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Consistency, Not Avoidance: The Truth About Blood Thinners, Leafy Greens, And Vitamin K

If you take blood thinners, chances are you've heard that certain foods—like leafy greens—can cause potentially dangerous food-drug interactions.Blood thinners quote

"I get a lot of patients who come to me and say, 'I was told to avoid these foods because they interfere with my medication'," says Fran Burke MS, RD, a clinical dietitian in the Preventive Cardiovascular Program at Penn Medicine. "But the issue isn't avoidance, it's consistency."

Questions and Answers with a Clinical Dietitian

Here are 4 questions and answers about blood thinners and foods rich in vitamin K:

Who takes blood thinners—and why?

Patients are placed on blood thinners for a variety of medical conditions, including atrial fibrillation (A-Fib).

In A-Fib, blood isn't properly pumped out of the heart, which can cause clots to form. The blood clots can then dislodge from the heart and cause a type of stroke called ischemic stroke.

"People who have A-Fib are at risk of having a stroke, so they're put on blood thinners to prevent blood clots," explains Fran.

Download Penn A-Fib Guide

How do blood thinners interact with Vitamin K?

The body uses vitamin K to help clot blood, explains the National Library of Medicine (NLM). Because people with A-Fib are at risk for clots in the heart, vitamin K has important implications.

Warfarin (the generic version of Coumadin) is the most widely used blood thinner that works by blocking a vitamin K-dependent step in clotting factor production.

This is why consistency in vitamin K intake is important: Your body needs to keep a balance between the amounts of vitamin K and warfarin in your system.

However, not all blood thinners interact with vitamin K, so ask your physician about your specific medication.

"The new anticoagulation agents include Rivaroxaban (Xarelto), Dabigatran (Pradaxa), and Apixaban (Eliquis). These agents have no food-drug interactions and therefore do not interact with vitamin K," explains Fran.

Foods high in vitamin K

How can you keep Vitamin K levels consistent?

"What you should try to do is keep your intake of foods rich in vitamin K about the same each day," says Fran. "For example, if you eat one serving of broccoli on one day, you should plan on eating one serving of a high vitamin K food the next and so on. One serving a day, several days a week would help to keep your vitamin K intake consistent."

Fran explains that the adequate intake (AI) for vitamin K for men and women who are 19 or more years old is 120 mcg and 90 mcg, respectively. A cup of raw spinach contains about 145 mcg of vitamin K, whereas 1 cup of cooked broccoli contains about 220 mcg of vitamin K.

How are patients who take blood thinners monitored?

Warfarin doses need to be monitored closely. Patients can go to an outpatient warfarin clinic where they are monitored—initially once a week for about one month, then every two weeks, and finally once a month.

The main blood test used to monitor patients on warfarin is called prothrombin time (PT). A PT test measures how long it takes for plasma (the liquid portion of your blood) to clot, says the NLM.

The result is often listed as a number called an international normalized ratio (INR). People who are not on blood thinners should have an INR between 0.8 and 1.1, according to the NLM. People who are on warfarin should be between 2.0 and 3.0 for most conditions.

If you are on blood thinners, the key to minimizing food and drug interactions is through consistency, not avoidance. Eating a steady amount of vitamin K rich foods each day helps ensure a healthy, well-balanced body.

A physician at Penn Medicine's Cardiac Arrhythmia Program can help you determine the best course of action to keep your vitamin K and blood thinner levels balanced.

About this Blog

The Penn Heart and Vascular blog provides the latest information on heart disease prevention, nutrition and breakthroughs in cardiovascular care.


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