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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’s involved in blood clotting.

The major source of vitamin K, phylloquinone, is found in green plants. Another form of vitamin K, menaquinone, is made by bacteria living in the intestine. Menadione, the synthetic form of vitamin K, 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 bacterial-produced vitamin K as once thought.

Vitamin K is needed for the normal coagulation, or clotting, of blood. Warfarin, a chemical used in rat and mouse poison, has been adapted for medical uses. This is because it blocks the effects of vitamin K. This allows healthcare providers to prevent abnormal blood clots. It also treats conditions like phlebitis (clots in the inflamed veins in the legs) and pulmonary emboli (blood clots). Too much warfarin may cause spontaneous bleeding. This can lead to stroke, gastrointestinal bleeding, and death.

Medically valid uses

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

Vitamin K may be used therapeutically in cases of prolonged intravenous feeding. It may also be used 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 studies.

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 (0–6 months)

2 mcg

Infants (6 months to 1 year)

2.5 mcg

Children (1–3 years)

30 mcg

Children (4–8 years)

55 mcg

Children (9–13 years)

60 mcg

Children (14–18 years)

75 mcg

Men (19 years and older)

120 mcg

Women (19 years and older)

90 mcg

Pregnant and breastfeeding women (14–18 years)

75 mcg

Breastfeeding and breastfeeding women (19 years and older)

90 mcg

A normal diet supplies enough vitamin K. Although vitamin K is not dispensed as a nutritional supplement, small amounts are available 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 activity. For this reason, you should store foods containing vitamin K in light-resistant containers.

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

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

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

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

Vitamin K deficiencies are rare. Signs of deficiency include spontaneous bleeding or problems with blood clotting.

Side effects, toxicity, and interactions

A normal diet doesn’t contain enough vitamin K to cause side effects. However, people who take warfarin for blood thinning should talk about their vitamin K intake with their healthcare providers. Any change of diet that increases intake of vitamin K could counteract the effects of the warfarin.

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

Women who are pregnant or breastfeeding should talk to their healthcare providers before taking any supplements.

Medical Reviewers:

  • Poulson, Brittany, RD, CDE
  • Wilkins, Joanna, R.D., C.D.