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Anomalies in the Bio-Assay of Vitamin D Milk

Department of Biochemistry, and The Institute of Optics, University of Rochester, Rochester, New York

Experiments have been described which show that skimmed milk which has been fortified with vitamin D by the addition of concentrates exhibits, on bio-assay, an enhanced apparent potency which is approximately three times greater than the value expected, based on the amount of concentrate added. Furthermore, it is shown that feeding the concentrate and the skimmed milk separately to the same rats results in less enhancement of potency than does feeding the concentrate in the form of fortified skimmed milk. Milk also enhances the potency of the international standard solution of vitamin D.

In discussing these results, it is pointed out that the response of the rachitic albino rat to certain dietary factors other than vitamin D is well known. The bio-assay of vitamin D milk may introduce several of these factors. In view of the conditions imposed by the usual curative assay procedure, the roles played by phosphorus and, possibly, lactose in the effective antirachitic action of vitamin D milk appear to deserve special attention in the future work on this problem.