Vitamin K2

Vitamin K2 or menaquinone is one of three types of vitamin K, the other two being Vitamin K1 (phylloquinone) and K3 (menadione). K2 is a bacterial product and is usually found in fermented foods or animal products.There are nine chemical variants of Vitamin K2, determined by number of isoprenyl units in their side chains. The most common in the human diet is the short-chain MK-4, which is usually produced by bacterial conversion of Vitamin K1, and is commonly found in animal products. Long-chain menaquinones include MK-7, MK-8 and MK-9 and are more predominant in fermented foods such as natto. Longer-chain menaquinones (MK-10 to MK-13) are produced by anaerobic bacteria in the colon, but they are not well absorbed and have little biological function. Vitamin K2, the main storage form in animals, has several subtypes, which differ in isoprenoid chain length. These vitamin K2 homologues are called menaquinones, and are characterized by the number of isoprenoid residues in their side chains. Menaquinones are abbreviated MK-n, where M stands for menaquinone, the K stands for vitamin K, and the n represents the number of isoprenoid side chain residues. For example, menaquinone-4 (abbreviated MK-4) has four isoprene residues in its side chain.