more sensitive to iron depletion. Approximately 73 percent of the body's iron is normally incorporated into hemoglobin and 12 percent in the storage complexes ferritin and hemosiderin. A very important 15 percent, however, is incorporated into a variety of other iron-containing compounds essential to cell function.
WHO data indicate global rates for iron deficiency anemia in developing countries of 51 percent for children 0—4 years of age, 46 percent for school-age children, 42 percent for women, and 26 percent for men (NSS1) (see Table 3-1 for the WHO diagnostic criteria for iron-deficiency anemia). Even in the United States, the NHANES II survey found an overall 7 percent prevalence of actual anemia in women 15–44 years of age, but with the highest burden in minority and poverty groups (WHO/UNICEF/UNU, in press).
In the absence of pathological iron losses, iron requirements are greatest during periods of growth (e.g., childhood); pregnancy; and, in women of reproductive age, because of menstruation. Documented associations between iron deficiency and ferropenic anemia include smaller babies, higher rates of stillbirth and perinatal mortality, more premature deliveries, and newborns with lower iron stores. An infant's risk of developing iron deficiency begins in utero, because premature delivery deprives the baby of the accumulation of iron near the end of pregnancy and smaller babies generally have less body iron (Widowson and Spray, 1951; Rosso, 1990). Unfortunately, the iron in breast milk cannot prevent the exhaustion of iron reserves in the first 4–6 months brought about by rapid growth. Poor weaning practices and inadequate feeding during childhood contribute further to the persistence or development of iron deficiency. When growth rates diminish, risk of iron deficiency is reduced unless there is abnormal blood loss to parasitic infection; menstruating women, however, continue to be at risk. In this group, about 20 percent have skewed menstrual blood (iron) losses in the upper ranges of the normal distribution that cannot be covered by their usual dietary intake, and over 50 percent have inadequate or depleted prepregnancy iron reserves (Cook et al., 1986; Custer et al., 1995; Franzetti et al., 1984; Hallberg and Rossander-Hulten, 1991). Because of the high iron requirements of pregnancy, iron deficiency is the rule, particularly in teenage gestations and in women with frequent pregnancies.
The stages in the development of iron deficiency are the depletion of iron stores, as indicated by low plasma ferritin; interference with biochemical processes, indicated by low transferrin saturation and elevated free erythrocyte protoporphyrin and serum transferrin receptors; and, finally, anemia, as indicated by low hemoglobin. It should be noted that although transferrin receptors appear promising as an indicator, standard cutoffs and interpretation of values from different commercial assays are yet to be developed. Up to an anemia prevalence