The total body iron in a 70-kg man is about 4g. This is maintained by a balance between absorption and body losses. Although the body only absorbs 1mg daily to maintain equilibrium, the internal requirement for iron is greater (20-25mg). An erythrocyte has a lifespan of 120 days so that 0.8% of red blood cells are destroyed and replaced each day. A man with 5 L of blood volume has 2.5 g of iron incorporated into the hemoglobin, whith a daily turnover of 20 mg for hemoglobin synthesis and degradation and another 5 mg for other requirements. Most of this iron passes through the plasma for reutilization. Iron in excess of these requirements is deposited in body stores as ferritin or hemosiderin.