Iron deficiency anemia is a well-known and all-too-common problem, even with our modern knowledge about the condition and the attention given to preventing it. The preanemia state is not easy to diagnose. Decreasing iron stores and a relative decrease in serum iron levels and protein-bound iron may cause symptoms before low tissue iron levels or anemia are measurable. More of this important mineral is needed during growth; iron deficiency is more common in infancy, childhood, adolescence, and pregnancy. Even the elderly may become deficient due to poorer absorption and diet. Women in their reproductive years have a greater problem with iron deficiency because of losses in menstrual blood and higher requirements. Minority and low-income people tend to have a higher incidence of low iron-related problems, primarily caused by dietary deficiency. Women in their childbearing years require at least 18 mg. of iron daily, but more than 25 percent of them probably obtain less than this amount. Usually, when the body needs more iron, absorption improves through an increase in iron-carrying proteins in the blood, called iron transferrin.
Iron absorption from the intestinal tract is a very subtle process; poor absorption is one of the main reasons, along with low-iron diets, that iron deficiency is so prevalent. Along with calcium, which is also difficult to absorb, iron and zinc are the minerals most commonly deficient in our diet.
Average iron absorption is about 8-10 percent of intake. All vegetable sources contain the "nonheme" form of iron, which is poorly absorbed and utilized. "Heme" iron, a special formulation of iron, is found only in flesh foods, beef and liver being the best sources. Between 10 and 30 percent of heme iron is absorbed. Combining heme foods with nonheme foods improves the absorption of iron from the nonheme foods. This is why complete vegetarians have trouble obtaining sufficient iron from the diet alone. Phytates present in whole grains and oxalates found in certain vegetables may bind up some of the iron and make it unabsorbable. Meat foods improve absorption, possibly by stimulating increased stomach acid production and by the fact that the iron contained is already bound into muscle and blood tissue, the iron proteins myoglobin and hemoglobin.
Iron absorption is a slow process, usually taking between two and four hours. The food-natural ferrous (+2) ion is absorbed much better than iron in the ferric (+3) form. Vitamin C in the gut along with iron converts any ferric iron to ferrous and thus improves absorption. Iron absorbed into the blood is usually bound to the protein transferrin and goes mainly to the bone marrow, where it can be used to make red blood cells. Some also goes to the liver and spleen. About 25 percent of body iron is stored bound to the protein ferritin and as the iron complex hemosiderin. Ferritin has good iron-binding capacity. A fully saturated ferritin molecule, which is actually ferric oxide surrounded by the protein apoferritin, can contain about 4,000 iron atoms. Ferritin stored in the liver, spleen, and bone marrow, for example, provides a good reserve of iron to meet body needs. Measuring serum ferritin levels is a fairly new medical test that provides a good indication of iron storage levels. A normal value is 15-200 mcg. A level below 15 mcg. suggests very depleted iron reserves. Iron toxicity may show ferritin levels in the thousands.