The role of iron in metabolism, iron fortified foods

Iron plays a central role in metabolism. Enzymes containing iron take part in respiration, in photosyntheses, and in carbon and nitrogen metabolism as well. Bioavailability of iron is limited mostly by the solubility of its inorganic salts. At neutral pH the soluble ferrous-salts are polimerizating and become insoluble ferric-hydroxide. Living beings have developed effective mechanisms to mobilize iron. Solubility can be greatly improved by reducing pH or by producing chelating agents. There are two basic types of Fe3+ absorption mechanisms. (1) Specific siderophore system and (2) general reductive system. In iron-deficient environment certain microorganisms produce compounds called siderophores. These compounds keep Fe3+ in soluble form even at neutral pH. Elements of the reductive system have also been detected in Saccharomyces cerevisiae. It is suggested that both systems are present in most organisms. In human body most part of the iron is absorbed in the duodenum. More than half of the absorbed amount gets into the blood circulation, the rest is stored in the cells as ferritin. There is no free iron in the body, presumably because of its toxic character. The iron balance of the organism is determined by the amount of stored iron. The human body normally contains 4-5 g iron. 2.5-3.0 g is in the blood, and 0.8-1.5 g is in stored form. In lack of iron first the body runs out of stored iron then the number of blood cells and their haemoglobin content is being reduced. This state is called anaemia. There are two types of iron in the food: haem iron and non-haem iron. 25 of the haem and only 5 of the non-haem iron can be absorbed. Experiments have proved that the presence of vitamin C greatly induces the absorbtion of non-haem iron. On the other hand egg phosfitin, fibers, fitin acids, tannic acid (in tea), and calcium salts impede the absorption. Iron deficiency can be prevented by iron fortification of foods. In the past 30 years this has become a routine practice in the developed countries. They add iron salts (ferrous-succinate, ferrous-lactate, ferrous-glutamate, etc.) to rice, flour, salt and baby food. In England and in the USA the wheat flour is fortified with 1.65 mg/100g and 3.5 mg/100g iron respectively