Also known as clotting vitamins. A fat-soluble vitamin composed of naphthoquinone compounds that can promote blood coagulation. Widely found in green plants such as alfalfa and spinach, pig liver and egg yolk are also rich in vitamin K. 1929 Tim found that there are two kinds of vitamin K in nature: K 1 and K2, and there are no naphthoquinones. Vitamin K 1 is a yellow oil, and vitamin K2 is a yellow crystal, which is soluble in oil and organic solvents such as acetone and ether. Heat-resistant but easily damaged by light. Vitamin K has certain function on photosynthesis in plants. It is an essential factor to produce prothrombin in animals, so it can promote blood coagulation. There is no recognized regulation on the minimum daily requirement of vitamin K for human beings. Animals lack vitamin K, and the blood coagulation time is prolonged, which can cause trauma and bleeding. Adults are generally not easy to lack vitamin K, because there are abundant green plants in nature, and some bacteria in human intestines can synthesize vitamin K and supply it to the host. Sometimes newborns or patients with bile duct obstruction will have prolonged coagulation time due to vitamin K deficiency. Therefore, vitamin K preparation can be used to stop bleeding in clinic.