DƯỢC LÍ Goodman & Gilman's The Pharmacological Basis of Therapeutics 12th, 2010

1080
SECTION IV
INFLAMMATION. IMMUNOMODULATION, AND HEMATOPOIESIS
Table 37–4
Daily Iron Intake and Absorption
IRON REQUIREMENT AVAILABLE IRON (mg/kg) SAFETY FACTOR
SUBJECT (mg/kg) POOR DIET–GOOD DIET AVAILABLE/REQUIREMENT
Infant 67 33–66 0.5–1
Child 22 48–96 2–4
Adolescent (male) 21 30–60 1.5–3
Adolescent (female) 20 30–60 1.5–3
Adult (male) 13 26–52 2–4
Adult (female) 21 18–36 1–2
Mid-to-late pregnancy 80 18–36 0.22–0.45
risk, whereas iron balance in adult men and nonmenstruating
women is reasonably secure. The difference between dietary supply
and requirements is reflected in the size of iron stores, which are
low or absent when iron balance is precarious and high when iron
balance is favorable (Table 37–2). Thus in infants after the third
month of life and in pregnant women after the first trimester, stores
of iron are negligible. Menstruating women have approximately
one-third the stored iron found in adult men, indicative of the extent
to which the additional average daily loss of ~0.5 mg of iron
affects iron balance.
Iron Deficiency. Iron deficiency is the most common
nutritional disorder (McLean et al., 2009). The prevalence
of iron-deficiency anemia in the U.S. is on the
order of 1-4% and depends on the economic status of
the population. In developing countries, up to 20-40%
Absorption of
nonheme iron (%)
20 0 mg
15
10
5
0
Low Medium High
Availability of nonheme iron
250 mg
500 mg
1000 mg
Figure 37–4. Effect of iron status on the absorption of nonheme
iron in food. The percentages of iron absorbed from diets of low,
medium, and high bioavailability in individuals with iron stores
of 0, 250, 500, and 1000 mg are portrayed. (After Monsen et al.,
1978; reproduced with permission by the American Journal of
Clinical Nutrition. © Am J Clin Nutr. American Society for
Clinical Nutrition.)
of infants and pregnant women may be affected. Better
iron balance has resulted from the practice of fortifying
flour, the use of iron-fortified formulas for infants,
and the prescription of medicinal iron supplements during
pregnancy.
Iron-deficiency anemia results from dietary
intake of iron that is inadequate to meet normal
requirements (nutritional iron deficiency), blood loss,
or interference with iron absorption (Clark, 2009).
This can have a genetic basis, as in iron-refractory iron
deficiency anemia in which patients have iron deficiency
that is unresponsive to oral iron, but partially
responsive to parenteral iron (Finberg, 2009). Poor
oral absorption also can be acquired, as in conditions
associated with impaired oral absorption of vitamin
B 12
(Fernandez-Banares et al., 2009), or following
partial gastrectomy. More severe iron deficiency is
usually the result of blood loss, either from the GI
tract, or in women, from the uterus. Finally, treatment
of patients with erythropoietin can result in a functional
iron deficiency.
Iron deficiency in infants and young children can
lead to behavioral disturbances and can impair development,
which may not be fully reversible. Iron deficiency
in children also can lead to an increased risk of lead
toxicity secondary to pica and an increased absorption
of heavy metals. Premature and low-birthweight infants
are at greatest risk for developing iron deficiency, especially
if they are not breast-fed and/or do not receive
iron-fortified formula. After the age of 2-3 years, the
requirement for iron declines until adolescence when
rapid growth combined with irregular dietary habits
again increases the risk of iron deficiency. Adolescent
girls are at greatest risk; the dietary iron intake of
most girls ages 11-18 is insufficient to meet their
requirements.