What percent of the human body's iron is found in the red blood cells called hemoglobin and in muscle cells called myoglobin?

Iron is an essential element for blood production. About 70% of the body's iron is found in the red blood cells of the blood called hemoglobin and in muscle cells called myoglobin. Hemoglobin is essential for transferring oxygen in blood from the lungs to the tissues. Myoglobin, in muscle cells, accepts, stores, transports and releases oxygen.

About 6% of body iron is a component of certain proteins, essential for respiration and energy metabolism, and as a component of enzymes involved in the synthesis of collagen and some neurotransmitters. Iron also is needed for proper immune function.

About 25% of the iron in the body is stored as ferritin, found in cells and circulates in the blood. The average adult male has about 1,000 mg of stored iron (enough for about three years), whereas women on average have only about 300 mg (enough for about six months). When iron intake is chronically low, stores can become depleted, decreasing hemoglobin levels.

When iron stores are exhausted, the condition is called iron depletion. Further decreases may be called iron-deficient erythropoiesis and still further decreases produce iron deficiency anemia.

Blood loss is the most common cause of iron deficiency. In men and postmenopausal women, iron deficiency is almost always the result of gastrointestinal blood loss. In menstruating women, genitourinary blood loss often accounts for increased iron requirements.