Vitamin K and bone health.

[Guest guest]

Vitamin K and bone health.

Bugel S.

Department of Human Nutrition, The Royal Veterinary and Agricultural

University, Rolighedsvej 30, 1958 Frederiksberg C, Denmark. shb@...

Vitamin K, originally recognised as a factor required for normal blood

coagulation, is now receiving more attention in relation to its role in bone

metabolism. Vitamin K is a coenzyme for glutamate carboxylase, which

mediates the conversion of glutamate to gamma-carboxyglutamate (Gla). Gla

residues attract Ca2+ and incorporate these ions into the hydroxyapatite

crystals. There are at least three Gla proteins associated with bone tissue,

of which osteocalcin is the most abundant and best known. Osteocalcin is the

major non-collagenous protein incorporated in bone matrix during bone

formation. However, approximately 30% of the newly-produced osteocalcin

stays in the circulation where it may be used as an indicator of bone

formation. Vitamin K deficiency results in an increase in undercarboxylated

osteocalcin, a protein with low biological activity. Several studies have

demonstrated that low dietary vitamin K intake is associated with low bone

mineral density or increased fractures. Additionally, vitamin K

supplementation has been shown to reduce undercarboxylated osteocalcin and

improve the bone turnover profile. Some studies have indicated that high

levels of undercarboxylated osteocalcin (as a result of low vitamin K

intake?) are associated with low bone mineral density and increased hip

fracture. The current dietary recommendation for vitamin K is 1 microg/kg

body weight per d, based on saturation of the coagulation system. The daily

dietary vitamin K intake is estimated to be in the range 124-375 microg/d in

a European population. Thus, a deficiency based on the hepatic coagulation

system would be unusual, but recent data suggest that the requirement in

relation to bone health might be higher.

PMID: 15018483 [PubMed - in process]

------------------------------------------------------------------------