Management of osteoporosis: is there a role for vitamin K?

Vitamin K is required for the biological activity of several coagulation factors, which is considered as the classical function of vitamin K. Recent research, however, suggests a role of vitamin K in bone metabolism. The metabolic role of vitamin K is to facilitate the carboxylation of glutamyl to gamma-carboxyglutamyl residues. Besides the hepatic tissue, in which the clotting factors are produced gamma-carboxyglutamyl-containing proteins are also abundantly available in bone tissue. Osteocalcin accounts for up to 80% of the total gamma-carboxyglutamyl content of mature bone. Human carboxylated osteocalcin contains 3 gamma-carboxyglutamyl residues which confer a highly specific affinity to the calcium ion of the hydroxyapatite molecule. Besides the gamma-carboxylation of osteocalcin vitamin K may also affect other parameters of bone metabolism, such as calcium hemostasis, and prostaglandin E2 and interleukin 6 production. Evidence from observational studies and first intervention trials indicate that vitamin K intakes much higher than the current recommendations improved biochemical markers of bone formation as well as bone density. In conclusion, the mechanistic data as well as the observational data and the results of the first controlled clinical trials in humans point to a beneficial effect of additional intakes of vitamin K in bone health.