There are 2 naturally occurring forms of it. Plants synthesize phylloquinone, known as vitamin K1. Bacteria synthesize a range of different K forms, using repeating 5-carbon units in the side chain of the molecule. These forms of vitamin K are designated menaquinone-n (MK-n), where n stands for the number of 5-carbon units. MK-n are collectively referred to as vitamin K2. MK-4 is not produced in significant amounts by bacteria, but appears to be synthesized by animals (including humans) from phylloquinone. MK-4 is found in a number of organs other than the liver at higher concentrations than phylloquinone. There may be a unique function of MK-4 that is yet discovered.

    Three vitamin-K dependent proteins have been isolated in bone. Osteocalcin is a protein synthesized by osteoblasts (bone forming cells). The synthesis of osteocalcin by osteoblasts is regulated by the active form of vitamin D, 1,25(OH)2D3 or calcitriol. The mineral-binding capacity of osteocalcin requires vitamin K-dependent gamma-carboxylation of three glutamic acid residues. The function of osteocalcin is thought to be related to bone mineralization. Matrix Gla protein (MGP) has been found in bone, cartilage, and soft tissue, including blood vessels. The results of animal studies suggest MGP prevents the calcification of soft tissue and cartilage, while facilitating normal bone growth and development. The vitamin K-dependent anticoagulant protein S is also synthesized by osteoblasts.

History:     The "K" is derived from the German word "koagulation". Phylloquinone (vitamin K1) and menaquinones (vitamins K2) are the major dietary forms of vitamin K.

Technicals:     The major function of the K vitamins is in the maintenance of normal levels of the blood clotting proteins, factors II, VII, IX, X and protein C and protein S, which are synthesized in the liver as inactive precursor proteins. Conversion from inactive to active clotting factor requires a posttranslational modification of specific glutamate (E) residues. This modification is a carboxylation and the enzyme responsible requires vitamin K as a cofactor. The resultant modified E residues are g-carboxyglutamate (gla). This process is most clearly understood for factor II, also called preprothrombin. Prothrombin is modified preprothrombin. The gla residues are effective calcium ion chelators. Upon chelation of calcium, prothrombin interacts with phospholipids in membranes and is proteolysed to thrombin through the action of activated factor X (Xa). During the carboxylation reaction reduced hydroquinone form of vitamin K is converted to a 2,3-epoxide form. The regeneration of the hydroquinone form requires an uncharacterized reductase. This latter reaction is the site of action of the dicumarol based anticoagulants such as warfarin.

Sources:     Kelp, alfalfa, green plants, leafy green vegetables, cow's milk, yogurt, egg yolks, blackstrap molasses, polyunsaturated oils, fish liver oils. Green leafy vegetables and some vegetable oils (soybean, cottonseed, canola, and olive) are all major contributors.

    Hydrogenation of vegetable oils may decrease the absorption and biological effect of dietary vitamin K

Signs or Symptoms of a Deficiency:   Naturally occurring vitamin K is absorbed from the intestines only in the presence of bile salts and other lipids through interaction with chylomicrons. Therefore, fat malabsorptive diseases can result in vitamin K deficiency. The synthetic vitamin K3 is water soluble and absorbed irrespective of the presence of intestinal lipids and bile. Since the vitamin K2 form is synthesized by intestinal bacteria, deficiency of the vitamin in adults is rare. However, long term antibiotic treatment can lead to deficiency in adults. The intestine of newborn infants is sterile, therefore, a deficiency in infants is possible if lacking from the early diet. The primary symptom of a deficiency in infants is a hemorrhagic syndrome.