Vitamin K is an essential fat-soluble vitamin that plays a vital role in the production of coagulation proteins, is found in green leafy vegetables and oils, such as soybean, cottonseed, canola, and olive oil. Coagulation refers to blood clotting, because Vitamin K is essential for the functioning of several proteins involved in blood clotting. Specifically, Vitamin K is required for the liver to make factors that are necessary for blood to properly clot (coagulate), including factor II (prothrombin), factor VII (proconvertin), factor IX (thromboplastin component), and factor X (Stuart factor). Other clotting factors that depend on Vitamin K are protein C, protein S, and protein Z. Deficiency of Vitamin K or disturbances of liver function (for example, severe liver failure) may lead to deficiencies of clotting factors and excess bleeding. Vitamin K is found in a number of foods, including leafy greens, cauliflower and, if you consider it a food, liver. However, the chief source of Vitamin K is synthesis by bacteria in the large intestine, and in most cases, absence of dietary Vitamin K is not at all deleterious. As it is a fat-soluble vitamin and both dietary and microbial Vitamin K are absorbed into intestinal lymph along with other lipids. The fetus obtains Vitamin K from its mother by transplacental transfer.
Vitamin K supplements improve bone health and reduce risk of bone fractures, particularly in postmenopausal women who are at risk for osteoporosis. It is used to reduce risk of bleeding in liver disease, jaundice, malabsorption, or in association with long-term use of aspirin or antibiotics. Overt Vitamin K deficiency results in impaired blood clotting, usually demonstrated by laboratory tests that measure clotting time. Symptoms include easy bruising and bleeding that may be manifested as nosebleeds, bleeding gums, blood in the urine, blood in the stool, tarry black stools, or extremely heavy menstrual bleeding. In infants, Vitamin K deficiency may result in life-threatening bleeding within the skull (intracranial hemorrhage). Vitamin K is indicated in those with Vitamin K deficiency, in some cases of hemorrhagic disease of the newborn, in some malabsorption syndromes and in some on long-term total parenteral nutrition. There is emerging evidence that adequate Vitamin K intake may help protect against osteoporosis generally.
References:
Linus Pauling Institute. http://lpi.oregonstate.edu/infocenter/vitamins/vitaminK/
Medline Plus. http://www.nlm.nih.gov/medlineplus/druginfo/natural/patient-vitamink.html
http://www.vivo.colostate.edu/hbooks/pathphys/misc_topics/vitamink.html
PDR Health. http://www.pdrhealth.com/drug_info/nmdrugprofiles/nutsupdrugs/vit_0267.shtml
