Dr. Tim Says....

What is the Right Dose of Vitamin K?

I get the question all the time about how much Vitamin K is right for folks taking Coumadin® (warfarin). Unfortunately, there's no perfect study to guide just how much Vitamin K is too much for those taking Coumadin. Most physicians recommend limiting foods that contain very high or even moderate amounts of Vitamin K. At the same time, there's never been a recommendation to severely limit Vitamin K intake.

The Recommended Daily Allowance (RDA) for Vitamin K is 80 micrograms (mcg) for males and 70 mcg for females. The majority of ingredients contain small amounts - in the under 15 mcg range - so keeping an eye on foods that contain more than 20 - 25 mcg per serving is a good rule of thumb.

Avoiding all Vitamin K might be just as much of a problem as getting too much, however. Studies have clearly shown that eating foods that are higher in Vitamin K will have an effect on the effectiveness of Coumadin and the INR. Most people who either take warfarin themselves or those who help patients manage their anti-coagulation know this, but there is some research now that shows eating too little Vitamin K can have the same effect.

So what to do? How much is too much? How little is too little? It appears, from what research we have, that in those folks who were taking Coumadin, 29 mcg was too little and 76 mcg just right to keep their INR stable.

While it's not a perfect way to look at the issue of how much is too much Vitamin K in the diet for warfarin users, another study showed an effect on the INR in those taking 150 - 200 mcg per day in Vitamin K supplements. These are the levels found in Vitamin K rich foods such as spinach, collard greens, and broccoli.

For the number of folks who use this medication, it is a shame that a large study has not been done to help answer this question more clearly. For the time being, we have to be content with the small studies that point toward an optimum near the RDA guidelines for Vitamin K.

There are three lists on the website based on increasing levels of detail about the Vitamin K content of foods.

Brief : A short list of commonly-used foods with their relative Vitamin K levels (Low, Medium, High)
Medium : A much longer list of foods, with their relative Vitamin K levels (Low, Medium, High)
Extensive : The same longer list as the Medium document, but with exact levels of Vitamin K in mcgs.

In addition, the handy paperback Vitamin K Levels in Common Foods is the most comprehensive listing available, with over 800 common ingredients listed both alphabetically and in decreasing Vitamin K amount.

Use these lists to help you keep your daily intake in a consistent, healthy range.

Eat well, eat healthy, enjoy life!

Timothy S. Harlan, MD, FACP, CCMS
Dr. Gourmet