How does cooking affect vitamin K content?

Q. For foods that act as natural blood thinners (such as broccoli, cabbage, etc.), does it make a difference whether the foods are eaten raw or cooked? My mom, who takes prescription blood thinners, has been told that she should avoid all these foods. But these foods are also good for you and I would like to be able to find a balance. It seems to me that you would need to consume a great deal of vitamin K in order for it to produce a negative effect together with the Coumadin.

A. First, a clarification on why people taking blood-thinners are sometimes advised to avoid foods that are high in vitamin K. Vitamin K does not act as a natural blood-thinner; quite the opposite. Vitamin K regulates clotting action and can interfere with blood-thinning medication.

But you are quite right to note that these foods are also very good for you and, in fact, it is not necessary to eliminate them from the diet when taking blood-thinning medication.  It is important, however, to keep your intake of vitamin K relatively steady from day to day so that your doctor can calibrate your dosage appropriately. Please refer to this post for a more complete discussion of this issue.

To your question about how cooking affects vitamin K levels: The amount of vitamin K is not greatly affected by cooking.  Nonetheless, most vegetables are listed in our database in both their raw and cooked forms so you can check the vitamin K content of a food according to how its prepared.