Human Iron Metabolism - Body Iron Stores

Body Iron Stores

Most well-nourished people in industrialized countries have 4 to 5 grams of iron in their bodies. Of this, about 2.5 g is contained in the hemoglobin needed to carry oxygen through the blood, and most of the rest (approximately 2 grams in adult men, and somewhat less in women of childbearing age) is contained in ferritin complexes that are present in all cells, but most common in bone marrow, liver, and spleen. The liver's stores of ferritin are the primary physiologic source of reserve iron in the body. The reserves of iron in adults in industrialized countries tend to be lower in children and women of child-bearing age, than in men and in the elderly. Women who must use their stores to compensate for iron lost through menstruation, pregnancy or lactation, have lower non-hemoglobin body stores, which may consist of 500 mg, or even less.

Of the body's total iron content, about 400 mg is devoted to cellular proteins that use iron for important cellular processes like storing oxygen (myoglobin), or performing energy-producing redox reactions (cytochromes). A relatively small amount (3–4 mg) circulates through the plasma, bound to transferrin. Because of its toxicity, free soluble iron (soluble ferrous ions Fe(II)) is kept in low concentration in the body.

Iron deficiency first attacks the storage iron in the body, and depletion of these stores is thought to be relatively non-symptomatic, although some vague and non-specific symptoms have been associated with it. Since so much iron is required for hemoglobin, iron deficiency anemia is the primary clinical manifestation of iron deficiency. Oxygen transport is so important to human life that severe anemia harms or kills people by depriving their organs of enough oxygen. Iron-deficient people will suffer or die from organ damage well before cells run out of the iron needed for intracellular processes like electron transport.

Macrophages of the reticuloendothelial system store iron as part of the process of breaking down and processing hemoglobin from engulfed red blood cells.

Iron is also stored as a pigment called hemosiderin in an apparently pathologic process. This molecule appears to be mainly the result of cell damage. It is often found engulfed by macrophages that are scavenging regions of damage. It can also be found among people with iron overload due to frequent blood cell destruction and transfusions.