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Vitamins & Minerals Q&AVitamin K

About vitamin K

Vitamin K is a fat-soluble vitamin that is necessary for blood coagulation. The “K” in vitamin K is not related to the order in which the vitamin was discovered, but is derived from the German word “koagulation,” which means coagulation. Vitamin K can be found in foods such as green leafy vegetables, eggs, meat, dairy products, and Japanese natto (fermented soy beans). As vitamin K is contained in a wide variety of foods, healthy people rarely suffer from delayed blood clotting, which is a symptom of vitamin K deficiency. However, vitamin K deficiency can easily occur in newborn babies and infants.

Why might a doctor recommend limiting vitamin K intake if you suffer from atrial fibrillation?

The intention of this advice may well be due to the potential of vitamin K interacting with the drug Warfarin Potassium.

  • What is the drug generically known as Warfarin Potassium?
    Warfarin Potassium is a medication that reduces the formation of blood clots. It is prescribed for patients suffering from atrial fibrillation and other conditions.
  • How does vitamin K weaken the effect of Warfarin Potassium?
    Vitamin K, which is also known as an anti-hemorrhagic factor, is involved in reactions in the body that make blood clot. Specifically, it is involved in the action of four blood coagulation factors and three proteins. Meanwhile, Warfarin Potassium inhibits the functioning of vitamin K, thus making it difficult for blood to clot. In other words, because Warfarin Potassium and vitamin K work in opposing ways, they each weaken the action of the other.
  • What foods do I need to be careful about eating?
    The guidance for use that come with Warfarin Potassium lists “alcohol, natto, foods containing chlorella, green juices, and St. John's Wort” as “foods that can weaken the effect of Warfarin Potassium.” (However, alcohol and St. John's Wort interfere with the action of Warfarin Potassium through a different mechanism).
    Warfarin Potassium is sometimes used to treat conditions such as atrial fibrillation. Because Warfarin Potassium acts as a competitive inhibitor of vitamin K, it is clear that it does not function properly when there are high levels of vitamin K in the blood. Therefore, people who are taking warfarin should first consult their physician before taking any supplements.