Jane Says: The Hidden Danger of Green Vegetables
“I have severe DVT [Deep Vein Thrombosis]. I am on blood thinner for life. I cannot eat greens or green food because the vitamin K interferes with my blood thinner. What can I do?”
—Cyndi Shelby Manka
I don’t ordinarily answer medical questions for one very good reason: I’m not a doctor. But March happens to be National DVT Awareness Month, and, besides, Cyndi’s question has haunted me ever since I read it last week. Greens are a cornerstone of my culinary repertoire, and I can’t imagine life without their extraordinary variety, nuances of flavor, and reservoirs of vitamins, minerals, and antioxidants.
DVT is the acronym for Deep Vein Thrombosis, a blood clot that forms in a vein deep in the body. It occurs most often in the lower leg or thigh, and the affected area may become swollen, red, and tender or painful. Ouch.
And it gets nastier. According to the National Heart, Lung, and Blood Institute at the National Institutes of Health (NIH), “A blood clot in a deep vein can break off and travel through the bloodstream. The loose clot is called an embolus. It can travel to an artery in the lungs and block blood flow. This condition is called pulmonary embolism.” And yep, it can (although not always) be as fatal as it sounds.
The (far from complete) list of risk factors for DVT includes slow blood flow, which may occur after surgery, if you’re laid up in bed for a long time due to illness or injury, or if you’re sitting still for more than four hours—on an airplane, for instance; some inherited conditions that increase the risk of blood clotting; birth control pills or hormone therapy; pregnancy and the first six weeks after giving birth; recent or ongoing cancer treatments; older age; and two that the NIH folks probably long to corral in a “Well, duh” category, obesity and smoking.
Now that I’ve scared the bejesus out of you, luckily, medical treatment with so-called “blood-thinning” drugs such as warfarin (the generic name for Coumadin) greatly reduce your blood’s ability to form a clot. I put the term in quotation marks because a blood thinner doesn’t actually thin the blood; in fact, it’s more properly called an anticoagulant.
And that brings us to vitamin K, which gets its name from the German Koagulationvitamin and is essential to the series of chemical reactions that cause blood clots to form. Warfarin works by decreasing the activity of vitamin K, so clotting proceeds at a slower rate.
Vitamin K is found primarily in green vegetables (including broccoli, brussels sprouts, cabbage, collards, dandelion greens, kale, spinach, turnip greens, and watercress), but also, surprisingly (to me, at any rate), in scallions, parsley, cauliflower, avocados, kiwifruits, grapes, and green tea.
If you are not taking an anticoagulant, eating foods packed with vitamin K will not—I repeat, will not—increase your risk of developing a blood clot. But if you ARE on an anticoagulant, then the more vitamin K you consume, the higher your dosage of the drug needs to be. Getting a balance between the two in your body is tricky, and the standard advice from doctors is to avoid vitamin K–rich foods altogether. This is a simple, effective approach, and one that’s hard to argue with.
However, sources such as The National Alliance for Thrombosis and Thrombophilia and the ClotCare Online Resource will tell you that you don’t have to completely avoid foods that are high in vitamin K, but instead, under the close supervision of your doctor, maintain a steady intake of it by adhering to a consistent diet. For example, if you plan to eat just one serving of a food high in vitamin K every day, then your doctor can monitor your blood-clotting time and adjust your prescription accordingly.
Whether you choose to closely control your consumption of foods rich in vitamin K or just cut them out of your diet, what will make your life easier is a list of foods and the amount of vitamin K they contain. One such list can be found on the website of “Dr. Gourmet,” a.k.a. New Orleans physician Timothy Harlan. In some cases, you’ll see he helpfully specifies amounts for the same vegetable in both raw and cooked forms. Take spinach, for instance. One cup of cooked spinach contains 888.5 micrograms (mcg) of vitamin K. That is the equivalent of about six cups of raw spinach (at 144.0 mcg per cup). Spinach salad, anyone?
A more comprehensive list, which reports the complete nutritional values of ingredients (including many prepared foods) and also differentiates between raw and cooked vegetables and fruits, can be found on the USDA National Nutrient Database. (Our tax dollars at work!) Vitamin K is listed at the bottom of the vitamins section; if it’s missing, relax—the vegetable or fruit that you are researching doesn't contain enough Vitamin K to be listed.
If you are on a blood thinner and decide you’d like to try working greens into your everyday routine, you have to promise me that you’ll have a confab with your doctor first, follow his or her instructions to the letter, and get your blood tested regularly.
If, on the other hand, you say goodbye to greens, know that there are plenty of other delicious, nutrient-packed vegetables under the sun. This summer, in fact, you can enjoy butter beans, beets, carrots, corn, cucumber (without the peel), eggplant, fennel, new potatoes, yellow summer squash, and tomatoes. Trust me, you won’t feel deprived.