All vitamin K variants are fat soluble and stable to heat. Alkalis, strong acids, radiation, and oxidizing agents can destroy vitamin K. It is absorbed from the upper small intestine with the help of bile or bile salts and pancreatic juices and then carried to the liver for the synthesis of prothrombin, a key blood-clotting factor. High intake (as with supplementation) of vitamin E or calcium may reduce vitamin K absorption. Vitamin K is stored in small amounts; most is excreted after therapeutic doses.

Yogurt, kefir, and acidophilus milk may help to increase the functioning of the intestinal bacterial flora and therefore contribute to vitamin K production. Antibiotics that reduce these bacteria will diminish vitamin K synthesis in the colon. Rancid oils and fats, X-rays, radiation, aspirin, air pollution, and freezing of foods all destroy vitamin K, and mineral oil binds with K and rapidly eliminates it from the intestines.

Sources: Vitamin K is found in both plant and animal sources in nature. Good supplies are found in the dark leafy greens, most green plants, alfalfa, and kelp. Blackstrap molasses and the polyunsaturated oils, such as safflower, also contain some vitamin K. In animal-source foods, K is found in liver, milk, yogurt, egg yolks, and fish liver oils. The best source for humans is that made by the intestinal bacteria. It is important for the production of many nutrients that we keep our "friendly" colon bacteria active and doing their job; to aid this process we should minimize our use of oral antibiotics, avoid excess sugars and processed foods, and occasionally evaluate and treat any abnormal organisms interfering in our colon, such as yeasts or parasites.

Functions: Vitamin K is necessary for normal blood clotting. It is required for the synthesis of prothrombin and other proteins (Factors IX, VII, and X) involved in blood coagulation. Vitamin K also helps prothrombin convert to thrombin with the aid of potassium and calcium; thrombin is the important factor needed for the conversion of fibrinogen to the active fibrin clot.

Coumarin, which comes from sweet clover, acts as an anticoagulant (decreases blood clotting) by competing with vitamin K at its active sites. Coumarin or synthetic dicumarol is used medically primarily as an oral anticoagulant to decrease prothrombin. The salicylates, such as aspirin, increase the need for vitamin K.

Uses: Vitamin K is used commonly by physicians in the treatment of clinical problems. It should not be taken routinely without the ability to monitor its effects on blood clotting. Currently, its most regular application in Western medicine is to inject newborns with vitamin K to prevent hemorrhage and other minor bleeding problems. Vitamin K is not transferred from the mother, nor are there colon bacteria to make it in newborns since the gastrointestinal tract is usually sterile for a few days after birth. The production of vitamin K and, therefore, prothrombin usually begins by the fourth day of life, giving babies their ability to clot blood when necessary.