Question

Describe two factors that affect iron absorption.

Answer 1

Two factors that affect absorption of iron are:

1. Dietary intake of iron: Iron is absorbed in small intestine from food by the enterocytes. Iron that is absorbed by enterocytes is the non-heme iron. Only 1-10% of this non heme iron is absorbed as it has less bioavailability. Moreover, non-iron heme should be reduced from Fe3+ to Fe2+ state to be absorbed to increase its solubility. This reduction occurs by ascorbic acid (vitamin c) and endogenous ferri-reductases. Meats only contain 5-10% heme iron. However, nearly 20-30% of this heme iron is absorbed due to its high bioavailability.

Ascorbic acid thus, enhances iron absorption. Other compounds include citric acid, carotenes, alcohol also increase absorption of non-heme iron. Gastric production by meat also increases non-heme iron absorption. There are certain dietary factors that inhibit iron absorption from food. These include phytic acid and polyphenols, which can bind to non-heme iron and prevent its absorption. Phytic acid is present in food grains and cereals while polyphenols is present in some vegetables, coffee, tea, and wine. Phytic acid is negatively charged and can bind to iron, which is positively charged. Calcium present in food also inhibits the absorption of non-heme and heme iron.

2. Erythropoiesis and body stores of iron: Erythropoiesis is the formation of red blood cells from a hematopoietic cell. Red blood cells require iron from incorporation into hemoglobin that has heme moiety. When there is an increase in erythropoiesis, plasma iron turnover also increases. This leads to increased absorption of iron in gastrointestinal tract to meet demands. Transferrin (iron binding proteins) and erythropoietin are speculated to be involved in this mechanism. Ferritin is present in intestinal walls. This ferritin will release iron to meet demands of erythropoiesis. Such breakdown of ferritin is seen in hemorrhage, iron deficiency anemia, high altitude or injection of erythropoietin.