Chemistry Reference
In-Depth Information
are decreasing. This results in plasma or serum magnesium being a poor
indicator of tissue magnesium status. The concentration of magnesium in
human colostrum is about 30% higher than in mature human milk (Raja-
lakshmi and Srikantia, 1980), which is about 34 mg (1.4 mmol)/l (Food and
Nutrition Board: Institute of Medicine, 1997; Hunt et al., 2005). Mature
bovine milk contains about 100 mg (4.1 mmol)/l (Hunt and Meacham,
2001; Volpe, 2006). Magnesium concentration in bovine colostrum is two to
three times that in mature milk, but decreases to the mature milk value within
the first 1-3 d of lactation (Hidiroglou and Proulx, 1982). The concentration
of magnesium in human milk increases slightly between months 1 and 4
(Hunt et al., 2005) but remains relatively constant in bovine mature milk
(Hidiroglou and Proulx, 1982) over the first year of lactation. Milk magne-
sium concentration is unaffected by dietary magnesium intake. Because
bovine milk contains over three times as much magnesium as human milk,
commercial formulae that are based on bovine milks are generally higher in
magnesium concentration (40-50 mg or 1.7-2.1 mmol/l) than human milk
(Food and Nutrition Board: Institute of Medicine, 1997).
In human milk, 2% of magnesium is in the fat fraction, 6% in casein,
36% associated with whey proteins and 58% as low-molecular-weight forms
(Fransson and Lonnerdal, 1983). In bovine milk, 98-100% of the magnesium
is in the skim milk phase (Fransson and Lonnerdal, 1983), with 65% in a
soluble form (40% as magnesium citrate, 7% as magnesium phosphate, and
16% as free magnesium ions). The other 35% of magnesium is colloidal and
associated with casein micelles (Holt, 1985). Premature and full-term infants
absorb 45% of the magnesium in human milk (Food and Nutrition Board:
Institute of Medicine, 1997) and absorption varies from 40 to 71% in bovine
milk-based infant formulae (Food and Nutrition Board: Institute of Medi-
cine, 1997).
Green leafy vegetables, whole grains and nuts are the richest sources of
magnesium (Volpe, 2006). However, because milk and milk products are
moderate sources of magnesium, increasing their intake would be a reason-
able recommendation for assuring a healthy intake of this element.
10.6.
Iron
Dietary iron is required for a wide variety of biochemical processes. Biologi-
cal systems utilize the chemical reactivity of iron and interconvert iron
oxidation states. This interconversion allows iron to participate in electron
transfer as well as the reversible binding to ligands (Food and Nutrition
Board: Institute of Medicine, 2001). Iron is suited to participate in oxygen
transport and storage, electron transfer and substrate oxidation-reduction.
