Chemistry Reference
In-Depth Information
body, plasma potassium is a poor indicator of tissue concentrations. The
average concentration of potassium in mature human milk is 0.5 g/l, which is
considerably less than that of bovine milk (Food and Nutrition Board: Insti-
tute of Medicine, 2001). Lactating dairy cows have a very high dietary potas-
sium requirement (10 g/kg dry matter), and potassium is the mineral element
found in the highest concentration in milk (1.5 g/l) (Hunt and Meacham,
2001; Committee on Minerals and Toxic Substances in Diets and Water for
Animals, 2005). Potassium concentration in bovine colostrum is higher
than that in mature milk (Ontsouka et al., 2003). No relationship between
maternal dietary potassium and its concentration in milk has been demon-
strated. Almost all potassium in milk is absorbed from the digestive tract
(Flynn, 1992).
Bovine milk and dairy products can be major contributors to the total
dietary intake of potassium (24-29% in Ireland and the United Kingdom;
Flynn et al., 1990), because the richest sources, vegetables and fruits, often are
not consumed in recommended amounts. Potassium deficiency is unlikely
unless excessive alimentary (e.g., diarrhea) or renal (e.g., diuretic use) losses
occur because many foods contain significant amounts of potassium (Preuss,
2006). The dietary intake of potassium in the United States and Canada,
however, is considerably lower than the AI, which was based on the need to
blunt the severe salt sensitivity prevalent in African-American men, and
decreasing the risk of kidney stones (Food and Nutrition Board: Institute
of Medicine, 2001). A diet rich in fruits, vegetables and milk would assure a
healthy intake of potassium.
10.3.
Calcium
Calcium is the most abundant mineral in the body (
1000 g adults) (Favus
et al., 2006). Approximately 1% of total body calcium is found in extracellular
fluids, intracellular structures and cell membranes where it serves as a second
messenger, coupling intracellular responses to extracellular signals (Awumey
and Bukoski, 2006; Kirchhoff and Geibel, 2006). As such, calcium mediates
muscle contraction, nerve transmission and glandular secretion. The remain-
ing 99% of total body calcium is found in bones and teeth where its chemical
properties are indispensable for skeletal function and dental structure and
function.
Bone crystals (an analogue of the geological mineral, hydroxyapatite
[Ca
10
(PO
4
)
6
(OH)
2
]) have a significant (
39%) calcium content. These crys-
tals, with the ability to resist compression, are arrayed in a protein matrix that
has the ability to withstand tensile loads. Changes in either the inorganic (e.g.,
hydroxyapatite) or the organic (e.g., collagen) matrix components can alter
