Vitamin K is classified as a fat-soluble vitamin essential for the functioning of several proteins involved in blood clotting. There are two naturally occurring forms of vitamin K, one synthesized by plants (phylloquinone) and the other by the natural bcteria in the intestines (menaquinone). Synthetic form of vitamin K is called menadione. Vitamin K originates from the German term koajulation and is also known as antihemorrhagic factor because of its role in blood coagulation.
Vitamin K is required for normal blood clotting and synthesis of proteins that control clotting.
Blood clotting (coagulation): Coagulation is a process that begins when there is an injury to a blood vessel in the body. This solidifies the blood and prevents excessive bleeding which can lead to death. Vitamin K is required to activate many enzymes at different stages in the clotting process.
Bone mineralization: Vitamin K is involved in bone formation and repair and protects against osteoporosis. Higher vitamin K levels have been found to correspond to greater bone density, while low levels of vitamin K have been found in people with osteoporosis. Additionally, vitamin K appears to be important for the formation of cartilage and dentine which are important components of teeth. Vitamin K seems to play a role in preventing oxidative cell damage that is, preventing damage to cell structures by free radicals produced inside the body. Vitamin K functions as an antioxidant and inactivates these free radicals.
 Food Sources
Phylloquinone (vitamin K1) is the major dietary form of vitamin K.. Rich sources of dietary vitamin K include leafy vegetables like spinach, broccoli, asparagus, celery and cabbage. Other good sources include liver, egg yolk and some vegetable oils like soybean, canola and olive oil. Hydrogenation of vegetable oils may decrease the absorption and biological effect of dietary vitamin K. Some vitamin K is synthesized in the body in the intestines.
 Recommended Dosage
In 2000, the National Academy of Sciences established the following Adequate Intake (AI) levels for vitamin K:
- Males and females, 9-13 years: 60 micrograms
- Males and females, 14-18 years: 75 micrograms
- Males, 19 years and older: 120 micrograms
- Females, 19 years and older: 90 micrograms
- Pregnant or lactating females, 18 years and younger:75 micrograms
- Pregnant or lactating females, 19 years and older: 90 micrograms
What can high-vitamin K foods do for you?
Vitamin K deficiency is not very common in adults and is often the result of impaired absorption than dietary deficiency. It is of concern in newborns as their digestive tracts do not contain bacteria that produce vitamin K. Vitamin K deficiency results in increased blood clotting time which manifests itself in easy bruising, nosebleeds, bleeding gums and internal hemorrhaging. Severe vitamin K deficiency can also lead to fatal anemia.
Natural forms of vitamin K have not been known to produce symptoms of toxicity. However, although rare, allergic reactions to vitamin K supplements can occur. The symptoms of these allergic reactions include nausea, rash, itching and flushed skin. Injections of synthetic form of vitamin K (menadione) have been seen to induce liver toxicity, jaundice, and anemia (due to the rupture of red blood cells) in infants, and is no longer used for treatment of vitamin K deficiency.
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