Iron metabolism

Iron in foods can be in two forms. It can be in the form of a heme group or it can be in the form of a simple iron ion (Fe2+ or Fe3+). The two forms are absorbed by different mechanisms. Iron in meat is in the heme form while iron in non-meat foods is in the iron ion form. The heme form is easily absorbed; the absorption of the ion form can be decreased by many factors, like simultaneous intake of calcium (dairy products) or tea and can be increased by consumption of vitamin C. Normal gastric pH is needed for proper absorption of non-heme iron.

Iron is toxic to cells and must be stored inside cells as part of the ferritin protein. It is transported in the blood in the form of transferrin. Cells which need iron express a transferrin receptor on their cell surface. Transferrin binds to this receptor, and the transferrin-transferrin receptor complex is endocytosed. A soluble transferrin receptor, which is not attached to the cell surface but rather dissolved in the serum, also exists.