Green, leafy vegetables contain vitamin K. Vitamin K does counteract warfarin. People who eat a lot of green, leafy vegetables may need a higher warfarin dose than people who do not eat as much. However, this is not necessarily bad.
Some studies have shown that people who consume fairly large amounts of vitamin K are able to better control their INRs. This is similar to the effect of entering a dark room and turning on a three-way light. The first increment of light seems a large change. The second increment may be the same change in wattage that the first increment was, but it appears smaller because the percentage change is smaller. Going from the second to the third increment appears to add little even though in absolute numbers the change is the same. However, the percentage is much smaller. Applying this to warfarin, the person who eats no green, leafy vegetables is greatly affected by even a small change. Whereas, the person who routinely consumes a fairly large amount of vitamin K is little affected by the same absolute amount of change.
In addition I do not believe that is wise to counsel someone who already has a health problem to avoid healthy foods.
Warfarin managers who tell people to avoid green, leafy vegetables are in effect saying to the consumer, ?Now look!! I have chosen the correct warfarin dose for you and it is your duty to take whatever measures are necessary to prove me right.?
My philosophy of warfarin management is to say, ?Eat a healthy diet and I will simply adjust your warfarin dose to fit your lifestyle.?
In addition, Dr. Fernstrom used the term ?blood thinner?. This seriously calls into question her understanding of warfarin. Warfarin is not able to lower the viscosity of the blood. Instead, it slows the formation of clots. The term blood thinner is archaic. It dates from the 1950s when President Eisenhower was given warfarin. In those days they had no technology to determine how most medications worked. All they knew was that when someone taking warfarin got cut, they bled longer. The logical conclusion in those low-tech days was that the blood was thinner.
When someone presents themselves as an expert and uses the term ?blood thinner? you have to be very suspicious that their level of understanding of warfarin is rudimentary.