Vitamin K can cause an interaction with blood thinners that you might be taking. Especially warfarin (Coumadin®). It's important that you are aware of which foods are high in vitamins K so your doctor can adjust your blood thinner dose correctly.

Vitamin K promotes the blood clotting process. You could think of it as a 'blood thickener'.

Warfarin, without going into too much detail, is trying to stop, or slow, that clotting process. So, warfarin is a ‘blood thinner’.

When you were started on warfarin your doctor generally orders labs that monitor how ‘effective’ the warfarin is on your blood. There are a number of different tests he can order. But, usually, he orders an 'INR'. This gives your doctor an idea of how fast your blood is clotting.

Here is the important part

Once your doctor decides to start you on warfarin it is very important that you tell him what kind of foods you are eating. And, that you continue to eat those same kinds of foods while you are on warfarin. Why?

Say that you don't eat a lot of leafy greens (which are generally high in vitamin K). So your doctor starts you on 2.5mg of warfarin a day. You get stabilized and everything is fine for a couple of weeks. But then you decide to go on a diet and you jump up your intake of salads and leafy greens.

This jump in vitamin K intake will start to 'thicken' up your blood - making it seem like your warfarin isn't as effective. So, unless your doctor knows of your dietary changes, he is going to start increasing your dose of warfarin to make your blood 'thinner'.

Then, if you suddenly stop the diet and cut back on the leafy greens, your blood will become too thin. You'll likely start seeing some bruising and maybe even more serious things that might require a trip to the hospital.

Now, it's likely that your doctor or pharmacist has already discussed this with you. But, the general rule of thumb is once you're started on warfarin you should continue with the same foods. Only introduce foods high in Vitamin K with your doctor's knowledge and permission.

Here's a table of the top vitamin K foods to help you:

Top Vitamin K Foods

1. Kale, frozen, cooked, boiled, drained, w/o salt 1,147 mcg
2. Kale, cooked, boiled, drained, without salt 1,062
3. 1 cup Collards, frozen, chopped, boiled, drained, wo/ salt 1,059
4. 1 cup Spinach, frozen, chopped , boiled, drained, wo/ salt 1,027
5. 1 cup Spinach, canned, drained solids 988
6. 1 cup Spinach, cooked, boiled, drained, without salt 889 1 cup Turnip greens, frozen, boiled, drained, wo/ salt 851
7. 1 cup Collards, cooked, boiled, drained, without salt 836
8. 1 cup Beet greens, cooked, boiled, drained, wo/ salt 697
9. 1 cup Turnip greens, cooked, boiled, drained, wo/ salt 529
10. 1 cup Mustard greens, cooked, boiled, drained, wo/ salt 419
11. 1 cup Brussels sprouts, frozen, boiled, drained, wo/ salt 300
12. 1 cup Broccoli, cooked, boiled, drained, without salt 220
13. 1 cup Brussels sprouts, cooked, boiled, drained, wo/ salt 219
14. 1 cup Onions, spring or scallions (includes tops, bulb), raw 207
    
15. 1 cup Dandelion greens, cooked, boiled, drained, wo/ salt 204
16. 1 cup Broccoli, frozen, chopped, boiled, drained, wo/ salt 183
17. 1 cup Spinach soufflé 172
18. 1 cup Asparagus, frozen, cooked, boiled, drained, wo/ salt 167
19. 1 head Sauerkraut, canned, solids and liquids 164
    
20. 10 sprigs Lettuce, iceberg (includes crisp head types), raw 116
21. 1 cup Endive, raw 100
22. 1 cup Lettuce, green leaf, raw 97
23. 1 cup Broccoli, raw 89
24. 1 head Okra, frozen, cooked, boiled, drained, wo/ salt 88
25. 1 cup Cabbage, cooked, boiled, drained, without salt 73
26. 1 cup Rhubarb, frozen, cooked, with sugar 71
27. 1 cup Okra, cooked, boiled, drained, without salt 64
28. 1 cup Cow peas, frozen, boiled, drained, wo/ salt 63
29. 1 cup Cabbage, Chinese (pak-choi), boiled, drained, wo/ salt 58
30. 1 cup Lettuce, cos or romaine, raw 57
31. 1 cup Celery, cooked, boiled, drained, without salt 57
32. 1 cup Broccoli, cooked, boiled, drained, without salt 52
33. 1 spear Cucumber, with peel, raw 49
34. 1 large Peas, edible-podded, frozen, boiled, drained, wo/ salt 48
35. 1 cup Spinach, raw 48
36. 1 leaf Cabbage, Savoy, raw 48
37. 1 cup Asparagus, frozen, cooked, boiled, drained, wo/ salt 48
38. 4 spears Cow peas, immature seeds, boiled, drained, wo/ salt 44
39. 1 cup Cabbage, raw 42