Harvard Heart Letter

Ask the doctor: Do people on warfarin need to avoid vitamin supplements that contain vitamin K?

Ask the doctor

Do people on warfarin need to avoid vitamin supplements that contain vitamin K?

Q. In your January issue you mentioned Centrum Cardio, a new multivitamin supplement that supposedly lowers cholesterol. Taking two tablets a day, as recommended, would deliver 25 micrograms of vitamin K. Is it wise to recommend this product for someone taking warfarin or other anticoagulants?

A. You raise an interesting point about vitamin K and its interaction with warfarin (Coumadin). This widely used drug prevents the formation of blood clots in the bloodstream by interfering with the way vitamin K helps produce clotting proteins. The more vitamin K in circulation, the more warfarin is needed to achieve a particular anti-clotting level.

It's a common misconception that people who take warfarin must avoid vitamin K, which is abundant in green, leafy vegetables such as kale, parsley, Brussels sprouts, broccoli, and collard, spinach, beet, and other greens. The body needs vitamin K to keep bones strong and healthy. There's also some evidence that vitamin K helps control calcification in blood vessels, an important step in atherosclerosis. What's important is keeping vitamin K intake consistent from day to day.

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