Vitamin K denotes a group of lipophilic, and hydrophobic, vitamins that are needed for the posttranslational modification of certain proteins, mostly required for blood coagulation. Chemically they are 2-methyl-1,4-naphthoquinone derivatives.
Vitamin K2 (menaquinone, menatetrenone) is normally produced by bacteria in the intestines, and dietary deficiency is extremely rare unless the intestines are heavily damaged.