Vitamin K has two forms:
Phylloquinone: This form occurs in plants and is consumed in the diet. It is absorbed better when it is consumed with fat. Phylloquinone is not toxic.
Menaquinone: This form is produced by bacteria in the intestine, but only small amounts of it are produced. In some countries, this form is used for supplementation.
(See also Overview of Vitamins.)
Vitamin K is necessary for the synthesis of the proteins that help control bleeding (clotting factors) and thus for the normal clotting of blood. It is also needed for healthy bones and other tissues.
Vitamin K, like vitamins A, D, and E, is a fat-soluble vitamin, which dissolves in fat and is best absorbed when eaten with some fat. Good sources of vitamin K include green leafy vegetables (such as collards, spinach, and kale) and soybean and canola oils.
Vitamin K deficiency can cause hemorrhagic disease of the newborn, characterized by a tendency to bleed. A vitamin K injection is usually given to newborns to protect them from this disease. Breastfed infants who have not received this injection at birth are especially susceptible to vitamin K deficiency, because breast milk contains only small amounts of vitamin K. Hemorrhagic disease is more likely in infants who are breastfed or who have a disorder that impairs fat absorption or a liver disorder. Formulas for infants contain vitamin K. Risk is also increased if the mother has taken antiseizure drugs (such as phenytoin), anticoagulants (which make blood less likely to clot), or certain antibiotics.
In healthy adults, vitamin K deficiency is uncommon because many green vegetables contain vitamin K and bacteria in the intestine produce vitamin K.
If people have vitamin K deficiency, taking warfarin or related anticoagulants interfere with the synthesis of clotting factors (which help blood clot) and can make bleeding more likely or make it worse. Anticoagulants are given to people with conditions that increase the risk of blood clots. These conditions include having to stay in bed (for example, because of an injury or illness), recovering from surgery, and having atrial fibrillation (an abnormal, irregular heart rhythm). People who take warfarin need to have blood tests periodically to check how quickly their blood clots.
Vitamin K deficiency can result from the following:
Newborns are prone to vitamin K deficiency because of the following:
The main symptom of vitamin K deficiency is bleeding (hemorrhage)—into the skin (causing bruises), from the nose, from a wound, in the stomach, or in the intestine. Sometimes bleeding in the stomach causes vomiting with blood. Blood may be seen in the urine or stool, or stools may be tarry black.
In newborns, life-threatening bleeding within or around the brain may occur.
Having a liver disorder increases the risk of bleeding, because clotting factors are made in the liver.
Vitamin K deficiency may also weaken bones.
Doctors suspect vitamin K deficiency when abnormal bleeding occurs in people with conditions that put them at risk.
Blood tests to measure how quickly blood clots are done to help confirm the diagnosis. Knowing how much vitamin K people consume helps doctors interpret results of these blood tests. Sometimes the vitamin K level in the blood is measured.
A vitamin K injection in the muscle is recommended for all newborns to reduce the risk of bleeding within the brain after delivery.
If vitamin K deficiency is diagnosed, vitamin K is usually taken by mouth or given by injection under the skin. If a drug is the cause, the dose of the drug is adjusted or extra vitamin K is given.