Factors affecting iron balance.

The availability of radioisotopes of iron led to the performance of physiologic studies of the absorption, excretion, and kinetics of iron. The effects of dietary constituents and intestinal secretions upon iron absorption have been thoroughly explored and have permitted the development of tools for nutritional studies in various geographic areas of the world. The basic mechanisms for regulation of iron absorption are not fully understood. However, the isolation and characterization of newer iron-binding proteins, the existence of mucosal receptors in which there is competition for iron-binding sites with other metals, and the identification of a number of animal models with genetic abnormalities of iron absorption provide promise for development in the foreseeable future. The means by which the body informs the intestine to increase or decrease iron absorption is poorly understood, and the abnormality in hemochromatosis and iron overloading disorders remains unexplained. Much has been learned in recent years regarding the structure of iron-containing proteins and the variations that exist in different species. Similar problems remain to be solved with regard to the intermediary metabolism of iron in red blood cell precursors and other cells in the body. It is postulated that the combined usage of physiologic, biochemical, and immunologic investigations will provide the basic information required.