Vitamin K comes in two forms, K1 and K2, each having its own specific function in the body. Vitamin K is so called from the word coagulation. Coagulation is the process in which blood forms clots. Vitamin K facilitates the function of several proteins, including those that are responsible for blood clot formation. K1 is primarily used for this. It plays a vital role in cell growth and in the metabolism of bone and other tissues. Vitamin K2 plays an important role in bone formation. It is also involved in the prevention of bone loss. Vitamin K modifies the protein osteocalcin. This gives osteocalcin the ability to bind to calcium, and direct calcium to where it is needed to form the bone matrix. Vitamin K also works with vitamin D to facilitate the function of osteoblasts, the bone building cells. Vitamin K is found in leafy green vegetables, blueberries and tomatoes.