Vitamin D in Milk–A Review

INTRODUCTIOI~The introduction of vitamin D milk was based upon nutritional facts: (a) that an antirachitic factor is necessary for proper generation, growth and maintenance, (b) that this factor is lacking in dietary products normally used, including normal cow's milk, (c) that living standards precluded availability to humans of the natural agents by which the factor might be generated, (d) that milk contained the balance of a necessary nutritional triad, vitamin D, calcium and phosphorus, and (e) milk is generally available where there is need for the additional factor.While these facts may be evident to the student who has reviewed the subject, less evident facts need some explication.The creation of a vitamin fortified milk simultaneously brought with it merchandising problems.Among these may be cited (a) the necessity of translation and transfer of knowledge of the biological laboratory and its precise and complicated terms into acceptable form for reading matter, radio and minds of the distributor salesmen and consumer (b) by inference there was tacit admission publicly of an inadequacy of cow's milk as a "perfect" food and (c) the change in equipment and processing methods, as well as prevailing regulations required a premium charge for the new vitamin-milk product. Variation of Vitamin D in Milk.The preformed antirachitic quality of cow's milk is affected by secretory processes, feed quality and animal management.While the quantity occurring naturally in milk is far less than demanded by human dietary requirements, the variations and sources of the factor are of practical significance. Range in Variations.The extreme spread of a number of reports of variations in the natural vitamin D content of milk is from 3.1 to 56.0 U.S.P. units per quart, a variation of some 18 fold..An average of the minimum and maximum levels cited in these studies is 19.3 and 31.7 U.S.P. units per quart, a variation of 1.6 fold.The amounts cited include variations due to the method of preparing the sample for assay, and the interpretation of the assay.Reference to factors affecting the variations in content of vitamin D in milk are of greater interest.This was excellently reviewed by Olson and Wallis (84). Effect of Ration.While there have been a significant number of studies on the effect of several factors on the vitamin content of milk, the methods and results of most are insufficient to demonstrate the effects only of feed