Calcium, phosphate, and vitamin D.

It is evident that there has been enormous progress within the last decade in our understanding of vitamin D metabolism and its interaction with calcium, phosphate, parathyroid hormone, and a number of other factors. As a result largely of therapeutic trials with various metabolites of vitamin D, we now know something of their probable involvement in the development of rickets and osteomalacia. We do not yet have a clear comprehension of exactly how these metabolites influence bone mineralization other than through their indirect effect on serum calcium and phosphate. Nonetheless it seems likely that at least one, and perhaps more, of the metabolites do exert a more direct effect. One must conclude that a deficiency of the 1alpha-hydroxylase is probably not the only defect in renal insufficiency, although it currently that there must well known. It is premature to go so far as to suggest that there must be another metabolite not being synthesized in the diseased or absent kidney.