Vitamin K refers to a group of fat-soluble vitamins that play a role in blood clotting, bone metabolism, and regulating blood calcium levels. Vitamin K is actually a group of compounds. The most important of these compounds appear to be vitamin K1 and vitamin K2. Research shows that low levels of vitamin K can raise the risk of uncontrolled bleeding. This is due to the fact that the body needs vitamin K to produce prothrombin, a protein, and clotting factor that is important in blood clotting and bone metabolism.