Chemistry Reference
In-Depth Information
stable (Kirksey et al., 1979; Lonnerdal, 1997), exhibits a transient decrease
(Friel et al., 1999), or decreases slightly but significantly (Hunt et al., 2005)
during the first 4 months of lactation. Generally, the maternal diet is not
believed to affect the concentration of calcium in breast milk (Lonnerdal,
1986). However, there is some evidence that calcium levels in breast milk are
lower than normal during extended lactation (Laskey et al., 1990) and that
breast milk of lactating young teenage mothers may have lower calcium
concentrations than that of older women (Lipsman et al., 1985). The cal-
cium content of human milk is considerably lower than that of bovine milk
(
1100 mg/l) (Table 10.1) and also that of milk-based (
500 mg/l) (Hunt
and Meacham, 2001) or soy-based (
600 mg/l) formulae. Because formula-
fed infants usually consume higher volumes than breast-fed infants, they
receive at least twice the amount of calcium that breast-fed infants ingest
(Lonnerdal, 1997). The fundamental concept that the body composition of
exclusively breast-fed infants in the first 6 months of life is the ideal standard
for all full-term infants is now in conflict with the reality that it is techno-
logically possible with infant formulae to increase calcium absorption and
bone calcium accretion to levels above those achieved by human milk-fed,
full-term infants. However, there are no data to support such a goal or
suggest that it is beneficial for short- or long-term bone health (Abrams,
2006). Regardless, in the United States, the mandate of the Infant Formula
Act and certain policy statements have led to the marketing of infant
formulae with much higher concentrations of calcium than is present in
human milk (Abrams, 2006).
Calcium sources should be evaluated on the basis of both content and
bioavailability of calcium (Weaver et al., 1999). About 60-70% of calcium is
absorbed from human milk, leading to a net retention of about 90-100 mg
calcium per day during the first 6 months for babies fed exclusively human
milk (Abrams, 2006). Calcium absorption from bovine milk (
32%) is similar
to that from other dairy products even though the lactose content and the
chemical form of calcium in cheese or yogurt are altered during processing
(Weaver et al., 1999). Fractional calcium absorption from infant formulae
tends to range between 40 and 60% in most studies (Abrams, 2006). Calcium
salts, regardless of solubility, have fractional calcium absorption values
similar to that for bovine milk, with the exception of calcium citrate malate,
from which absorption is slightly higher (Weaver et al., 1999). Fractional
absorption of calcium from low-oxalate vegetables, i.e., broccoli (61%), bok
choy (54%) or kale (49%) is actually higher than that from bovine milk
(Weaver et al., 1999). Calcium bioavailability is typically greatly reduced in
foods containing high level of oxalate and/or phytate (e.g., common dried
beans) but foods produced from soybeans, rich in both oxalate and phytate,
have relatively high calcium bioavailability. However, increasing dietary
