Diseases & Conditions


Vitamin K

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 can be absorbed. In some countries, this form is used for supplementation.

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 Deficiency

Bleeding, the main symptom, can be life threatening in newborns. Blood tests to check coagulation can confirm the diagnosis. All newborns should be given a vitamin K injection. Vitamin K supplements taken by mouth or injected under the skin can correct the deficiency.

Vitamin K deficiency can result from lack of vitamin K in the diet or from disorders that impair fat absorption and that thus reduce the absorption of vitamin K. Taking large amounts of mineral oil may reduce the absorption of vitamin K. Vitamin K deficiency can develop in people who take certain drugs, including anticonvulsants and some antibiotics. Doctors frequently prescribe vitamin K antagonists (anticoagulants such as warfarin Some Trade Names COUMADIN ) to people who are at high risk for harmful blood clots, such as those with deep vein thrombosis (DVT), pulmonary embolism, or irregular heart rhythms (such as atrial fibrillation).

Newborns are prone to vitamin K deficiency because only small amounts of vitamin K cross the placenta and because, during the first few days after birth, their intestine does not contain bacteria to produce vitamin K. The 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.

Did You Know...

Newborns are at risk of vitamin K deficiency because they receive only a little vitamin K before birth and they have not yet acquired the bacteria that produce the vitamin.


The main symptom 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. In newborns, life-threatening bleeding within or around the brain may occur. Having a liver disorder increases the risk of bleeding because proteins that help blood clot (clotting factors) are made in the liver. Vitamin K deficiency may also weaken bones.

Diagnosis and Treatment

Doctors suspect vitamin K deficiency when abnormal bleeding occurs in people with conditions that put them at risk. Blood tests to measure how well blood clots are done to help confirm the diagnosis. Knowing how much vitamin K people consume helps doctors interpret results of the blood test.

A vitamin K injection in the muscle is recommended for all newborns to reduce the risk of bleeding within the brain after delivery. Otherwise, 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.

People who have vitamin K deficiency and a severe liver disorder may also need blood transfusions to replenish the clotting factors. A damaged liver may be unable to synthesize clotting factors even after vitamin K injections are given.

Last full review/revision August 2007 by Larry E. Johnson, MD, PhD

Source: The Merck Manual Home Edition