Newer knowledge of vitamin D and its metabolites in health and disease.

Renewed interest in vitamin D, over the past several years, has resulted in increased knowledge of (1) the metabolic pathways which result in production of an active metabolite, (2) the role of its various metabolities at target tissues, and (3) its interaction with other control systems in the maintenance of calcium/phosphorus homeostasis. Presently, a role for 1, 25-(OH)2 D3 can be identified in the regulation of (1) calcium and phosphorus absorption from the intestine, (2) PTH production, and (3) calcium mobilization from bone (in conjunction with PTH). Several other actions at the kidney, muscle and other organs have been suggested but not proven. In contrast, the actual process of bone mineralization may be dependent, in part, on 25-(OH) D3. Despite these major advances in our knowledge, many gaps remain and controversial data continues unresolved. However, application of this new information to analysis of a wide variety of disease states has resulted in remarkable progress in appreciation of the pathogenesis and appropriate treatment for these diseases. Nonetheless, continued research promises further advances and more precise definition of disease states as well as delineation of the therapeutic role of Vitamin D metabolites in their treatment.