Chemistry Reference
In-Depth Information
Several other mineral elements (aluminum, bromine, cadmium, cesium,
lead, lithium, strontium, mercury, silver, rubidium and tin) are present nor-
mally in very low amounts in bovine and human milks. They are considered
important because of their high orders of toxicity but are not reviewed here
because of the lack of compelling evidence for their beneficial functions. All
essential or beneficial minerals are toxic when ingested in excess. Therefore,
an upper limit (UL) of intake has been established for each (Table 10.2).
Because individual ULs are generally well above the total amounts supplied
by typical diets, the toxicological aspects of each mineral are discussed only
when they are considered relevant.
Human milk and bovine milk are markedly different in several aspects,
including mineral content (Table 10.1). Furthermore, the bioavailability of
most minerals in human milk is much higher than from bovine milk or infant
formula (Emmett and Rogers, 1997). Frequent revision of humanized infant
formulae to match the nutritive value of human milk complicates compar-
isons and notable current differences in content or bioavailability are identi-
fied in the discussion. This discussion focuses on mature human milk which
has a mineral content considerably different from that of early and transi-
tional human milks. In human milk, the concentrations of most minerals
remain fairly constant throughout the course of lactation. Notable exceptions
are zinc, copper and iron, but even these elements have predictable patterns of
change over time, falling for several months after parturition (Emmett and
Rogers, 1997).
Mineral concentrations in human milk are resistant to changes in
maternal dietary mineral intakes (except for selenium; Kumpulainen et al.,
1985), age, parity or lactational history (Butte et al., 1987). Differences in
mineral composition of milk between term and preterm mothers are not
universal and the lack of agreement among investigators may be due to
differences in sample collection, a wide range of gestational ages and greater
individual variation in the composition of milk from mothers of premature
infants (Friel et al., 1999). Reported values for the concentration of a given
mineral in milk among laboratories are remarkably consistent (Table 10.1).
Although each mineral is discussed separately, interactions of minerals with
each other, with other constituents of milk and with other food constituents
are considered to be of paramount importance.
10.2.
Sodium, Chloride and Potassium
The cation sodium and the anion chloride are required to maintain extra-
cellular volume and plasma osmolarity. Human populations have the capacity
to survive at extremes of sodium intake from less than 0.2 g (10 mmol)/d by the
