A drug's effectiveness is often determined by the foods you eat. The interaction between Coumadin, a blood thinner, and vitamin K is one example. Serious health problems may occur when the drug mechanism is altered. Understanding the role of vitamin K in blood clot formation, its food sources and how to manage vitamin K intake along with Coumadin therapy is essential in preventing undesirable complications.
Vitamin K
Vitamin K occurs naturally in two forms, phylloquinone and menaquinone. Phylloquinone is synthesized in plants and is the main dietary source of the vitamin. Menaquinone is produced by bacteria. The body requires the presence of bile and pancreatic juices to absorb phylloquinone. Adding fat to a vitamin K-rich food, such as olive oil to spinach, will aid absorption. After absorption, vitamin K is transported to the liver via the bloodstream. The liver is the site where blood clotting factors are made. There are seven vitamin K-dependent proteins necessary for blood clotting. Prothrombin, factors VII, IX and X are the primary ones. Additionally, vitamin K seems to be involved with bone and vascular health.
Coumadin
Coumadin is the brand name of the medication warfarin. The drug works by decreasing the activity of vitamin K and lengthening the time it takes for a blood clot to form. Physicians measure the effectiveness of the Coumadin using blood tests, which monitor Prothrombin Time (PT) and the International Normalized Ratio (INR). Target PT/INR values are individualized according to your health condition and response to the drug. Keeping the PT/INR stable is key to proper management. This is accomplished by taking the exact dose of Coumadin prescribed at the same time each day and keeping vitamin K intake consistent.
Food Sources
Green leafy vegetables are the best source of vitamin K. This includes kale, spinach, turnip greens, Swiss chard and collard greens. Moderately high amounts are found in brussel sprouts, broccoli and lettuces such as leaf, endive and romaine. Smaller amounts are contained in asparagus, red cabbage, avocados, liver and soybean oil. Cooking has no effect on the absorption of the vitamin in the body.
Intake levels
The Food and Nutrition Board of the National Academy of Sciences recommend that the adequate intake (AI) for vitamin K is 120 mcg for men and 90 mcg for women each day. Pregnant and lactating women require 90 mcg also. No upper limit of tolerance is established. The average American adult consumes between 70 to 80 mcg of vitamin K each day. Intakes may be higher during summer months when produce is abundant.
Considerations
According to the 2010 Physician's Desk Reference, herbal products, dietary supplements and alcohol also interact with Coumadin. Alcohol intakes greater than three drinks per day can increase the drug's effects. Most physicians suggest avoiding all alcoholic drinks while on Coumadin therapy. Numerous dietary supplements known to interfere with PT/INR readings and include arnica, cat's claw, cranberries, dong quai, bilberry, butchers broom, horse chestnut, feverfew, licorice, turmeric, vitamin E, woodruff, St. John's wort, red clover, pau d'arco, forskolin, garlic ginger, ginko, wheat grass and willow bark. Consult your physician or pharmacist if you are taking any supplements for further recommendations.
References
- "Journal of the American Dietetic Association"; Vitamin K: What are the Current Dietary Recommendations for Patients Taking Coumadin; Sharon Denny, et al.; 2007
- PubMed Health; Warfarin; Sept. 2008
- 2010 Physician's Desk Reference for Consumers
- Institutes of Medicine; Dietary Reference Intakes; 2010
- MayoClinic.com; Warfarin Side Effects: Watch for Dangerous Interactions; Jan. 2010
