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Despite being the most abundant metal on earth, iron is the most
prevalent single nutrient deficiency worldwide. The term newborn
possesses about 75 mg of elemental iron/kg (0.25–0.5
g of total body iron) and must absorb about 4.5 g of iron during
childhood, or about 1 mg/d, to achieve the nearly 5.0 g
of body iron in the average adult. An additional 0.2 to 0.5 mg/day of
absorbed iron is required to balance physiologic losses (eg, desquamation
of epithelial cells in the gastrointestinal tract). During periods
of maximal growth—infancy and adolescence—the
iron requirements for expanding blood volume and muscle mass may
exceed the rate of dietary iron accrual.
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Iron deficiency is the most common global nutritional deficiency with
an estimated 2 billion affected persons.1 Iron
deficiency affects all age groups, but is particularly common in
infants, young children, and women of childbearing age. Iron-deficiency
anemia is the most common hematologic disease of infancy and childhood.2
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In industrialized nations, the most common etiology of iron deficiency
is insufficient dietary iron. The availability of iron-fortified
formula, in conjunction with initiatives such as the US federal Special
Supplemental Nutrition Program for Women, Infants and Children (WIC)
and the American Academy of Pediatrics’ promotion of formula
in place of cow’s milk, have greatly reduced the prevalence
of iron deficiency in developed countries. According to the Fourth
National Health and Nutrition Examination Survey (NHANES-IV), iron
deficiency without anemia exists in 7% of toddlers ages
1 to 2 years, 9% of adolescent girls, and 16% of
women of childbearing age.3 Low income, minority
ethnicity, and poor maternal iron status are recognized socioeconomic
risk factors for iron-deficiency anemia.4-7 In
developing countries, the higher prevalence of iron-deficiency anemia
related to nutritional deficiency is compounded by the contribution
of chronic blood loss related to parasitic infections.
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Pathophysiology
and Genetics
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The majority of body iron is incorporated into the hemoglobin
of circulating erythrocytes and their marrow precursors. Only a
small fraction of the average daily requirement to support erythropoiesis
is absorbed from the diet. The majority of the daily erythroid iron requirement
is supplied by recovery of heme iron through the phagocytosis of
senescent erythrocytes by reticuloendothelial macrophages and degradation of
hemoglobin. This recycled iron is then made available to the developing
erythroid precursors in the bone marrow.
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Because only about 10% of dietary iron is absorbed,
the child’s diet must contain 10 to 15 mg of iron to maintain
a positive iron balance. During infancy, when only small amounts
of iron-rich foods may be consumed, this level of iron intake is
difficult to attain unless iron-fortified foods are provided. Infants
and children from low-income families continue to have iron deficiency,
despite a decline in the incidence of the condition over the past
30 years.
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Nonheme dietary iron, primarily in the ferric (Fe...