Vitamin K is a group of structurally similar, fat-soluble vitamins that the human body needs for post translational modification of certain proteins required for blood coagulation, and in metabolic pathways in bone and other tissue.
The primary function of vitamin K is to aid in the formation of clotting factors and bone proteins. It serves as a cofactor in the production of six proteins that regulate blood clotting, including prothrombin. In addition, it helps to form osteocalcin, a protein necessary for the mineralization of bone. Vitamin K also aids in the formation of glucose into glycogen for storage in the liver. In addition, it promotes the prevention and reversal of arterial calcification, plague progression and lipid peroxidation. Deficiency may increase the risk of calcification of arterial walls, particularly in individuals on vitamin D supplementation (Vitamin D promotes calcium absorption). Vitamin K exists in three forms: K1, a natural form found in plants (phylloquinone); K2, which is synthesized in the intestine (menaquinone); and K3, a synthetic form that must be activated in the liver (menadione). Vitamin K is absorbed in the upper small intestines and transported throughout the body in chylomicrons.
Excessive bleeding, a history of bruising, appearance of ruptured capillaries or menorrhagia (heavy periods) are the most common clinical symptoms of overt vitamin K deficiency, although subclinical deficiency may not affect clotting mechanisms.
Due to its critical role in bone formation, long-term vitamin K deficiency may impair bone integrity and growth, eventually predisposing a person to osteoporosis. Antibiotic usage can induce vitamin K deficiency since it upsets the balance of normal intestinal flora. Anticoagulants such as Coumadin and warfarin can also deplete vitamin K by blocking the activation of prothrombin. However, patients on warfarin or other blood anticoagulants should not supplement with vitamin K unless specifically recommended and approved by their physician. Other causes of deficiency include celiac disease, liver disease, certain medications (i.e. aspirin, Dilantin), very high doses of vitamins A and E (over 600 IU) and gastrointestinal disorders associated with the malabsorption of fats, such as bile duct obstruction, pancreatitis or inflammatory bowel disease.