Historical background
Vitamin K was discovered as the result of a series of experiments carried out by Henrik Dam on the possible essentiality of cholesterol in the diet of the chick. Dam (1929) noted that chicks ingesting diets which had been extracted with non-polar solvents to remove the sterols developed subdural or muscular hemorrhages and that blood taken from these animals clotted slowly.
Dam continued to study the distribution and lipid solubility of the active component in vegetable and animal sources, and proposed that the antihemorrhagic vitamin of the chick was a new fat-soluble vitamin which he called vitamin K (Dam, 1935a,b). Not only was K the first letter of the alphabet which was not used to describe an existing or postulated vitamin-like activity at that time, but it was also the first letter of the German word Koagulation.
Vitamin K is a fat-soluble vitamin required for normal BLOOD CLOTTING. As with VITAMIN E and VITAMIN B6, the term vitamin K represents several closely related forms: the most prevalent, naturally occurring forms are vitamin K1 (philloquinone or hytonadione) and vitamin K2 (menaquinone). Vitamin K3 is MENADIONE, a synthetic form that can be activated in the LIVER.
Vitamin K serves as a cofactor for the processing of six proteins required in the complex chain of reactions that regulates blood clotting. One of these proteins is prothrombin, the inactive precursor of the enzyme that creates fibrin clots from fibrinogen, and vitamin K has been used to treat clotting disorders due to vitamin K deficiency. Vitamin K also assists in the synthesis of osteocalcin, a bone protein that forms the matrix for mineralization and bone building.
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Possible Roles in Maintaining Health
Vitamin K is required for healing fractured bone and in the maintenance of normal bone. Elderly patients with osteoporosis (thin bone disease) may be low in vitamin K. Vitamin K supplementation may decrease calcium excretion and help protect against osteoporosis. A deficiency of vitamin K causes hemorrhaging. Pediatricians administer vitamin K to newborn infants to reduce their risk of spontaneous bleeding. Infants also run the risk of being permanently brain damaged by vitamin K deficiency in the first six months of life. There may be other important functions of this vitamin; vitamin K-dependent modified proteins occur in kidneys and other tissues as well, though their function is unclear.
Sources
Vitamin K occurs in highest levels in green, leafy vegetables. Dairy products are good sources, and small amounts occur in cereals, meats and other vegetables. Vitamin K occurs in low levels in breastmilk. Newborn infants are often given vitamin K to help their clotting mechanism. Bacteria colonizing the mature small intestine produce vitamin K; LACTOBACILLUS ACIDOPHILUS is an example of such a beneficial gut bacteria. Vitamin K3 is prescribed to treat vitamin K deficiencies.
Requirements
The RECOMMENDED DIETARY ALLOWANCE set forth by the government for normal adults is 80 mcg/day for men and 65 mcg/day for women. The OPTIMAL DOSE, however, appears to be 3 mg to 6 mg daily. SEE ABSTRACTS for more info. There are hints that optimal bone metabolism is more sensitive to inadequate vitamin K and the needs may be higher. Because vitamin K is widely distributed in food and is formed by normal gut flora, vitamin K deficiency is not believed to be common. Deficiency could occur in people who consume few vegetables, in people with LIPID MALABSORPTION and in those with CELIAC DISEASE or bile duct obstruction. The prolonged use of oral antibiotics; certain medications like cholesterol lowering drugs, mineral oil, anticonvulsants (Dilantin) and some antibiotics (cephalosporins); and PARENTERAL NUTRITION (venous feeding) increase the risk. Vitamin K status needs to be monitored in patients being treated with anticoagulants (like coumadin). Symptoms of severe deficiency include a tendency to bleed and disturbed bone formation.
Safety
Naturally occurring forms of vitamin K are relatively nontoxic. The synthetic form may rarely cause liver problems. An allergic-type reaction can occur with high doses. A high intake of vitamin E may cause bleeding similar to vitamin K deficiency. Those who have a vitamin K deficiency need medical supervision. Patients taking anticoagulants should take vitamin K only with the advice of a physician.