Warfarin and Vitamin K: Relationship and Interaction

Instructor: Artem Cheprasov

Artem has a doctor of veterinary medicine degree.

This lesson defines and covers the important aspects of vitamin K and warfarin and then proceeds to outline how the two interact with respect to the formation of a blood clot.

Drug Interactions

Probably the most famous drug interactions result from mixing alcohol with other drugs. It's never a good combination. And you've certainly seen medication that warns you not to take it with alcohol, or within a period of time before or after you've consumed alcohol.

But drug interactions are not limited to medication plus alcohol. There are many more things that can mix negatively in your system, including the interaction of an important vitamin, vitamin K, and a famous medication called warfarin.

We'll briefly cover the importance of both and then tie them together in this lesson.

What Is Vitamin K?

Vitamin K is a type of fat soluble vitamin. In other words, it can be stored in your body's fat for the long term, and is therefore harder for your body to get rid of quickly than a water soluble molecule, like vitamin C.

Vitamin K can be obtained from many different foods, like leafy green vegetables (think spinach). However, what's really cool is that the bacteria found in your gut also make this vitamin for you! But just how much of that bacteria-made vitamin K is actually absorbed by your body is a subject of debate.

Regardless, have you ever wondered why vitamin K is called vitamin K and not vitamin J or something else? The K comes from the German for Koagulations-vitamin. Did you spot the word Koagulations? If you thought it sounds like, and might even mean, coagulation, you're right. And that is exactly what vitamin K is so critical for: coagulation, which is just another way of referring to the formation of a blood clot.

What Is Warfarin?

While vitamin K is important for coagulation, warfarin is an anticoagulant. An anticoagulant is a medication that prevents the clotting of blood. Warfarin is the generic term for the brand name drug Coumadin, by the way.

In brief, warfarin works like this. It stops the production of clotting factors dependent on vitamin K. In other words, vitamin K is an important player in the synthesis of various clotting factors and warfarin stops the synthesis of these factors.


Now you know enough to understand the possible interactions between vitamin K and warfarin. So let's get to them!

To better understand this interaction, let's pretend that the successful formation of a blood clot is equivalent to making a basketball shot. We have two teams, Team Warfarin and Team Vitamin K. They're playing against one another today. All Team Warfarin wants to do is stop Team Vitamin K from making the basket.

If the amount of warfarin in a person's body stays the same, but we increase our intake of Vitamin K, what's likely to happen? In our scenario, the number of players on Team Warfarin stays the same, but we increase the number of players on Team Vitamin K. Since there are more players on Vitamin K's team, will they have a better shot of making the basket now? Of course! Similarly, in the drug interaction that means when there's more vitamin K, a clot will be more likely to form.

Now let's say that the amount of warfarin in a person's body stays the same, but we decrease our intake of Vitamin K. What will be more likely to happen? Well, we've just slashed the number of players on the court for Team Vitamin K but kept the number of players for Team Warfarin the same. So will Team Vitamin K have a harder or easier time making the basket? They're outnumbered, so harder! That means a clot will be less likely to form. Or, in other words, a person is more likely to bleed out excessively if they get injured in this scenario.

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