URL of this page: https://medlineplus.gov/druginfo/natural/983.html

Vitamin K

What is it?

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, works faster, is stronger, and works better for certain conditions.

Vitamin K is most commonly used for blood clotting problems. For example, vitamin K is used to reverse the effects of "blood thinning" medications when too much is given. It is also used to prevent clotting problems in newborns who don't have enough vitamin K. Vitamin K is also given to treat and prevent vitamin K deficiency, a condition in which the body doesn't have enough vitamin K.

An increased understanding of the role of vitamin K in the body beyond blood clotting led some researchers to suggest that the recommended amounts for dietary intake of vitamin K be increased. In 2001, the National Institute of Medicine Food and Nutrition Board increased their recommended amounts of vitamin K slightly, but refused to make larger increases. They explained there wasn't enough scientific evidence to make larger increases in the recommended amount of vitamin K.

How effective is it?

Natural Medicines Comprehensive Database rates effectiveness based on scientific evidence according to the following scale: Effective, Likely Effective, Possibly Effective, Possibly Ineffective, Likely Ineffective, Ineffective, and Insufficient Evidence to Rate.

The effectiveness ratings for VITAMIN K are as follows:

Effective for...

  • Preventing 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.
  • Treating and preventing bleeding problems in people with low levels of the blood clotting protein prothrombin. 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.
  • An inherited bleeding disorder called vitamin K-dependent clotting factors deficiency (VKCFD). Taking vitamin K by mouth or as an injection into the vein can help prevent bleeding in people with VKCFD.
  • Reversing the effects of too much warfarin used to prevent blood clotting. Taking vitamin K1 by mouth or as in injection into the vein can reverse too much blood clotting 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.

Possibly effective for...

  • Weak 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's disease.

Possibly ineffective for...

  • Bleeding within the fluid-filled areas (ventricles) of the brain (intraventricular hemorrhage). Giving vitamin K to women at risk for very preterm births does not seem to prevent bleeding in the brain of preterm infants. It also doesn't seem to reduce the risk of nerve injury caused by these bleeds.

Insufficient evidence to rate effectiveness for...

  • Blood disorder (beta-thalassemia). Early research shows that taking vitamin K2 by mouth along with calcium and vitamin D can improve bone mass in children with this blood disorder.
  • Breast cancer. Research suggests that higher dietary intake of vitamin K2 is linked with a lower risk of developing breast cancer.
  • Cancer. Some research has linked a higher food intake of vitamin K2, but not vitamin K1, with a reduced risk of death from cancer. But other research has linked a higher food intake of vitamin K1, but not vitamin K2, with a reduced risk of death from cancer.
  • Colorectal cancer. Early research suggests that a higher dietary intake of vitamin K is not linked with a reduced risk of cancer of the colon and rectum.
  • Heart disease. Higher dietary intake of vitamin K2 has been linked with a reduced risk of heart disease, risk factors for heart disease, and death due to heart disease in older men and women. But vitamin K2 intake from food does not seem to be linked with a reduced risk a heart disease in people at high risk for this condition. Dietary intake of vitamin K1 has not been linked with a reduced risk of heart disease. But increasing vitamin K1 intake from food has been linked with a reduced risk of death due to heart disease. Also, taking vitamin K1 as a supplement seems to prevent or reduce the advancement of coronary calcification. This is a risk factor for heart disease.
  • Cystic fibrosis. People with cystic fibrosis can have low levels of vitamin K due to problems digesting fat. Taking a combination of vitamins A, D, E, and K seems to improve vitamin K levels in people with cystic fibrosis who have trouble digesting fat. Also, early research shows that taking vitamin K by mouth for can enhance the production of osteocalcin. Osteocalcin plays a role in the body's bone-building and metabolic regulation. But there is no reliable evidence suggesting that vitamin K improves overall health in people with cystic fibrosis.
  • Diabetes. Early research shows that taking a multivitamin fortified with vitamin K1 does not lower the risk of developing diabetes compared to taking a regular multivitamin.
  • Skin rash associated with a type of cancer medicine. People who are given a certain type of anticancer medicine often develop skin rash. Early research shows that applying a cream containing vitamin K1 helps prevent skin rash in people being given this type of medicine.
  • High cholesterol. There is early evidence that vitamin K2 might lower cholesterol in people on dialysis with high cholesterol levels.
  • Liver cancer. Taking vitamin K2 does not seem to prevent liver cancer recurrence. But some early research shows that taking vitamin K2 reduces the risk of liver cancer in people with liver cirrhosis.
  • Lung cancer. Early research suggests that higher intake of vitamin K2 from food is linked with a reduced risk of lung cancer and lung cancer-related death. Dietary intake of vitamin K1 does not seem to be linked with a reduced risk of these events.
  • Multiple sclerosis (MS). Interferon is a medicine that helps people with MS. This medicine often causes a rash and burning of the skin. Early research shows that applying vitamin K cream modestly reduces rash and burning in people with treated with interferon.
  • Prostate cancer. Early research suggests that higher dietary intake of vitamin K2, but not vitamin K1, is linked with a reduced risk of prostate cancer.
  • Rheumatoid arthritis. Early research shows that taking vitamin K2 along with arthritis medicine reduces markers of joint swelling better than taking arthritis medicine alone.
  • Stroke. Population research suggests that dietary intake of vitamin K1 is not linked with a reduced risk of stroke.
  • Bruises.
  • Burns.
  • Scars.
  • Spider veins.
  • Stretch marks.
  • Swelling.
  • Other conditions.
More evidence is needed to rate vitamin K for these uses.

How does it work?

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

Are there safety concerns?

The two forms of vitamin K (vitamin K1 and vitamin K2) are LIKELY SAFE for most people when taken by mouth or injected into the vein appropriately. Most people do not experience any side effects when taking vitamin K in the recommended amount each day. However, some people may have an upset stomach or diarrhea.

Vitamin K1 is POSSIBLY SAFE for most people when applied as a cream that contains 0.1% vitamin K1.

Special precautions & warnings:

Pregnancy and breast-feeding: When taken in the recommended amount each day, vitamin K is considered safe for pregnant and breast-feeding women. Don't use higher amounts without the advice of your healthcare professional.

Children: The form of vitamin K known as vitamin K1 is LIKELY SAFE for children when taken by mouth or injected into the body appropriately.

Diabetes: The form of vitamin K known as vitamin K1 might lower blood sugar levels. If you have diabetes and take vitamin K1, monitor your blood sugar levels closely.

Kidney disease: Too much vitamin K can be harmful if you are receiving dialysis treatments due to kidney disease.

Liver disease: Vitamin K is not effective for treating clotting problems caused by severe liver disease. In fact, high doses of vitamin K can make clotting problems worse in these people.

Reduced bile secretion: People with decreased bile secretion who are taking vitamin K might need to take supplemental bile salts along with vitamin K to ensure vitamin K absorption.

Are there interactions with medications?

Do not take this combination.
Warfarin (Coumadin)
Vitamin K is used by the body to help blood clot. Warfarin (Coumadin) is used to slow blood clotting. By helping the blood clot, vitamin K might decrease the effectiveness of warfarin (Coumadin). Be sure to have your blood checked regularly. The dose of your warfarin (Coumadin) might need to be changed.
Be cautious with this combination.
Medications for diabetes (Antidiabetes drugs)
Vitamin K1 might decrease blood sugar. Diabetes medications are also used to lower blood sugar. Taking vitamin K1 along with diabetes medications might cause your blood sugar to go too low. Monitor your blood sugar closely. The dose of your diabetes medication might need to be changed.

Some medications used for diabetes include glimepiride (Amaryl), glyburide (DiaBeta, Glynase PresTab, Micronase), insulin, pioglitazone (Actos), rosiglitazone (Avandia), and others.

Are there interactions with herbs and supplements?

Coenzyme Q10
Coenzyme Q10 is chemically similar to vitamin K and, like vitamin K, can promote blood clotting. Using these two products together can promote blood clotting more than using just one. This combination can be a problem for people who are taking warfarin to slow blood clotting. Coenzyme Q10 plus vitamin K might overwhelm the effects of warfarin and could allow the blood to clot.
Herbs and supplements that might lower blood sugar
Vitamin K1 might lower blood sugar. Using vitamin K1 along with other herbs and supplements that might lower blood sugar might lower blood sugar too much. Herbs that might lower blood sugar include devil's claw, fenugreek, guar gum, Panax ginseng, and Siberian ginseng.
There is a concern that tiratricol might interfere with vitamin K's role in blood clotting.
Vitamin A
In animals, high doses of vitamin A interfere with vitamin K's ability to clot blood. But it's not known if this also happens in people.
Vitamin E
High doses of vitamin E (e.g. greater than 800 units/day) can make vitamin K less effective in clotting blood. In people who are taking warfarin to keep their blood from clotting, or in people who have low vitamin K intakes, high doses of vitamin E can increase the risk of bleeding.

Are there interactions with foods?

Butter, Dietary Fat
Eating foods containing butter or other dietary fats in combination with vitamin K-containing foods, such as spinach, seems to increase vitamin K absorption.

What dose is used?

The following doses have been studied in scientific research:


  • For 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 an inherited bleeding disorder called vitamin K-dependent clotting factors deficiency: 10 mg of vitamin K has been taken 2-3 times weekly.
  • For reversing the effects of warfarin: A single dose of 1-5 mg is typically used to reverse the effects of taking too much warfarin; however, the exact dose needed is determined by a lab test called the INR. Daily doses of 100-200 micrograms have been used for people taking warfarin long-term who have unstable blood clotting.
  • For an inherited bleeding disorder called vitamin K-dependent clotting factors deficiency: 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 effects of warfarin: A single dose of 0.5-3 mg is typically used; however, the exact dose needed is determined by a lab test called the INR.

  • For preventing 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 preventing 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 have been formed instead: The AIs are: infants 0-6 months, 2 mcg; infants 6-12 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.

Other names

4-Amino-2-Methyl-1-Naphthol, Fat-Soluble Vitamin, Menadiol Acetate, Menadiol Sodium Phosphate, Menadione, Ménadione, Menadione Sodium Bisulfite, Menaquinone, Ménaquinone, Menatetrenone, Menatétrenone, Phytonadione, Methylphytyl Naphthoquinone, Phylloquinone, Phytomenadione, Vitamina K, Vitamine K, Vitamine Liposoluble, Vitamine Soluble dans les Graisses.


To learn more about how this article was written, please see the Natural Medicines Comprehensive Database methodology.


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Last reviewed - 11/06/2017