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What is vitamin K?

A number of chemicals called naphthoquinone compounds are collectively classified as vitamin K. All of the various forms of vitamin K are fat soluble, which means they require the presence of fat in order to be absorbed from the intestinal tract into the bloodstream, and that they are carried through the blood by a protein that can transport fat (a lipoprotein). Like all fat-soluble vitamins, K is stored in the liver or fatty tissues.

Many foods contain vitamin K. Especially good sources include spinach and other green, leafy vegetables, cereal grains, cabbage, and liver. In addition, vitamin K is manufactured by bacteria in the intestinal tract.

Why is vitamin K important to nutrition?

The liver needs vitamin K in order to manufacture clotting factors, 10 special proteins that enable the blood to coagulate or form clots. Vitamin K is an essential component of four of these factors: factor II {prothrombin) and factors VII, IX, and X. Prothrombin is a precursor of thrombin, one of the major factors in the formation of clots.

Although vitamin K is best known for its role in blood function, recent research indicates that it may have additional functions. For example, it seems to have a role in proper bone metabolism, but precisely what this role may be is unknown.

How much vitamin K do I need?

The revised 1989 Recommended Dietary Allowances (RDAs) for vitamin K, stated in micrograms, call for the following amounts:

• 5 for infants up to 6 m onths of age.
• 10 for infants 6 to 12 months.

Sampling of foods high in vitamin K.

• 15 for children 1 to 3 years.
• 20 for children 4 to 6 years.
• 30 for children 7 to 10 years.
• 45 for children 11 to 15 years.
• 55 for females 15 to 18 years.
• 65 for males 15 to 18 years.
• 60 for females 19 to 24 years.
• 70 for males 19 to 24 years.
• 65 for females over 25 years, including during pregnancy and lactation.
• 80 for males over 25 years.

What happens if I don't get enough vitamin K?
Easy bruising and excessive bleeding are the major consequences of a vitamin K deficiency. Purpura, the development of small, purplish dots under the skin, is another sign of vitamin K deficiency. In unusual cases, vitamin K deficiency may cause liver damage.

Vitamin K deficiency is particularly hazardous for women during childbirth and for patients undergoing surgery— times when a certain amount of blood loss is to be expected even under normal circumstances. In such cases, vitamin K may be given by injection to halt blood loss.

Since vitamin K is manufactured in the body and consumed in the diet, deficiency is uncommon. However, newborn babies lack the intestinal bacteria that make

Vitamin K is needed to make fibrin, the substance that binds blood platelets together to form clots.

vitamin K, so they may develop a deficiency, especially if their mothers had low reserves of the vitamin. In adults, deficiency can develop as a result of long-term use of antibiotics, which destroy the intestinal bacteria that manufacture vitamin K. Prolonged bleeding can cause deficiency, as can kidney disease, cancer, or intestinal disorders that interfere with the absorption of fats and, consequently, of vitamin K as well.

What happens if I get too much vitamin K?
It is impossible to get too much vitamin K from diet alone. Infants who are given excessive vitamin K supplements may develop jaundice, a yellowing of the skin and eyes due to a liver disorder. Otherwise, adverse effects of excessive vitamin K are unknown.

Should I take vitamin K supplements?
Vitamin K supplements are needed only under unusual circumstances and should not be taken unless prescribed by a doctor. Sometimes doctors administer vitamin K to reverse the effects of heparin or other anticoagulant medications that interfere with blood clotting. A person taking antibiotics may need to increase his or her intake of foods high in vitamin K, but vitamin K supplements should not be taken unless a doctor prescribed them.

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