<P> Vitamin K is a group of structurally similar, fat - soluble vitamins that the human body requires for complete synthesis of certain proteins that are prerequisites for blood coagulation (K from Koagulation, Danish for "coagulation") and which the body also needs for controlling binding of calcium in bones and other tissues . The vitamin K - related modification of the proteins allows them to bind calcium ions, which they cannot do otherwise . Without vitamin K, blood coagulation is seriously impaired, and uncontrolled bleeding occurs . Preliminary clinical research indicates that deficiency of vitamin K may weaken bones, potentially leading to osteoporosis, and may promote calcification of arteries and other soft tissues . </P> <P> Chemically, the vitamin K family comprises 2 - methyl - 1, 4 - naphthoquinone (3 -) derivatives . Vitamin K includes two natural vitamers: vitamin K and vitamin K. Vitamin K, in turn, consists of a number of related chemical subtypes, with differing lengths of carbon side chains made of isoprenoid groups of atoms . </P> <P> Vitamin K, also known as phylloquinone, is made by plants, and is found in highest amounts in green leafy vegetables because it is directly involved in photosynthesis . It may be thought of as the plant form of vitamin K. It is active as a vitamin in animals and performs the classic functions of vitamin K, including its activity in the production of blood - clotting proteins . Animals may also convert it to vitamin K . </P> <P> Bacteria in the gut flora can also convert K into vitamin K (menaquinone). In addition, bacteria typically lengthen the isoprenoid side chain of vitamin K to produce a range of vitamin K forms, most notably the MK - 7 to MK - 11 homologues of vitamin K. All forms of K other than MK - 4 can only be produced by bacteria, which use these forms in anaerobic respiration . The MK - 7 and other bacterially derived forms of vitamin K exhibit vitamin K activity in animals, but MK - 7's extra utility over MK - 4, if any, is unclear and is a matter of investigation . </P>

What are the main sources of vitamin k