The Role of Iron in Human Nutrition
Structure, Function and Metabolism of Dietary Iron
Iron is a trace element, which is a group of minerals present in small quantities in the body. Other trace elements include copper, zinc, selenium, manganese and iodine. These minerals cannot be synthesized by the body and must therefore be supplied in the diet. Iron is the most common trace element in the human body; adult males have approximately 3.5 g iron in total, or 50 mg per kg body weight while females have about 2g total iron or 35 mg per kg bodyweight. Iron can exist in oxidation states from -2 to +6, but mainly exists in the ferrous (+2) and ferric (+3) states in biological systems. As iron has the ability to accept and donate electrons readily,
Before haem iron can be absorbed, it must be hydrolysed from the globin part of haemoglobin or myoglobin; this is carried out by proteases in the stomach or small intestine. Once the haem is released from the globin, it is absorbed across the mucosal cells of the small intestine by haem carrier protein 1 (HPC1). Once absorbed, the haem molecule is hydrolysed into inorganic ferrous iron and protoporphyrin by haem oxygenase, and can be used by the intestinal cell, excreted or used by other tissues. Non haem iron must be released from food components in order to be absorbed, this process is aided by gastric secretions such as hydrochloric acid and proteases in the stomach and. Following its release from food, the non-haem iron is present in its ferric form in the stomach. Although ferric iron remains soluble in an acidic environment such as the stomach, once it passes into the small intestine it is exposed to alkaline juices excreted from the pancreas into the intestine. In this more alkaline environment, the ferric iron may form a ferric hydroxide complex, which usually aggregates and precipitates, thus becoming difficult to absorb. To prevent this, ferric iron must be converted to its ferrous form which remains soluble at an alkaline pH. There are enzymes located on the intestinal brush border known as ferrireductases which reduce ferric iron to the more soluble ferrous state. Once reduced, the ferrous iron is then transported across the mucosal cells by the transporter protein divalent metal cation transporter 1