Vitamin k
Vitamin k


Vitamin K is a group of vitamins found in some green vegetables. Vitamins K1 (phytonadione) and K2 (menaquinone) are commonly available as supplements.

Vitamin K is an essential vitamin needed by the body for blood clotting, bone building, and other important processes. It's found in leafy green vegetables, broccoli, and Brussels sprouts. The name vitamin K comes from the German word "Koagulationsvitamin."

People commonly use vitamin K for blood clotting problems or for reversing the blood thinning effects of warfarin. It is also used for osteoporosis, athletic performance, breast cancer, diabetes, and many other conditions, but there is no good scientific evidence to support most of these other uses.
When taken by mouth: The two forms of vitamin K (vitamin K1 and vitamin K2) are likely safe when taken appropriately. Vitamin K1 10 mg daily and vitamin K2 45 mg daily have been safely used for up to 2 years. It's usually well-tolerated, but some people may have an upset stomach or diarrhea.

When applied to the skin: 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: Vitamin K is likely safe when taken in recommended amounts of 90 mcg daily for those over 19 years old. Don't use higher amounts without the advice of a healthcare professional.

Children: Vitamin K1 is likely safe when taken by mouth appropriately.

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 might not absorb vitamin K supplements very well. People with this condition might need to take supplemental bile salts along with vitamin K to improve absorption.


NatMed Pro 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.
  • Bleeding problems in newborns with low levels of vitamin K (hemorrhagic disease). Giving newborns vitamin K1 by mouth or as a shot into the muscle helps prevent bleeding. Shots seem to work the best, but can only be given by a healthcare provider.
  • Low levels of the blood clotting protein prothrombin (hypoprothrombinemia). Taking vitamin K1 by mouth or by IV can prevent and treat bleeding problems in people with low levels of prothrombin. IV products can only be given by a healthcare provider.
  • A rare, inherited bleeding disorder (vitamin K-dependent clotting factors deficiency or VKCFD). Taking vitamin K by mouth or by IV can help prevent bleeding in people with VKCFD. IV products can only be given by a healthcare provider.
  • Reversing the blood thinning effects of warfarin. Taking vitamin K1 by mouth or by IV can reverse the effects of warfarin, a blood thinner. IV products can only be given by a healthcare provider.
Likely effective Effectiveness definitions
Possibly effective Effectiveness definitions
  • Weak and brittle bones (osteoporosis). Taking vitamin K2 and vitamin K1 by mouth seems to improve bone strength and reduce the risk of fractures in people with weak bones. But it doesn't seem to benefit those who still have strong bones.
Likely ineffective Effectiveness definitions
Possibly ineffective Effectiveness definitions
  • Bleeding into or around the fluid-filled areas (ventricles) of the brain (intraventricular hemorrhage). Taking vitamin K by mouth while pregnant doesn't 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.
There is interest in using vitamin K for a number of other purposes, but there isn't enough reliable information to say whether it might be helpful.
Insufficient evidence Effectiveness definitions

Dosing & administration

Vitamin K is an essential vitamin. It is found in leafy green vegetables, broccoli, and Brussels sprouts.

It's recommended that males over 19 years old consume 120 mcg daily, and females over 19 years old consume 90 mcg daily. While pregnant and breast-feeding, 90 mcg should be consumed daily. Recommended amounts for children depend on age. Speak with a healthcare provider to find out what dose might be best for a specific condition.

Interactions with pharmaceuticals

Warfarin (Coumadin)

Interaction Rating=Major Do not take this combination.

Vitamin K is used by the body to help the blood clot. Warfarin is used to slow blood clotting. By helping the blood clot, vitamin K might decrease the effects of warfarin. Be sure to have your blood checked regularly. The dose of your warfarin might need to be changed.

Interactions with herbs & supplements

Coenzyme Q10: Vitamin K helps the blood to clot. Coenzyme Q10 can have some of the same effects as vitamin K. Taking coenzyme Q10 and vitamin K together can increase blood clotting. This can be a problem for people who are taking blood thinners. Coenzyme Q10 plus vitamin K might overwhelm the effects of blood thinners.
Tiratricol: There is some concern that tiratricol might interfere with the effects of vitamin K. But it's not clear if this is a big concern.
Vitamin A: There is some concern that high doses of vitamin A might interfere with the effects of vitamin K. But it's not clear if this is a big concern.
Vitamin E: High doses of vitamin E (e.g. greater than 800 units/day) can reduce the effects of vitamin K for blood clotting. In people who take warfarin, a blood thinner, or in people who have low vitamin K intakes, high doses of vitamin E can increase the risk of bleeding.

Interactions with foods

Eating foods containing butter or other dietary fats together with vitamin K-containing foods, such as spinach, seems to increase vitamin K absorption.
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This monograph was last reviewed on 15/08/2022 23:54:02 and last updated on 27/10/2020 02:57:04. Monographs are reviewed and/or updated multiple times per month and at least once per year.
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