Have a question? This is a fact sheet intended for health professionals. For a reader-friendly overview of Vitamin K, see our consumer fact sheet on Vitamin K. These compounds include phylloquinone vitamin K1 and a series of menaquinones vitamin K2 [ 2 ]. Menaquinones have unsaturated isoprenyl side chains and are designated as MK-4 through MK, based on the length of their side chain [ 1, 2 ]. Phylloquinone is present primarily in green leafy vegetables and is the main dietary form of vitamin K [ 3 ]. Menaquinones, which are predominantly of bacterial origin, are present in modest amounts in various animal-based and fermented foods [ 1, 4 ]. Almost all menaquinones, in particular the long-chain menaquinones, are also produced by bacteria in the human gut [ 5, 6 ].
Vitamin K refers to structurally similar, fat-soluble vitamers found in foods and marketed as dietary supplements. The presence of uncarboxylated proteins indicates a vitamin K deficiency. Carboxylation allows them to bind chelate calcium ions, which they cannot do otherwise. Research suggests that deficiency of vitamin K may also weaken bones, potentially contributing to osteoporosis, and may promote calcification of arteries and other soft tissues. Chemically, the vitamin K family comprises 2- methyl – 1,4-naphthoquinone 3- derivatives. Vitamin K includes two natural vitamers: vitamin K 1 phylloquinone and vitamin K 2 menaquinone. The two most studied ones are menaquinone-4 MK-4 and menaquinone-7 MK Vitamin K 1 is made by plants, and is found in highest amounts in green leafy vegetables, because it is directly involved in photosynthesis. 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 2, variant MK Bacteria in the gut flora can also convert K 1 into MK
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Learn more x. The generic term vitamin K is now used to describe not a single chemical entity, but a group of quinone compounds that have characteristic anti-hemorrhagic effects and are fat soluble. The basic molecule is a naphthoquinone, and the various isomers differ in the nature and length of the side chain. Vitamin K-active compounds from material that had undergone bacterial fermentation were named menaquinones or vitamin K2. The simplest form of vitamin K is the synthetic menadione K3, which has no side chain. Menaquinone-4 is synthesized in the liver from ingested menadione or changed to a biologically active menaquinone by intestinal microorganisms. Naturally occurring sources of vitamin K are fat soluble; stable to heat; and is destabilized by oxidation, alkali conditions, strong acids, light and irradiation.