Vitamin K is essential for good health and can prevent various diseases. But if you're on a blood thinner like warfarin, your doctor may recommend that you go on a low-vitamin K diet to prevent potentially serious interactions with the drug. It can be confusing to know which foods to eat and how much, but if you watch your diet carefully, you can still eat healthy foods while avoiding too much vitamin K.
Identification
Vitamin K was first discovered in 1929 by the Danish scientist Henrik Dam, who also noticed the nutrient's ability to affect blood clotting. There are two basic types of vitamin K: phylloquinones, made by plants, and menaquinones, made by bacteria. You get 90 percent of your dietary vitamin K from the phylloquinones from plant foods, with over half of those coming from vegetables, especially green leafy vegetables, according to World's Healthiest Foods website.
Effects
Vitamin K has been linked to the prevention and treatment of a wide variety of health conditions, including bone abnormalities, chronic liver disease, cystic fibrosis, cancer of the liver and pancreas, inflammatory bowel disease, kidney stones and bleeding. Of these, blood clotting is the most important as related to blood thinners and diet. Although you need enough blood clotting to help close skin wounds and prevent excessive bleeding, you don't want your blood to get so thick that it creates a clot in your blood vessels that can be fatal if it moves to your lungs, heart or brain. Vitamin K is one of the key nutrients for maintaining your blood-clotting ability in the right balance. Blood-clotting factors are measured as your international normalized ratio, or INR, with a low number meaning you have an increased chance for clotting and a higher number indicating a potential for bleeding.
Considerations
If you form a blood clot, you'll probably be placed on warfarin, the generic form of the brand-name drug Coumadin. Foods high in vitamin K can affect the ability of the drug to do its job and potentially lead to another clot. This doesn't mean you have to avoid all vitamin K foods, but the goal is to keep your vitamin K level stable, so the blood-thinning effects don't swing into a danger zone. The key is to eat approximately the same amounts each day, and then the dosage of your blood thinner can be adjusted as needed. With regard to cooking vegetables with vitamin K content, studies at the Nutrient Data Laboratory Beltsville, Maryland, showed that heating doesn't cause a major loss of vitamin K, and in some cases appears to increase the measurable amount of it. It's important to remember that for each increase in 100 mcg of vitamin K intake, your INR levels may be reduced by 0.2 percent, according to Ray Sahelian, MD, author of several books on diet and health.
Foods High in Vitamin K
Most of the foods that are very high in vitamin K are found in the green-leafy vegetable family, such as: spinach, Swiss chard, kale, collard greens, mustard greens, turnip greens, red-leaf lettuce, watercress, endive, cilantro, Bibb lettuce and white cabbage. Other foods with high levels include: green onions, green peppers, green peas, whole soybeans and canola oil. In addition to watching your intake of these foods, be aware that spices can also be sources of vitamin K, such as: dried basil, thyme, sage, coriander, oregano and marjoram -- although they would have to ingested in large amounts to have an effect on your INR.
Expert Insight
You should not avoid vitamin K foods altogether, especially if you have to take warfarin for life, since vitamin K has many health benefits. A study by Guylaine Ferland, et al, published in 2008 in the "Journal of the Federation of American Societies for Experimental Biology" found that a lifetime consumption of a low-vitamin K diet led to learning impairment in rats as they aged. Another report, from the long-term Framingham Study in Massachusetts, found that insufficient vitamin K can result in abnormal cartilage and bone mineralization and contribute to arthritis.
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