Commentaries

Boning up on vitamin K The nature and significance of the relationship between vitamin K status and bone health has been debated for some years. Vitamin K is required for the gamma carboxy-lation of glutamic acid residues in three bone proteins, namely osteocalcin, matrix Gla protein, and protein S. Although the roles of these proteins have not been clearly defined, there is evidence that osteocalcin, which is produced by cells of the osteocyte/osteoblast lineage and has three vitamin K dependent gamma carboxyglutamic acid (Gla) residues, may be involved in the mineralisation of bone matrix1; in addition, it may function as a negative regulator of bone formation, deletion of the osteocalcin gene in mice resulting in increased bone mass.2 Approxi-mately 30 % of synthesised osteocalcin is released into th