OCCURRENCE OF VITAMINS D 775 



The concentration of vitamin D in milk is increased by several methods 

 in commercial practice. One of these involves a direct addition of vitamin 

 D concentrate to milk, to yield a potency of 150 or 300 I.U. per quart. ^^^-^^^ 

 Propylene glj'col is frequentl}^ employed as a solvent. A second procedure 

 of little importance commercially because of the sHght effectiveness is 

 the direct irradiation of the cow with sunlight or with artificial ultraviolet 

 light. "^'^^^ However, the potency of cow milk may be increased from 5 

 I.U. per quart in the unirradiated animals to 17-26 I.U. per quart,^^^ or 

 even as high as 44^^^ I.U. after the animals have been exposed to sunlight. 



One of the most widely employed methods for the augmentation of the 

 vitamin D content of milk entails the feeding of large doses of irradiated 

 yeast to the cows. When the quantities of such vitamin D administered 

 are controlled, a so-called "metabolized" vitamin D milk is produced which 

 contains a minimum of 400 I.U. per quart. Some years ago Krauss and 

 Bethke^^^'^^® demonstrated that the vitamin D content of milk is increased 

 by feeding irradiated ergosterol to the cows. Irradiated yeast feeding was 

 later shown to be even more effective. ^"-^^^ A cod liver oil concentrate, 

 Vitex, was also fed, with good results. ^^^ The ewe, likewise, has been shown 

 to respond to feedings of irradiated yeasts and molds by producing milk 

 with an increased vitamin D content, while irradiated ergosterol was found 

 to be less effective in producing this increase, ^^^ when fed in equivalent 

 amounts. 



Still another procedure for the production of high vitamin D milk em- 

 ploys the direct irradiation of the milk. While this is the cheapest method, 

 it is also the most difficult one with which to produce satisfactory results, 

 as over-irradiation produces milk with an unpleasant taste and odor.^^^ 

 Specific methods which have been proposed to overcome this difficulty 

 have been reviewed by Diemair.^^^ There is a sufficient amount of pro- 

 vitamin D in milk to allow for a maximum production of 200 I.U. per 

 quart; however, the vitamin D level in commercial irradiated milks has 

 been standardized to a vitamin D content of 135 I.U. per quart. 



The eggs of most birds are also good sources of vitamin D. It occurs ex- 



2" T. F. Zucker, Am. J. Pub. Health, 23, 10-18 (1923). 



2" D. J. Barnes, /. Mich. State Med. Soc, 22, 242-246 (1933). 



235 W. E. Ivrauss and R. M. Bethke, J. Biol. Cfiem., 92, x-xi (1931). 



236 W. E. Ivrauss, R. M. Bethke, and C. F. Monroe, /. Nutrition, 5, 467-477 (1932); 

 Ohio Agr. Exptl. Sta., Bimonthly Bull, No. 156, 117-121 (1932). 



2" B. H. Thomas and F. L. MacLeod, Science, 73, 618-620 (1931). 



238 W. E. Krauss and R. M. Bethke, Ohio Agr. Exptl. Sta., Bimonthly Bull, 18, No. 

 162, 77-80 (1933). 



239 W. E. Ivrauss, R. M. Bethke, and M. Wilder, Ohio Agr. Exptl Sta., Bimonthly Bull, 

 18, No. 1, 15-19 (1933). 



2'» W. O. Kirk, Iowa SUite Coll J. Sci., 13, 235-238 (1939). 



2" K. G. Weckel and H, C. Jackson, Food Research, 1, 419-426 (1936). 



2'2 W. Dieniair, Chem. Fabrik, 14, 51-54 (1941). 



