Chemistry Reference
In-Depth Information
Debate continues as to whether the iron content of human milk is
sufficient for the breast-fed infant and whether these infants should be supple-
mented with iron. The concentration of iron in human milk is normally very
low and decreases significantly further during the first 12 weeks of lactation
(Butte et al., 1987; Davidsson et al., 1994; Hunt et al., 2004; Kelleher and
Lonnerdal, 2005). Even so, several studies have demonstrated that the iron
status of exclusively breast-fed infants is satisfactory up to 6 months of age and,
in some studies, up to 9 or 12 months of age (Lonnerdal, 1997). A panel of
experts (American Academy of Pediatrics, 2005) concluded that exclusive
breast-feeding is sufficient to support optimal growth and development for
approximately the first 6 months of life but complementary foods rich in iron
should be introduced gradually beginning around 6 months of age. Preterm
and low-birth-weight infants have high iron requirements (Griffin and
Abrams, 2001). More recently, a report suggested that iron supplementation
from 1 to 6 months of age results in higher hemoglobin and mean corpuscular
volume at 6 months of age and significantly higher visual acuity and psycho-
motor developmental indices at 13 months of age (Friel et al., 2003). On the
other hand, new evidence (Sazawal et al., 2006) suggests that current guidelines
for universal supplementation with iron and folic acid in areas of high malaria
transmission should be revised. Children in those areas who received iron and
folic acid were more likely to die or need treatment in hospital for an adverse
event. In general, iron-deficient and anemic children can benefit from supple-
mentation but supplementation of those who are not iron deficient might be
harmful.
Earlier estimates (Lonnerdal, 1989) of typical iron absorption from human
milk (50%) are considerably higher than newer estimates (
20%) obtained with
stable isotope technology (Fomon et al., 1993; Lonnerdal, 1997). Also, formula-
fed infants absorb considerably less iron (
7%) than breast-fed infants (Fomon
et al., 1993). Reasons for the higher bioavailability of iron in human milk are not
understood. Lactoferrin is a highly efficient mammalian iron-scavenging defense
protein (
80 kDa) (Weinberg, 2007), a glycoprotein that has a very high
association constant for iron (K
a
,1.0
10
30
M
-1
) (Lonnerdal, 1997) and is
found at high concentrations in all human milk, including colostrum (
9.8 g/l)
and mature breast milk (
2.4 g/l) (Velona et al., 1999). Despite a very high
binding affinity, there is still no good evidence that lactoferrin plays any role as
an iron transporter or is involved in ''mainstream'' iron metabolism (Brock,
2002). In fact, in the murine model, lactoferrin ablation did not result in iron-
deficiency anemia (Ward and Conneely, 2004) and, in infants older than
4 months of age, iron absorption was found to be slightly higher from lactofer-
rin-free milk than from intact breast milk (Lonnerdal, 1997).
Human milk, as well as bovine milk and milk products, are poor sources
of iron (Table 10.1) (Pennington et al., 1987). To prevent iron deficiency and
