Vitamin K describes a group of lipophilic vitamins that exist naturally in two forms: vitamin K1 (phylloquinone, found in green plants) and vitamin K2 (a group of menaquinones synthesised by bacteria in the intestine). Vitamin K3 (menadione) is a synthetic form of vitamin K that is used in agricultural animal feeds.
Vitamin K is fat-soluble and known as the clotting vitamin, because without it blood would not clot. It serves as a coenzyme in the formation of various blood clotting factors. It is used in the body for synthesising the liver
protein that controls blood clotting. It is involved in creating the important prothrombin, which is the precursor to thrombin, a very important factor in blood clotting. It is also involved in bone formation and repair. In the intestines it also assists in converting glucose to glycogen, which is then stored in the liver to be used as energy when required.
also reduce the risk of bleeding in liver disease, jaundice, malabsorption or in association with long-term use of aspirin or antibiotics. Vitamin K-rich foods can help people with digestive disorders such as Crohn's disease to absorb nutrients better.
Vitamin K1 helps prevent excessive activation of osteoclasts, the cells that break down bone. Beneficial bacteria in the intestines convert vitamin K1 into vitamin K2, which activates osteocalcin, the major non-collagen protein in bone. Osteocalcin anchors calcium molecules inside of the bone. All of these vitamin K-related mechanisms point to the importance of vitamin K-rich foods for bone and heart health.
The benefit of vitamin D, where bone strength and cardiovascular health are concerned, is greatly enhanced when combined with vitamin K2. Vitamin D improves bone health by helping the body absorb calcium. However, it is vitamin K2 that directs calcium to the skeleton, to prevent it from being deposited in the wrong areas such as around the heart. Vitamin K2 (menaquinones) only occurs in foods of animal origin or foods altered by bacterial fermentation. See below.
Vitamin K2 is linked to cardiovascular health and is essential for regulating proteins in the body that direct calcium to the bones and keep it out of the arterial walls and organs where it can do harm. Low vitamin K in aging humans can lead to vascular calcification, chronic inflammation and a seriously higher risk of heart attack and strokes. Vitamin K blood tests assess levels of vitamin K to maintain healthy coagulation, but at this time are not used to identify optimal levels of K2 to reduce heart attack risk.