Vitamin K plays an important role in blood clotting and bone metabolism (carboxylation of osteocalcin). High serum concentrations of undercarboxylated osteocalcin and low serum concentrations of vitamin K are associated with lower bone mineral density and increased risk of hip fracture. Vitamin K supplements may improve bone mass in postmenopausal women. Vitamin K prevents calcification of arteries and other soft tissue. Calcification of organs and other soft tissue is an adverse consequence of aging. Vitamin K may play a role in the regulation of blood sugar. The pancreas, which makes insulin, has the second highest amount of vitamin K in the body.

Vitamin K and blood clotting - Vitamin K's primary function is to regulate normal blood clotting (due to its role in the synthesis of prothrombin). Blood clotting is a process that begins automatically when any injury produces a tear in a blood vessel. The process of blood clotting involves a collection of molecules, which circulate continuously through the bloodstream. Vitamin K regulates normal blood clotting by helping the body transport calcium. Protein Z appears to enhance the action of thrombin (the activated form of prothrombin) by promoting its association with phospholipids in cell membranes. Protein C and protein S are anticoagulant proteins that provide control and balance in the coagulation cascade. Vitamin K2, not vitamin K1 (phylloquinone; phytonadione), may improve a group of blood disorders known as myelodysplastic syndromes.

Vitamin K and bone health - Vitamin K supplements improve bone health and reduce risk of bone fractures, particularly in postmenopausal women who are at risk for osteoporosis. Three vitamin-K dependent proteins have been isolated in bone. Higher vitamin K levels correspond to greater bone density, while low levels of vitamin K have been found in those with osteoporosis. In bones, vitamin K mediates the gamma-carboxylation of glutamyl residues on several bone proteins, notably osteocalcin. Osteocalcin is a protein synthesized by osteoblasts (bone forming cells). The mineral-binding capacity of osteocalcin requires vitamin K-dependent gamma-carboxylation of three glutamic acid residues.

Vitamin K and liver diseases - Vitamin K is used to reduce risk of bleeding in liver disease, jaundice, malabsorption, or in association with long-term use of aspirin or antibiotics. Gastrointestinal problems that decrease the absorption of vitamin K, such as obstructions in the bile duct, cystic fibrosis, sprue, Crohn's disease, colitis and medications that reduce the absorption of this vitamin, such as antibiotics. Vitamin K deficiency in those with cystic fibrosis is worsened by their recurrent need for antibiotics. Vitamin K has been used in the treatment of heavy menstrual bleeding, and with vitamin C to treat morning sickness. Newborns are at risk for bleeding in the brain because of the trauma of coming through the birth canal during delivery.