Dietary Iron exists as heme iron, found in hemoglobin, myoglobin, and some enzymes; and as nonheme iron, found predominantly in plant foods, but also in some animal foods as nonheme enzymes and ferritin. From 2% to 10% of nonheme iron in vegetables is absorbed, and from 10% to 30% of iron heme and nonheme from animal sources is typically absorbed.
Several factors affect the intestinal absorption of iron. The efficiency of iron absorption is determined to some extent by the foods from which it is derived or with which it is consumed. Ascorbic acid, the most potent enhancer of iron absorption, reduces ferric to ferrous iron and forms a chelate with iron that remains soluble at the alkaline pH of the lower small intestine. The degree of gastric acidity enhances solubility and therefore bioavailability of iron derived from foods.
Certain physiologic states such as pregnancy and growth that involve increased blood formation stimulate iron absorption. In addition, more iron is absorbed during iron deficiency states because of adaptive mechanisms that enhance nonheme iron absorption. Oxalates can inhibit absorption. Tannins, which are polyphenols, in tea also reduce nonheme iron absorption.
Iron metabolism is complex because this element is involved in so many aspects of life, including red blood cell function, myoglobin activity, and the roles of numerous heme and nonheme enzymes. Because of its oxidation-reduction (redox) properties, iron has a role in the blood and respiratory transport of oxygen and carbon dioxide, and it is an active component of the cytochromes (enzymes) involved in the processes of cellular respiration and energy) ATP) generation. Iron is also involved in immune function and cognitive performance; this underscores the importance of preventing iron deficiency anemia throughout the world.
Food Sources and Intakes
By far the best source of dietary iron is liver, followed by seafood, kidney, heart, lean meat, and poultry. Dried beans and vegetables are the best plant sources. Some other foods that provide iron are egg yolks, dried fruits, dark molasses, wholegrain and enriched breads, wine, and cereal. Old-fashioned iron skillets used for cooking add to the total iron intake.
Iron deficiency, the precursor of iron deficiency anemia, is the most common of all nutritional deficiency diseases. In the United States and worldwide, iron deficiency anemia is prevalent among children and women of childbearing age.
Infants and young children: 711mg/day, depending on age
Older children and adolescents: 815 mg/day, depending on age
Asults: 818mg/day, depending on age and gender
Pregnant: 27 mg/day
Lactating: 910 mg/day, depending on age