by Catherine Britell, M.D.
One sunny summer afternoon about 15 years ago, my husband and I were enjoying a double kayak paddle in Seattle’s Lake Union, looking at the houseboats and ducks and conjecturing about the “Sleepless in Seattle” lifestyle, when he suddenly said, “Cathy, you need to paddle us back to the rental place now.” So, I did, and then he said, “Now you need to drive us to the hospital. I’m not feeling well”. And the next day, he had a brand new plastic heart valve to replace the congenitally malformed one that had suddenly started malfunctioning.
In order to prevent formation of blood clots on the artificial valve, it’s necessary for him to take a warfarin anticoagulant. Others need to take anticoagulant medications for other reasons. The dose of this medication needs to be carefully adjusted according to regular blood tests.
Why is this relevant to SANE eating? It’s important because blood clots are formed through a series of chemical reactions in your body, and Vitamin K is necessary for many of those reactions. Warfarin (brand name: Coumadin) works by decreasing the activity of Vitamin K; lengthening the time it takes for a clot to form. And Vitamin K is found in very high to moderate amounts in many of the non-starchy vegetables that are the mainstay of SANE eating. For us, it means that we pay attention to the Vitamin K in our foods, and for my husband, a slightly larger daily dose of anticoagulant medication.
The International Normalized Ratio (INR) and the Prothrombin Time (PT) are determined by the time it takes blood to clot. Individuals at risk for developing blood clots take warfarin to lengthen the usual time it takes for a clot to form, resulting in a prolonged INR/PT. Doctors usually measure the INR/PT every month in patients taking warfarin to make sure it stays in the desired range.
So, if you’re taking warfarin anticoagulants, it’s important to keep your vitamin K intake as constant as possible. Sudden increases in vitamin K intake may decrease the effect of the medication, while lowering your vitamin K intake could increase the effect of warfarin. It’s important, then, to keep your intake of foods rich in vitamin K about the same each day. For example, you may plan to eat only ½ cup of these foods per day. If you like these foods and eat them often, you can eat more, but be consistent. Some people find that VERY large quantities of high Vitamin K vegetables may make it difficult to achieve and maintain therapeutic anticoagulation and so may wish to go easy on kale, spinach, and collard greens.
If you are taking warfarin anticoagulants it’s vital that you know the vitamin K levels in various non-starchy vegetables, so that you can maintain the desired consistency in intake. Here’s a list of foods highest in Vitamin K.
Food Serving Size and Vitamin K levels (micrograms)
- Kale, cooked 1/2 cup — 531
- Spinach, cooked 1/2 cup — 444
- Collards, cooked 1/2 cup — 418
- Swiss chard, raw 1 cup — 299
- Swiss chard, cooked 1/2 cup — 287
- Mustard greens, raw 1 cup — 279
- Turnip greens, cooked 1/2 cup — 265
- Parsley, raw 1/4 cup — 246
- Broccoli, cooked 1 cup — 220
- Brussels sprouts, cooked 1 cup — 219
- Mustard greens, cooked 1/2 cup — 210
- Collards, raw 1 cup — 184
- Spinach, raw 1 cup — 145
- Turnip greens, raw 1 cup — 138
- Endive, raw 1 cup — 116
- Broccoli, raw 1 cup — 89
- Cabbage, cooked 1/2 cup — 82
- Green leaf lettuce 1 cup — 71
- Prunes, stewed 1 cup — 65
- Romaine lettuce, raw 1 cup — 57
- Asparagus 4 spears — 48
- Avocado 1 cup (cube, slice, puree) — 30-48
- Tuna, canned in oil 3 ounces — 37
- Blue/black-berries, raw 1 cup — 29
- Peas, cooked 1/2 cup — 21
The bottom line: If you’re taking anticoagulant medications, eating a SANE diet with abundant non-starchy vegetables will be wonderful and healthy for you. However, when you embark upon your SANE lifestyle, even when you are choosing low or moderate Vitamin K vegetables, you can expect your warfarin dose to increase, just because of the number of servings of vegetables you are now eating. And you’ll probably need to have more frequent blood tests for awhile. So, it’s important to
- let your doctor know that you’re eating significantly more vegetables
- follow his/her instructions as regards monitoring and warfarin dosage
- keep your Vitamin K intake moderate and steady.