I N 1958, BOTHWELL ET AL'published studies from which they concluded that both the size of iron stores and the rate of erythropoiesis influenced iron absorption in humans. More recent information on iron balance defines better the role of these two regulators. In individuals with normal essential body iron, the store-regulator is responsible for meeting normal iron loss as well as the additional requirements for growth and menstruation; it is also responsible for accumulating and controlling iron stores. Its capacity to change iron balance is less than 2 mg/day. In addition, there is an erythron-related regulator with a greater capacity. It acts more specifically to defend the production of red blood cells (RBCs) against a limiting iron supply, regardless of body iron balance. At present it is impossible to separate the respective contributions of absorption and excretion in the first of these processes, although absorption dominates the latter.

Iron balance in the normal adult male is limited, with an exchange of slightly less than 1 mg/dz 3 It is regulated so as to achieve a full complement of essential body iron and to accrue a reserve as a buffer against emergencies. This discussion will be concerned with the quantitative aspects of this regulation. Because menstruation and pregnancy impose large and variable requirements in the female, the focus will be on the male as a more uniform model for the study of iron balance.