Evaluation of Vitamin D3 Supplements by Biological Assay Using the Turkey

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Abstract
Twenty-six vitamin D3 supplements were assayed biologically using the young turkey. Four of the samples showed low relative biopotencies, i.e., 38.9, 40.1, 41.9, and 55.8%, using bone ash as the response criterion. Nineteen of the samples were satisfactory (above 80%). The respective average chemical assay values for the four low samples were 223, 91, 85, and 114% of stated potencies. The results of chemical assay did not reflect the biopotencies accurately, suggesting that the USP chemical assay measures biologically inactive as well as active compounds. In an additional study, 22 vitamin D3 supplements were assayed biologically using toe ash as the response criterion. Nine of the samples had significantly lower biopotency than the standard; of these, three were under 60%. Several biological response criteria were compared in a study of assay precision and correlation. Growth; femur bone ash; bone length, breaking strength, and rigidity; plasma alkaline phosphatase; and plasma inorganic phosphorus correlated well with vitamin D status. Bone ash gave the greatest assay precision.