Vitamin K Foods That Interfere With Coumadin
The drug Coumadin (also known as warfarin) is prescribed to people who have an increased risk of developing blood clots. It's important to keep tabs on your vitamin K intake when taking Coumadin on a daily basis. Eating too many foods that contain a large amount of vitamin K can seriously affect the medication. The majority of vitamin-K-rich foods are green vegetables.
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Relationship
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Vitamin K plays an essential role in the formation of blood clots in the body. When a person has a clotting disorder, this means that the clotting process feeds off of vitamin K to work overtime. Clots form quickly and can be life-threatening when this is the case. Coumadin decreases the effectiveness of vitamin K, which increases the amount of time clots take to form. Because Coumadin slows the speed at which blood clots form by attacking vitamin K, it's important to keep tabs on how much vitamin K you're ingesting each day. Taking in a larger amount of vitamin K than usual can decrease the effectiveness of Coumadin.
Concentrated Sources
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Concentrated sources of vitamin K are most likely to interact with Coumadin, and, therefore, must be the most severely limited. Kale, spinach, Swiss chard, collard greens, turnip greens, mustard greens and parsley all fall into this category. It's best to limit intake of these highly concentrated sources of vitamin K to one serving per day: either 1/2 cup of cooked greens or 1/4 cup of raw parsley.
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Moderate Sources
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Moderate sources of vitamin K are less likely to affect Coumadin severely, but should still be monitored daily. Items such as cooked Brussels sprouts, raw broccoli, raw endive and romaine and green-leaf lettuces are all moderate sources of vitamin K. Raw spinach and raw turnip greens are also included in this group, as they are less concentrated than their cooked counterpart. Coumadin users should consume no more than three servings per day of these foods. A serving is equivalent to 1 cup of the raw vegetables or 1/2 cup of the cooked Brussels sprouts.
Low Sources
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Some foods contain vitamin K, but are so low in the nutrient that they pose no real threat to Coumadin. Iceberg lettuce, red cabbage, soybean oil and asparagus all contain measurable amounts of vitamin K. However, they are not as highly concentrated as the items in the first two groups, and it would take far more servings of them to affect Coumadin in the same way. Therefore, there are no serving limits on foods in this category.
Warning
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Because Coumadin extends the amount of time that it takes blood clots to form, doctors must monitor patients taking this drug carefully. Through once-monthly blood tests, doctors measure patients' Internal Normalized Ratio (INR) and Prothrombin Time (PT). These tests monitor the amount of time it takes clots to form in the blood. Based on the test results, doctors can adjust the medication dosage as needed. Limiting foods that are heavy on vitamin K is key to having normal INR and PT readings. As long as you keep your daily vitamin K intake consistent, the doctor can easily determine the correct amount of Coumadin to prescribe. If that intake is not consistent, it can be difficult to regulate clotting with medication.
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