Iron Deficiency : Part 3

by CDC

(Page 3 of 11)

Manifestations of Iron Deficiency

Iron deficiency is one of the most common nutritional deficiencies worldwide and has several causes. Iron deficiency represents a spectrum ranging from iron depletion, which causes no physiological impairments, to iron-deficiency anemia, which affects the functioning of several organ systems. In iron depletion, the amount of stored iron (e.g., as measured by serum ferritin concentration) is reduced but the amount of functional iron may not be affected. Persons who have iron depletion have no iron stores to mobilize if the body requires more iron. In iron-deficient erythropoiesis, stored iron is depleted and transport iron (e.g., as measured by transferrin saturation) is reduced further; the amount of iron absorbed is not sufficient to replace the amount lost or to provide the amount needed for growth and function. In this stage, the shortage of iron limits red blood cell production and results in increased erthryocyte protoporphyrin concentration. In iron-deficiency anemia, the most severe form of iron deficiency, the shortage of iron leads to underproduction of iron-containing functional compounds, including Hb. The red blood cells of persons who have iron-deficiency anemia are microcytic and hypochromic.

In infants (persons aged 0-12 months) and preschool children (persons aged 1-5 years), iron-deficiency anemia results in developmental delays and behavioral disturbances (e.g., decreased motor activity, social interaction, and attention to tasks). These developmental delays may persist past school age (i.e., 5 years) if the iron deficiency is not fully reversed. In these studies of development and behavior,

iron-deficiency anemia was defined as a Hb concentration of less than or equal to 10.0 g/dL or less than or equal to 10.5 g/dL; further study is needed to determine the effects of mild iron-deficiency anemia (for example, a Hb concentration of greater than 10.0 g/dL but less than 11.0 g/dL in children aged 1- less than 2 years) on infant and child development and behavior. Iron-deficiency anemia also contributes to lead poisoning in children by increasing the gastrointestinal tract's ability to absorb heavy metals, including lead. Iron-deficiency anemia is associated with conditions that may independently affect infant and child development (e.g., low birthweight, generalized undernutrition, poverty, and high blood level of lead) that need to be taken into account when interventions addressing iron-deficiency anemia are developed and evaluated.

In adults (persons aged greater than or equal to 18 years), iron-deficiency anemia among laborers (e.g., tea pickers, latex tappers, and cotton mill workers) in the developing world impairs work capacity; the impairment appears to be at least partially reversible with iron treatment. It is not known whether iron-deficiency anemia affects the capacity to perform less physically demanding labor that is dependent on sustained cognitive or coordinated motor function.

Among pregnant women, iron-deficiency anemia during the first two trimesters of pregnancy is associated with a twofold increased risk for preterm delivery and a threefold increased risk for delivering a low-birthweight baby. Evidence from randomized control trials indicates that iron supplementation decreases the incidence of iron-deficiency anemia during pregnancy, but trials of the effect of universal iron supplementation during pregnancy on adverse maternal and infant outcomes are inconclusive.

Risk for and Prevalence of Iron Deficiency in the United States

A rapid rate of growth coincident with frequently inadequate intake of dietary iron places children aged less than 24 months, particularly those aged 9-18 months, at the highest risk of any age group for iron deficiency. The iron stores of full-term infants can meet an infant's iron requirements until ages 4-6 months, and iron-deficiency anemia generally does not occur until approximately age 9 months. Compared with full-term infants of normal or high birthweight, preterm and low-birthweight infants are born with lower iron stores and grow faster during infancy; consequently, their iron stores are often depleted by ages 2-3 months and they are at greater risk for iron deficiency than are full-term infants of normal or high birthweight. Data from the third National Health and Nutrition Examination Survey (NHANES III), which was conducted during 1988-1994, indicated that 9% of children aged 12-36 months in the United States had iron deficiency (on the basis of two of three abnormal values for erythrocyte protoporphyrin concentration, serum ferritin concentration, and transferrin saturation) and that 3% also had iron-deficiency anemia. The prevalence of iron deficiency is higher among children living at or below the poverty level than among those living above the poverty level and higher among black or Mexican-American children than among white children.

Evidence from the Continuing Survey of Food Intakes by Individuals (CSFII), which was conducted during 1994-1996, suggests that most infants meet the recommended dietary allowance for iron through diet (Table 5; these data exclude breast-fed infants). However, the evidence also suggests that more than half of children aged 1-2 years may not be meeting the recommended dietary allowance for iron through their diet.

An infant's diet is a reasonable predictor of iron status in late infancy and early childhood. For example, approximately 20%-40% of infants fed only non-iron-fortified formula or whole cow's milk and 15%-25% of breast-fed infants are at risk for iron deficiency by ages 9-12 months. Infants fed mainly iron-fortified formula (greater than or equal to 1.0 mg iron/100 kcal formula) are not likely to have iron deficiency at age 9 months. Another study has documented that intake of iron-fortified cereal protects against iron deficiency: among exclusively breast-fed infants who were fed cereal starting at age 4 months, 3% of infants who were randomized to receive iron-fortified cereal compared with 15% of infants who were randomized to receive non-iron-fortified cereal had iron-deficiency anemia at age 8 months. The effect of prolonged exclusive breast feeding on iron status is not well understood. One nonrandomized study with a small cohort suggested that exclusive breast feeding for greater than 7 months is protective against iron deficiency compared with breast feeding plus the introduction of non-iron-fortified foods at age less than or equal to 7 months; infants weaned to iron-fortified foods were not included in this study.

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