.U. per yolk, while Deuel et al.''^ report values of 800-900 I.U. of total 

 vitamin A per 18 grams of yolk for all groups of birds given supplemental 

 vitamins A up to levels of 15,000 I.U. of vitamin A per pound of ration fed. 

 When the diet contained 200,000 I.U. per pound of total food, the average 

 total vitamin A content of the yolks was reported as 2,170 I.U. per egg. 

 Thus, increased dietary vitamin A can produce an increase in the vitamin A 

 content of the egg. 



(8) Vitamin A in the Free and the Esterified Form 



Although vitamin A occurs in nature chiefly in the form of its esters, it 

 may likewise be present as the free alcohol. ^^^"^ Vitamin A palmitate has 



io« A. E. Gillam, I. M. Heilbron, W. S. Ferguson, and S. J. Watson, Biochem. J., 30, 

 1728-1734(1936). 



'«" W. J. Dann, Biochem. J., 27, 1998-2005 (1933). 



i"* J. Semb, C. A. Baumann, and H. Steenbock, /. Biol. Chem., 107, 697-703 (1934). 



1"' M. C. Hrubetz, H. J. Deuel, Jr., and B. J. Hanley, /. Nutrition, 29, 245-254 (1945). 



^1" H. C. Sherman, Chemistry of Food and Nutrition, 7th ed., Macmillan, New York, 

 1947, p. 634. 



"1 W. C. Russell and M. W. Taylor, ,/. Nutrition, 10, 613-623 (1935). 



112 A. L. Bacharach and E. L. Smith, Quart. J. Pharm., 1, 539-545 (1928). 



"3 L. Reti, Compt. rend. soc. biol., 120, 577-580 (1935). 



