**2.1 Epidemiology of iron deficiency in children**

Iron deficiency and iron deficiency anemia affect a large proportion of people worldwide (Beard & Stoltzfus, 2001; Benoit 2001; Stoltzfus, 2001). According to the Fourth National Health and Nutrition Examination Survey (NHANES IV), iron deficiency without anemia exists in 7% of toddlers aged 1 to 2 years, 9% of adolescent girls, and 16% of women of childbearing age, (Looker, 2002) a true public health concern. Unfortunately, studies of the prevalence of iron deficiency anemia use arbitrary definitions of anemia and iron deficiency, such as a hemoglobin less than 11 (Eden & Mir, 1997). There is often no attempt to separate iron deficiency based on severity, so that the true incidence of *severe* iron deficiency anemia is unknown.

It must be remembered that iron deficiency and iron deficiency anemia are somewhat distinct, but overlapping and related disorders. Although confirmatory studies are lacking, it is probably true that the greatest cause of iron deficiency worldwide and in the United States is nutrition, i.e. lack of sufficient iron in the diet, and the greatest cause of iron deficiency *anemia* worldwide and in the United States is slow gastrointestinal bleeding. Statistics stating the leading causes of these conditions can easily mislead the practitioner, since the epidemiology of iron deficiency and iron deficiency are different, and also varies by age, gender, socioeconomic status and geography. Worldwide, and especially in poor countries, infestation by hookworm (mostly Necator americanus and Ancylostoma duodenale) is the leading cause of gastrointestinal blood loss leading to iron deficiency and iron deficiency anemia. Infestation by Trichuris trichiura, the cause of trichuriasis (whipworm) infection is common throughout many parts of the world, and symptomatic infestations leading to iron deficiency or growth retardation preferentially affect children between 2 and 10 years of age. By contrast, in the United States, parasitic infestation has become distinctly rare due to improved sanitation and the fact that most children in the U.S. now wear shoes when outdoors. In the United States, cultural differences in feeding practices affect the incidence of iron deficiency anemia (Kwiatowski, 1999)

#### **2.2 Health effects of iron deficiency**

The association between iron deficiency anemia and impaired neurocognitive function is well established, and is independent of psychosocial and environmental factors. The association is especially strong in young children and infants (Oski, 1979). There is evidence that iron deficiency that has not progressed to anemia is also associated with poor neurocognitive function (Akman et al., 2004; Cook & Lynch 1986; Grantham-McGregor & Ani, 2001; Oski, 1983, 1985; Pollitt et al., 1986). Many possible mechanisms for the association have been suggested and investigated, but the true etiology is unknown (Beard, 2001; Erikson et al., 2001; Ortiz et al., 2004). Whether and to what extent this poor neurocognitive function can be reversed by correcting the deficiency is debated (Akman et al, 2004; Lozoff et al., 1982, 1996, 2000; Oski, 1983; Walter et al., 1989)

Many types of anemia such as hemoglobinopathies, hemolytic anemias and iron deficiency lead to increased absorption of both iron and lead from the GI tract. Coupled with the increased incidence of pica in these anemias, one effect of anemia, including that due to iron deficiency, is the increased incidence of lead poisoning and its health effects.
