The Biological Activity of Calciferol (Vitamin D 2 ). ∗

Abstract

Summary

Assays of 8 samples of calciferol (vitamin D₂) using the U.S.P. biological assay with rats indicated in every case a potency significantly greater than 40 U.S.P. units per μg. Our assays gave an average value of 49.7 ± 2.1 units per μg. This is interpreted to mean that U.S.P. reference cod liver oil No. 2 has less than its generally accepted potency. In view of this finding, a re-evaluation of the relationship between calciferol, the international standard and the U.S.P. standard for vitamin D would seem to be indicated. Serious consideration should be given to adopting a fixed weight of pure crystalline calciferol or vitamin D₃ as the legal unit instead of relying on designated weights of reference standards consisting of solutions of impure and possibly unstable mixtures.