In order to understand the dietary recommendations for people taking Coumadin, it is important to first understand how the medication works. Blood clotting is a complex process that involves many different substances in the body, known as clotting factors, and several different steps. Coumadin works to inhibit blood clotting by decreasing the formation of active forms of certain clotting factors.
Some clotting factors require vitamin K to be converted into their active forms. Although this reaction changes vitamin K into an unusable form, the body can recycle it back using an enzyme known as vitamin K epoxide reductase. Coumadin blocks this enzyme, inhibiting the recycling of vitamin K and, thereby, decreasing the formation of the active clotting factors.
If a person taking Coumadin consumes much more vitamin K than he or she usually does, this will make the medication less effective, which could increase the risk of blood clots. Similarly, if he or she consumes less vitamin K, this could increase the effects of the drug, perhaps even causing a Coumadin overdose.
Once you understand how vitamin K affects Coumadin, it is easy to see that completely cutting out all foods high in vitamin K is not necessary and could even be dangerous, if you do so without your healthcare provider's supervision. Instead, you simply need to try to keep your vitamin K intake fairly consistent.
Green vegetables (especially dark green, leafy vegetables) are high in vitamin K. Various other foods contain vitamin K in varying amounts. If you are on vitamin K, your healthcare provider should give you a list of foods that are high in it.