New perspectives on vitamin D.

Our perception of vitamin D has evolved since the early part of this century. As an active, dihydroxylated metabolite vitamin D is acknowledged today not as an essential dietary factor but rather as a major calciotropic hormone. This paper summarizes current understanding of the formation and action of vitamin D in health and disease. The importance of laboratory assessment of serum vitamin D metabolites in the diagnosis and management of disorders of calcium and phosphorus metabolism is discussed.