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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 is one of the fat-soluble vitamins. It helps with blood clotting.

The major source of vitamin K is found in green plants. This form is called phylloquinone. Another form of vitamin K is made by bacteria living in the intestine. This form is called menaquinone. The synthetic form of vitamin K is called menadione. This form is the most potent. It has two times the activity of phylloquinone. But some experts say that humans may not absorb as much of this form of vitamin K as they had thought.

Vitamin K is needed for the normal clotting (coagulation) of blood. Warfarin is a medicine that blocks the effects of vitamin K. This medicine helps to prevent abnormal blood clots from forming. It is used for conditions, such as clots in the inflamed veins in the legs (thrombophlebitis) and blood clots in the lungs (pulmonary emboli). It helps to prevent new blood clots from forming. Too much warfarin may cause sudden bleeding. This can lead to stroke, gastrointestinal bleeding, and death.

Medically valid uses

Vitamin K is used to prevent and treat certain blood clotting (coagulation) issues. It’s also used to prevent severe bleeding (hemorrhagic disease) in newborns.

Vitamin K may be used in cases of ongoing IV feeding. It may also be used when antibiotics have killed bacteria in the intestines that make vitamin K.

Unproven claims

There may be benefits that have not yet been proven through research.

Research is being done to look at the effect of vitamin K on osteoporosis and bone health. Vitamin K is also being studied to see if it protects against cancer.

Recommended intake

Vitamin K is measured in micrograms (mcg). AI is the Adequate Intake.



Infants (0 to 6 months)

2 mcg

Infants (6 months to 1 year)

2.5 mcg

Children (1 to 3 years)

30 mcg

Children (4 to 8 years)

55 mcg

Children (9 to 13 years)

60 mcg

Children (14 to 18 years)

75 mcg

Men (19 years and older)

120 mcg

Women (19 years and older)

90 mcg

Pregnant and breastfeeding women (14 to 18 years)

75 mcg

Breastfeeding and breastfeeding women (19 years and older)

90 mcg

A normal diet gives enough vitamin K. Vitamin K is not sold as a single supplement. But small amounts are in some multivitamins. It’s also 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. It doesn’t need to be refrigerated. It isn’t destroyed by cooking. But light can cause some loss of effects. Store foods that have vitamin K in light-resistant containers.

You may need more vitamin K if you have any of these:

  • A malabsorption syndrome with steatorrhea (excess fat in the stool)

  • Lactose intolerance

  • Tropical and nontropical sprue

  • Celiac disease

  • Cystic fibrosis

  • Ulcerative colitis

  • Pancreatitis

  • Surgery to remove all or part of the pancreas (pancreatectomy)

  • Liver disease, such as cirrhosis

  • Blocked bile ducts

  • A long course of treatment with antibiotics

Newborn babies need vitamin K. All newborns are given a vitamin K injection within a few hours of birth. This is done because about 1 in 100 to 1,000 infants may have some bleeding problems before their own vitamin K level is high enough. Preterm babies may be low in vitamin K.

Vitamin K deficiency is rare. Signs of deficiency include sudden bleeding or problems with blood clotting. Vitamin K deficiency may also contribute to osteoporosis.

Side effects, toxicity, and interactions

A normal diet doesn’t contain enough vitamin K to cause side effects. But if you take warfarin for blood thinning, talk with your healthcare provider about your vitamin K intake. Any change of diet that increases or decreases intake of vitamin K could change the effects of the warfarin.

You should only take vitamin K supplements if your healthcare provider prescribes them to you.

People who are pregnant or breastfeeding should talk with their healthcare providers before taking any supplements.