Vitamin K


Vitamin K is a vitamin found in leafy green vegetables, broccoli, and Brussels sprouts. The name vitamin K comes from the German word "Koagulationsvitamin."

Several forms of vitamin K are used around the world as medicine. Vitamin K1 (phytonadione) and vitamin K2 (menaquinone) are available in North America. Vitamin K1 is generally the preferred form of vitamin K because it is less toxic and works faster for certain conditions.

Vitamin K is most commonly used for blood clotting problems or for reversing the blood thinning effects of warfarin. It is also used for many other conditions, but there is no good scientific evidence to support most of these other uses.


Is a Form of:


Primary Functions:

Blood clotting problems

Also Known As:

2-methyl-1,4-naphthoquinone, 2-methyl-3-phytyl-1,4-naphthoquinone

How Does It Work?

Vitamin K is an essential vitamin that is needed by the body for blood clotting and other important processes.


  • Bleeding problems in newborns with low levels of vitamin K (hemorrhagic disease). Giving vitamin K1 by mouth or as a shot into the muscle helps prevent bleeding problems in newborns. Shots seem to work the best.
  • Low levels of the blood clotting protein prothrombin (hypoprothrombinemia). Taking vitamin K1 by mouth or as an injection into the vein can prevent and treat bleeding problems in people with low levels of prothrombin due to using certain medications.
  • A rare, inherited bleeding disorder (vitamin K-dependent clotting factors deficiency or VKCFD). Taking vitamin K by mouth or as an injection into the vein can help prevent bleeding in people with VKCFD.
  • Reversing the blood thinning effects of warfarin. Taking vitamin K1 by mouth or as in injection into the vein can reverse too much blood thinning caused by warfarin. However, injecting vitamin K1 under the skin does not seem to work. Taking vitamin K along with warfarin also seems to help stabilize blood clotting time in people taking warfarin. It works best in people who have low vitamin K levels.
  • Weak and brittle bones (osteoporosis).Taking a specific form of vitamin K2 seems to improve bone strength and reduce the risk of fracture in most older women with weak bones. But it doesn't seem to benefit older women who still have strong bones. Taking vitamin K1 seems to increase bone strength and might prevent fractures in older women. But it might not work as well in older men. Vitamin K1 doesn't seem to improve bone strength in women who have not gone through menopause or in people with Crohn disease.

Recommended Dosing

The following doses have been studied in scientific research:



  • For weak and brittle bones (osteoporosis): The MK-4 form of vitamin K2 has been taken in doses of 45 mg daily. Also, vitamin K1 has been taken in doses of 1-10 mg daily.
  • For a rare, inherited bleeding disorder (vitamin K-dependent clotting factors deficiency or VKCFD): 10 mg of vitamin K has been taken 2-3 times weekly.
  • For reversing the blood thinning effects of warfarin: A single dose of 1-5 mg of vitamin K1 is typically used to reverse the effects of taking too much warfarin. The exact dose needed is determined by a lab test called the INR. Daily doses of 100-200 micrograms of vitamin K have been used for people taking warfarin long-term who have unstable blood clotting.


  • For a rare, inherited bleeding disorder (vitamin K-dependent clotting factors deficiency or VKCFD): 10 mg of vitamin K has been injected into the vein. How often these injections are given is determined by a lab test called the INR.
  • For reversing the blood thinning effects of warfarin: A single dose of 0.5-3 mg of vitamin K1 is typically used. The exact dose needed is determined by a lab test called the INR.



  • For bleeding problems in newborns with low levels of vitamin K (hemorrhagic disease): 1-2 mg of vitamin K1 has been given in three doses over 8 weeks. Also single doses containing 1 mg of vitamin K1, 5 mg of vitamin K2, or 1-2 mg of vitamin K3 have been used.


  • For bleeding problems in newborns with low levels of vitamin K (hemorrhagic disease): 1 mg of vitamin K1 has been given as a shot into the muscle.

There isn't enough scientific information to determine recommended dietary allowances (RDAs) for vitamin K, so daily adequate intake (AI) recommendations are used instead: The AIs are: infants 0-6 months, 2 mcg; infants 7-12 months, 2.5 mcg; children 1-3 years, 30 mcg; children 4-8 years, 55 mcg; children 9-13 years, 60 mcg; adolescents 14-18 years (including those who are pregnant or breast-feeding), 75 mcg; men over 19 years, 120 mcg; women over 19 years (including those who are pregnant and breast-feeding), 90 mcg.

Vitamin K Supplements Frequently Asked Questions

Should I take a vitamin K supplement?

The recommended adequate intake of vitamin K you take in, both from food and other sources is below. Most people get enough vitamin K from their diets. There have been no adverse effects of vitamin K seen with the levels found in food or supplements. However, this does not rule out danger with high dose.

What is the best vitamin K supplement?

One study found that both phytonadione and MK-7 supplements are well absorbed, but MK-7 has a longer half-life [21]. Menadione, which is sometimes called "vitamin K3," is another synthetic form of vitamin K.

Is too much vitamin K bad for you?

If you take vitamin K supplements, don't take too much as this might be harmful. Taking 1mg or less of vitamin K supplements a day is unlikely to cause any harm.

What are the symptoms of low vitamin K?

The signs and symptoms associated with vitamin K deficiency may include:

  • Easy bruising.
  • Oozing from nose or gums.
  • Excessive bleeding from wounds, punctures, and injection or surgical sites.
  • Heavy menstrual periods.
  • Bleeding from the gastrointestinal (GI) tract.
  • Blood in the urineand/or stool.

Does vitamin D need vitamin K?

Vitamins D and K are both fat-soluble vitamins and play a central role in calcium metabolism. Vitamin D promotes the production of vitamin K-dependent proteins, which require vitamin K for carboxylation in order to function properly.

Do you need vitamin K with d3?

It's clear that vitamin K benefits your heart and bones, but it's unclear whether high-dose vitamin D supplements are harmful when you're low in vitamin K. Nevertheless, make sure to get adequate amounts of both vitamin D and K from your diet. Both of them are important.

Is it safe to take vitamin k2 supplements?

So far, results have been mixed. Some studies, many of them conducted in Japan, found that supplementation with vitamin K1 or vitamin K2 improved bone mineral density, and few studies showed a decreased risk of bone fractures. ... Vitamin K supplements are relatively safe, and many people take them.

What happens if you don't get enough vitamin K?

What happens if I don't get enough vitamin K? Severe vitamin K deficiency can cause bruising and bleeding problems because the blood will take longer to clot. Vitamin K deficiency might reduce bone strength and increase the risk of getting osteoporosis because the body needs vitamin K for healthy bones.

Does Vitamin k2 thicken your blood?

The Bottom Line

Vitamin K likely plays an important role in blood clotting and promoting good heart and bone health. Some research suggests that K2 may be superior to K1 in some of these functions, but further research is needed to confirm this.

Should you take vitamin k2 and d3 together?

Vitamin D3 and vitamin K2 ensure that calcium is absorbed easily and reaches the bone mass, while preventing arterial calcification. Helping to keep your heart and bones healthy. Separately, K2 regulates normal blood clotting, whilst D3 supports a healthy immune system and supports muscle function.

When should I take vitamin K?

Intravenous infusion is preferred in situations when more rapid reversal of anticoagulation is required. A significant effect on the INR is usually evident within 4-6 hours after IV administration of vitamin K. The required dose (usually 5-10 mg) is added to 50 mL of D5W and infused over 15-30 minutes.

What diseases are caused by lack of vitamin K?

Vitamin K deficiencies in newborns are associated with vitamin K deficiency bleeding or VKDB (also known as hemorrhagic disease of the newborn). This can cause excessive bleeding and bruising and, in severe cases, can lead to fatal bleeding into the brain.

What is the best way to get vitamin K?

The best way to get the daily requirement of vitamin K is by eating food sources. Vitamin K is found in the following foods: Green leafy vegetables, such as kale, spinach, turnip greens, collards, Swiss chard, mustard greens, parsley, romaine, and green leaf lettuce.

Which disease is caused due to lack of vitamin K?

Vitamin K deficiency bleeding (VKDB) is a bleeding problem that occurs in some newborns during the first few days of life. VKDB was previously called hemorrhagic disease of the newborn.

Is cheese high in vitamin K?

The richest sources of vitamin K1 are dark, leafy green vegetables. ... Natto, a Japanese dish made from fermented soybeans, is one of the best sources of vitamin K2. Other good sources include meat, liver and cheese ( 9 ).

Can too much vitamin K cause blood clots?

Abnormal clotting is not related to excessive vitamin K intake, and there is no known toxicity associated with vitamin K1 or vitamin K2 (see Toxicity). Some oral anticoagulants, such as warfarin (Coumadin, Jantoven), inhibit coagulation by antagonizing the action of vitamin K.

What is the difference between vitamin K and vitamin k2?

The Bottom Line

Vitamin K1 is primarily found in leafy green vegetables, while K2 is most abundant in fermented foods and some animal products. Vitamin K2 may be absorbed better by the body and some forms may stay in the blood longer than vitamin K1.

Is vitamin K deficiency common?

Vitamin K deficiency is rare in adults because many of the foods we eat contain adequate amounts of K1, and because the body makes K2 on its own. ... Vitamin K deficiency is much more common in infants. In infants, the condition is called VKDB, for vitamin K deficiency bleeding.

What is the toxicity of vitamin K?

Vitamin K toxicity is extremely rare. The only reported toxicity comes from menadione, which has no use in humans. Its toxicity is thought to be associated with its water-soluble properties. When toxicity does occur, it manifests with signs of jaundice, hyperbilirubinemia, hemolytic anemia, and kernicterus in infants.

Can vitamin K be used to stop bleeding?

Vitamin K is used to treat and prevent low levels of certain substances (blood clotting factors) that your body naturally produces. These substances help your blood to thicken and stop bleeding normally (e.g., after an accidental cut or injury).

Does vitamin K really stop your period?

Vitamin A is needed for normal oestrogen levels and for normal menstrual bleeding. Cod liver oil provides a natural source of vitamin A. Vitamin K is needed for normal blood clotting, and therefore healthy menstrual bleeding. This is good news as it may lead to lighter periods.

Clinical Studies