How can spinach and goat cheese salad or grilled asparagus affect your blood? It all starts with coagulation. Coagulation or blood clotting is the critical process that prevents blood loss after any type of blood vessel damage. Vitamin K is essential to this blood clotting process. However, coagulation can happen too quickly or even without injury. In these circumstances, an anticoagulant or blood thinner medication may be prescribed to reduce the formation of blood clots. Since vitamin K affects blood clotting, it can interfere with blood thinners and require monitoring of your intake of high vitamin K foods.
Vitamin K is a fat-soluble vitamin, meaning it is stored in the fat tissues and liver. There are two forms of vitamin K, vitamin K-1 and vitamin K-2. Vitamin K-1 is the principal dietary form found in plant sources such as leafy green vegetables. Vitamin K-2 is found in animal sources and is also made by colonic intestinal bacteria. During the blood-clotting process, referred to as the coagulation cascade, a clot is formed with the help of blood-clotting enzymes. Vitamin K is needed for activation of these enzymes.
Vitamin K and Anticoagulant Interaction
Anticoagulant blood thinners interfere with the blood-clotting process by blocking vitamin K function. Without vitamin K, the coagulation cascade will not occur as quickly, lengthening the time it takes to form a blood clot. The International Normalized Ratio, INR, is a laboratory test that measures the time it takes for blood to clot. Blood thinners prolong clotting time, resulting in a longer INR. A substantial change in consumption of vitamin K food sources can cause a significant change in INR. For example, if you eat 3 servings of vitamin K foods one day and none the next, it can cause large fluctuations in the INR and make it more difficult to manage your blood thinner medication.
Vitamin K Food Sources
Intake of high and moderate vitamin K food sources must be monitored for effective blood thinner therapy. Foods considered high in vitamin K contain more than 100 micrograms per serving. These foods include 1 cup fresh or 1/2 cup cooked kale, spinach, collard greens, Swiss chard, mustard greens, watercress, parsley, Brussels sprouts, green tea and green onions. Moderate vitamin K foods contain 11 to 99 micrograms per serving and include broccoli, cauliflower, avocado, lettuce and cabbage. Certain vegetable oils, such as soybean, cottonseed, canola and olive oil, are also moderate in vitamin K. Foods with less than 10 micrograms per serving of vitamin K, such as meat, dairy products, eggs, most fruits, grains and legumes, are low in vitamin K.
The vitamin K recommended daily allowance is 120 micrograms for adult men and 90 micrograms for adult women. When taking anticoagulants, do not eat more than the RDA each day and keep vitamin K intake consistent. Significant changes to vitamin K intake can make it harder to determine the best medication dosage for you. For example, you can choose to eat two servings of vitamin K-rich foods, as long as you eat two servings most days. If you enjoy vitamin K foods, you can eat more as long as you eat the same amount daily and don't exceed the RDA. Any dietary changes that effect vitamin K intake should be communicated to a health-care provider.
- National Institute of Health: Coumadin and Vitamin K
- Linus Pauling Institute: Vitamin K
- Journal of Agricultural and Food Chemistry: Vitamin K Contents of Meat, Dairy, and Fast Food in the U.S. Diet
- National Alliance for Thrombosis and Thrombophilia: Vitamin K and Warfarin
- University of Utah Health Care: Vitamin K Content of Common Foods
- The Institute of Medicine: Dietary Reference Intakes
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