DEAR DR. BLONZ: I am physically active and eat well, including lots of vegetables. After I tore a muscle in an athletic injury, a blood clot developed in my calf. My doctor put me on warfarin, an anticoagulant, explaining that it needed to be that particular drug because of another medication I take.
I just started it, and have to be carefully monitored with weekly blood tests. My question relates to one of the most important directives -- namely, that I monitor my intake of vitamin K. Can you tell me what foods contain a significant amount of vitamin K? -- M.P., Berkeley, California
DEAR M.P.: Blood clotting, also known as coagulation, is a multistep process. Medications known as anticoagulants, or blood thinners, help prolong clotting time. (Interestingly, leeches, mosquitos and other insects and animals that feed on blood make their own anticoagulants to facilitate their ability to dine at our expense.) Your doctor is taking special steps to ensure that your blood doesn't clot in the wrong places in the future, and to facilitate your ability to break down the existing unwanted clot before it causes problems.
As you note with your weekly blood tests, the body's clotting tendency needs to be carefully monitored in such cases; the goal is to slow it down, not eliminate it entirely.
Vitamin K is an essential nutrient needed for its involvement in the blood-clotting process. Vitamin K comes in two forms that work in our body: Phylloquinone is found in foods, while menaquinone gets produced by friendly bacteria in the large intestine. (Note that those taking antibiotics for extended periods could be at risk for a vitamin K deficiency, as these drugs can destroy the intestinal bacteria that would normally make menaquinone.) Warfarin, also known by its brand name Coumadin, is what's referred to as a vitamin K antagonist: It reduces clotting by interfering with vitamin K's clot-promoting function.
The recommended adequate intake of vitamin K for adult women is 90 micrograms per day, and for men, it is 120 micrograms per day. Foods rich in vitamin K include turnip greens, kale, spinach, Brussels sprouts, soybeans, lettuce, cabbage, cauliflower, lentils, broccoli and beef liver. Lesser amounts are also found in chickpeas, eggs, strawberries and nonfat milk. It is often present in multivitamins, so check all supplement labels.
Make it a goal to keep your vitamin K intake fairly constant from day to day. You also should avoid making changes to your intake of vitamin E, garlic, alcohol and aspirin, as these can decrease blood-clotting tendency. Certain herbal supplements also contain natural blood thinners. Periodic blood tests are designed to verify that things remain in sync throughout the treatment.
I encourage you to discuss all these topics thoroughly with your physician, the hematologist on the team, a registered dietitian and/or your pharmacist.
Check b.link/8tqa3c for general information about vitamin K. For a brief National Library of Medicine video describing clotting in action, see b.link/zm65tg. Finally, for information about anticoagulant medications, check b.link/5tzsnt; this page includes special considerations for those using warfarin.
Send questions to: "On Nutrition," Ed Blonz, c/o Andrews McMeel Syndication, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to questions@blonz.com. Due to the volume of mail, personal replies cannot be provided.