Overview

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.

Uses & Effectiveness

Effective for

  • 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.

Possibly Effective for

  • 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.

Possibly Ineffective for

  • 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.

Side Effects

When taken by mouth: The two forms of vitamin K (vitamin K1 and vitamin K2) are likely safe when taken appropriately. A maximum daily dose of vitamin K hasn’t been set, but vitamin K1 10 mg daily and vitamin K2 45 mg daily have been safely used for up to 2 years. Some studied doses are much higher than recommendations for daily adequate intake. 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 and Warnings

When taken by mouth: The two forms of vitamin K (vitamin K1 and vitamin K2) are likely safe when taken appropriately. A maximum daily dose of vitamin K hasn’t been set, but vitamin K1 10 mg daily and vitamin K2 45 mg daily have been safely used for up to 2 years. Some studied doses are much higher than recommendations for daily adequate intake. 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.

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.

Interactions

    Moderate Interaction

    Be cautious with this combination

  • Warfarin (Coumadin) interacts with Vitamin K

    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.

Dosing

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.
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CONDITIONS OF USE AND IMPORTANT INFORMATION: This information is meant to supplement, not replace advice from your doctor or healthcare provider and is not meant to cover all possible uses, precautions, interactions or adverse effects. This information may not fit your specific health circumstances. Never delay or disregard seeking professional medical advice from your doctor or other qualified health care provider because of something you have read on WebMD. You should always speak with your doctor or health care professional before you start, stop, or change any prescribed part of your health care plan or treatment and to determine what course of therapy is right for you.

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