Chemistry Reference
In-Depth Information
Board: Institute of Medicine, 1997). In the United States, median phosphorus
intakes exceed DRIs for both genders by 300-600 mg/d. Furthermore, it is not
difficult for adults aged 19-70 yr to exceed the UL for phosphorus (4000 mg/
d). For example, consumption of certain high-energy bars and shakes or
creatinine monophosphate supplements at the manufacturer's recommended
daily dose alone will provide up to 3000 mg/d of phosphorus (Anderson et al.,
2006). In the United States, intakes of calcium are consistently lower than
those of phosphorus in the absence of calcium supplementation, the signifi-
cance of which remains controversial.
Infants, toddlers and adolescents derive 32-48% of their dietary phos-
phorus from milk and milk products, whereas dairy foods provide only
20-30% of phosphorus for most adult age and sex groups (Anderson et al.,
2006). Particular attention must be paid to increased risk of hyperphospha-
temia in neonates because renal handling of phosphorus is developmentally
immature in this age group. Persistent hyperphosphatemia during early
infancy may cause parathyroid hyperplasia, ectopic calcifications, low
serum calcitriol, and hypocalcaemia severe enough to induce neonatal tetany.
This condition is more prevalent in artificially fed than in breast-fed infants
(Food and Nutrition Board: Institute of Medicine, 1997) because bovine milk
or formulae may contain, respectively, six or three times as much phosphorus
as human milk (see Table 10.1). The phosphorylation level of caseins is
believed to have major implications for the formation of micelles that are
involved in delivering valuable calcium phosphate and other minerals to the
newborn (Kjeldsen et al., 2007). Even so, human milk with its low phos-
phorus content is both safer and better suited to the growth needs of the
infant than bovine milk. Casein micelle structure is not characterized fully,
but in all compositional models, micellar calcium phosphate is an integral
part of the casein micelle and is responsible for the structure and stability of
these particles. In bovine milk, about 54% of P
i
is soluble and about 46% is
associated with casein micelles as calcium phosphate, probably by binding
mainly to casein phosphoserine residues (organic phosphate) and glutamate
and aspartate residues (Gaucheron, 2005). In human milk, about 15% of
phosphorus occurs in an inorganic form, 23% is protein bound and about
62% is present with lipids (Renner, 1983).
10.5.
Magnesium
Magnesium is the most prevalent intracellular divalent cation and is needed
for enzymatic reactions vital to every metabolic pathway (Food and Nutri-
tion Board: Institute of Medicine, 1997; Committee on Minerals and Toxic
Substances in Diets and Water for Animals, 2005; Volpe, 2006). These
