Iron deficiency anemia is the most common form of anemia. Iron is an essential component of the hemoglobin molecule: without iron the bone marrow is unable to produce hemoglobin. The red cell count falls and those which do enter circulation are smaller than normal (microcytic) and lacking in hemoglobin, hence they are pale (hypochromic). The deficiency of iron may be absolute (there is no iron available for the production of hemoglobin - this is true iron deficiency anemia) or relative (the iron is present in storage in the marrow but other reasons prevent its incorporation into red blood cells). Iron deficiency anemia is usually easy to resolve. An anemia that does not respond as expected may require the help of a hematologist and additional testing. Development of anemia
It must be remembered that anemia in iron deficiency develops slowly. The type and severity of the anemia varies with time. The development stages are:
   1. Depletion of iron stores, decreased ferritin levels, no anemia
   2. Increased transferrin levels, no anemia
   3. Fall in serum iron, no anemia
   4. Development of normocytic, normochromic anemia
   5. Development of microcytic, hypochromic anemia.

Iron requirements
The average amount of iron in the average adult male is 4gm and in the average adult female 2.5gm. The normal North American diet contains approximately 15-20mg of iron per day. Most is present in meat and green vegetables; approximately 1.0mg is absorbed each day and just about an equal amount is lost in feces and sweat. As a result, the average adult's iron intake is in delicate balance, but is of little consequence as there is slightly more iron absorbed than lost and a store of iron is gradually accumulated. If for some reason the rate of iron loss increases, these stores can be depleted and an absolute iron deficiency develops. Such a deficiency requires large doses of supplemental iron to resupply the body stores and sufficient monitoring to prevent iron overload.

Iron absorption is increased by the presence of sufficient stomach acid, glucose, fructose, some amino acids and ascorbic acid (vitamin C). These substances aid in the absorption process by either reducing ferric iron to the ferrous state or by helping bind the iron to the mucosal cell receptor sites. The established benefit of vitamin C has resulted in many iron supplements being manufactured with this vitamin present. Heme iron (iron from meat myoglobin) is 10 times more easily absorbed than elemental iron, or iron from non-meat sources. Iron absorption is decreased by the presence of phosphate, bicarbonate or bile acids. Thyroid medication and iron supplements should be taken at different times of the day.

The adult male requires approximately 1.0mg per day, just enough to cover normal iron loss. The adult female requires approximately 2.0mg per day, enough for daily loss and menstruation. Pregnant females require approximately 3.0mg, enough for normal, ongoing loss and fetal requirements. Children require approximately 2.0mg, enough for normal loss and extra to produce some residual iron stores and allow for increasing red cell mass.

Causes of iron deficiency
   - Diet - uncommon except in children
   - Failure to absorb
   - Increased utilization (for example pregnancy, adolescent growth)
   - Atransferrinemia
   - Failure to utilize (for example lead poisoning, chronic diseases)
   - Blood loss.
Chronic blood loss is the most common cause of iron deficiency anemia.