Vitamin K

Other name(s):

antihemorrhagic factor, menadiol, menadione (vitamin K-3), menaquinone (vitamin K-2), methylphytyl naphthoquinone, phylloquinone (vitamin K-1), phytonadione

General description

Vitamin K, one of the fat-soluble vitamins, is involved in promoting blood clotting.

The major source of vitamin K, phylloquinone, is found in green plants. Another form of vitamin K, menaquinone, is produced by bacteria living in the intestine. Menadione, the synthetic form of vitamin K, is the most potent, with twice the activity of phylloquinone. However, some experts say that humans may not absorb as much of this bacterial-produced vitamin K as previously thought.

Vitamin K is necessary for the normal coagulation, or clotting, of blood. Warfarin, a chemical used in rat and mouse poison, has been adapted for medical purposes because it blocks the effects of vitamin K. This allows the physician to prevent abnormal blood clots and treat conditions like phlebitis (clots in the inflamed veins in the legs) and pulmonary emboli (blood clots). Excessive warfarin may cause spontaneous bleeding that can result in stroke, gastrointestinal bleeding, and death.

Medically valid uses

Vitamin K is used in the prevention and treatment of certain coagulation (clotting) disorders. Vitamin K is also used to prevent hemorrhagic disease (severe bleeding) in newborns.

Vitamin K may be used therapeutically in cases of prolonged intravenous feeding and in situations in which exposure to antibiotics has killed vitamin K-producing bacteria in the intestines.

Unsubstantiated claims

Please note that this section reports on claims that have NOT yet been substantiated through scientific studies.

Research is being done to observe the effect of vitamin K on osteoporosis and bone health. Vitamin K is also being studied for its possible benefits in protecting against cancer.

Recommended intake

As indicated below, vitamin K is measured in micrograms (mcg). Information is not currently supplied in International Units. The RDA is the Recommended Dietary Allowance.



Infants (0 to 6 months)

5 mcg

Infants (6 months to 1 year)

10 mcg

Children (1 to 3 years)

15 mcg

Children (4 to 6 years)

20 mcg

Children (7 to 10 years)

30 mcg

Youth (11 to 14 years)

45 mcg

Boys (15 to 18 years)

65 mcg

Girls (15 to 18 years)

55 mcg

Men (19 to 24 years)

70 mcg

Women (19 to 24 years)

60 mcg

Men (25 + years)

80 mcg

Women (25 + years)

65 mcg

Pregnant women

65 mcg

Breastfeeding women

65 mcg

A normal diet supplies adequate amounts of vitamin K. Although vitamin K is not dispensed as a nutritional supplement, small amounts are available in some multivitamins, or it is available by prescription.

Food source

Nutrient content per 100 grams

Cheddar cheese

22,220 mcg

Brussels sprouts

1,499 mcg

Green tea

711 mcg

Turnip greens

649.9 mcg


488 mcg


333 mcg


299.9 mcg


277 mcg


249 mcg


199.9 mcg

Vitamin K is stable at room temperature and therefore does not need to be refrigerated. It is not destroyed by cooking. However, light can cause some loss of activity; therefore, foods containing vitamin K should be stored in light-resistant containers.

An increased need for vitamin K may result from various malabsorption syndromes in which steatorrhea (excess fat in the stool) occurs. These syndromes include lactose intolerance, tropical and non-tropical sprue, celiac disease, cystic fibrosis, ulcerative colitis, and conditions that lead to a pancreatectomy (surgical removal of part or the entire pancreas).

Obstruction of the bile ducts, liver disease such as cirrhosis, and long-term treatment with antibiotics also increase the need for vitamin K.

Newborn infants need vitamin K. (All newborns are given a vitamin K injection within a few hours of birth. Without vitamin K, approximately 1 in 100 to 1,000 infants may experience some bleeding problems before their own vitamin K activity is high enough.) Premature infants, in particular, may be deficient in vitamin K.

Long-term treatment with antibiotics may lead to a need for vitamin K supplements.

Although vitamin K deficiencies are rare, signs of deficiency would include spontaneous bleeding or problems with blood clotting.

Side effects, toxicity, and interactions

The normal diet contains insufficient vitamin K to cause side effects. However, people who take Coumadin (warfarin sodium) for blood thinning should discuss their dietary intake with their physicians. Any change of diet that increases intake of vitamin K could counteract the effects of the Coumadin.

Vitamin K supplements should only be taken when prescribed by a physician.

Women who are pregnant or breastfeeding should consult a physician before taking any vitamin supplements.

Vitamin K interferes with the blood-thinning properties of warfarin (Coumadin).

Additional information

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