Iron is an important mineral element needed by all forms of life. It is most commonly found existing as Iron ॥ (Fe2+) or Iron॥। (Fe3+). Free iron can cause tissue damage; thus, in the body, Iron is bound to proteins and its concentration is tightly regulated especially because the body has no way of excreting excess iron. Such metalloproteins containing iron include heme proteins, transport /storage proteins and metalloenzymes. Heme is a group containing a porphyrin ring with an atom of iron at its core.
It is important in the transport of oxygen, which is carried bound to its Iron core. For this function, 4 molecules of the iron-bearing heme are coupled to 4 globin protein molecules (usually 2α and 2β globin chains) to form hemoglobin. Hemoglobin picks up oxygen from the pulmonary blood which has high oxygen content, low CO2 and high Ph, and drops it in the tissues which have low oxygen, high CO2 and low Ph. i.e. the Bohr Effect. One molecule of human hemoglobin can carry up to 4 molecules of oxygen.
Hemoglobin is mainly found in red blood cells. In fact, it is responsible for the red colour of blood. It is synthesized in maturing red cells; the heme part in the mitochondria and then cytosol, and the protein (globin) part in the ribosomes. Decrease in the synthesis of hemoglobin results in anemia. Anemia is defined as a decrease in the number of red blood cells or the amount of hemoglobin in the blood. The most common cause of anemia is iron deficiency. A low level of iron in the body negatively impairs the synthesis of hemoglobin and thus reduces the capacity of the blood to carry oxygen to tissues even in the presence of adequate oxygen tension.
Iron is obtained from food, absorbed in the gastrointestinal tract (mostly in duodenum) into enterocytes, taken across the enterocytes cell membrane by ferroportin, and transported in blood by transferrin to the bone marrow for red cell production, and to other tissues where it’s used. A small excess is stored as ferritin and hemosiderrhin. About 1mg of iron is lost daily in desquamated cells of skin and intestinal lining. This amount also corresponds to the amount absorbed from food daily even though the average diet contains up to 10-15mg of iron/day. The amount absorbed may however increase if there is an increase in the amount lost e.g. during bleeding. Sources of dietary iron include red meat, beans, lentils, black eyed peas, poultry, fish, green leafy vegetables, molasses and fortified foods like cereals. The animal sources contain heme iron (from blood and other hemoproteins) and non heme iron while the vegetable sources contain mostly non heme iron. Heme iron is easier to absorb than non heme iron which also requires ascorbic acid (Vit C) for absorption. Also, some substances such as phytates, oxalates, phosphates, carbonates, and tannates present in many plants such as grains, nuts, beans, spinach and lentils, chelate non heme iron and reduce its absorption. The presence of meat and vitamin c in a meal therefore improves the absorption of iron.
Iron deficiency can result from changes at different points on the iron metabolism journey.
