tailieunhanh - Chapter 098. Iron Deficiency and Other Hypoproliferative Anemias (Part 3)

Nutritional Iron Balance The balance of iron in humans is tightly controlled and designed to conserve iron for reutilization. There is no regulated excretory pathway for iron, and the only mechanisms by which iron is lost from the body are blood loss (via gastrointestinal bleeding, menses, or other forms of bleeding) and the loss of epithelial cells from the skin, gut, and genitourinary tract. Normally, the only route by which iron comes into the body is via absorption from food or from medicinal iron taken orally. Iron may also enter the body through red-cell transfusions or injection of iron complexes | Chapter 098. Iron Deficiency and Other Hypoproliferative Anemias Part 3 Nutritional Iron Balance The balance of iron in humans is tightly controlled and designed to conserve iron for reutilization. There is no regulated excretory pathway for iron and the only mechanisms by which iron is lost from the body are blood loss via gastrointestinal bleeding menses or other forms of bleeding and the loss of epithelial cells from the skin gut and genitourinary tract. Normally the only route by which iron comes into the body is via absorption from food or from medicinal iron taken orally. Iron may also enter the body through red-cell transfusions or injection of iron complexes. The margin between the amount of iron available for absorption and the requirement for iron in growing infants and the adult female is narrow this accounts for the great prevalence of iron deficiency worldwide currently estimated at one-half billion people. The amount of iron required from the diet to replace losses averages about 10 of body iron content a year in men and 15 in women of childbearing age. Dietary iron content is closely related to total caloric intake approximately 6 mg of elemental iron per 1000 calories . Iron bioavailability is affected by the nature of the foodstuff with heme iron . red meat being most readily absorbed. In the United States the average iron intake in an adult male is 15 mg d with 6 absorption for the average female the daily intake is 11 mg d with 12 absorption. An individual with iron deficiency can increase iron absorption to about 20 of the iron present in a meat-containing diet but only 5-10 of the iron in a vegetarian diet. As a result one-third of the female population in the United States has virtually no iron stores. Vegetarians are at an additional disadvantage because certain foodstuffs that include phytates and phosphates reduce iron absorption by about 50 . When ionizable iron salts are given together with food the amount of iron absorbed is reduced.