Chemistry Reference
In-Depth Information
high proportion of newly synthesized osteocalcin is incorporated into
bone, approximately 30% of it is released into the circulation and serum
levels of the protein are used widely as an indicator of the rate of bone
formation (Brown et al., 1984). The precise physiologic function of osteo-
calcin remains unclear. The less well characterized GMP has a molecular
mass of 9600 Da and contains 5 Gla residues and in contrast to osteo-
calcin, which is exclusively associated to mineralized tissues, MGP is
present in cartilage and is expressed at a high rate in many soft tissues
(heart, kidney, lungs), in addition to bone (Fraser et al., 1988).
12.5.5.
Vitamin K Deficiency and Chronic Disease
Newborn infants are at serious risk of haemorrhaging because of
poor placental transfer of vitamin K, lack of intestinal bacteria and the
low vitamin K content in breast milk. For this reason, they receive intra-
muscular vitamin K at birth. In children and adults, 'clinical' vitamin K
deficiency in terms of blood coagulation is rare. However, 'subclinical'
vitamin K deficiency in extrahepatic tissues, particularly in bone, is not
uncommon in the adult population. The multitude of proteins which
require carboxylation of Glu to Gla residues for proper functioning sug-
gests that poor vitamin K status may contribute to certain chronic vascular
and skeletal diseases. For example, post-menopausal loss of bone mass is
associated with a long-lasting poor vitamin K status and may contribute to
osteoporosis (Weber, 2001). Furthermore, it has been reported that bone
mineral density is lower and fracture rates higher among patients with
lower circulating vitamin K levels (Kanai et al., 1997). In two prospective
cohorts, women with low-dietary vitamin K levels appear to be at increased
risk of hip fracture (Feskanich et al., 1999; Booth et al., 2000). Increasing
evidence is emerging, suggesting a role for vitamin K in the calcification of
arteries and atherogenesis (Kaneki et al., 2006). Moreover, the therapeutic
potential of vitamin K
2
as an antihepatoma drug has been recently high-
lighted (for review see Kaneki et al., 2006).
12.5.6.
Vitamin K in Milk
Milk is not a good dietary source of vitamin K, containing between
3.5-18 mg/l as phylloquinone (Haroon et al., 1982) and contributes minimally
to vitamin K intake in adults (Booth et al., 1996). Mature human milk
contains less phylloquinone than cow's milk (
0.25 mg/l) (Haroon et al.,
1982). However, vitamin K levels are higher in colostrum than in mature
milk (von Kries et al., 1987). The menaquinone concentration in human milk
has not been accurately determined but appears to be much lower than that of
