Warfarin—brand name Coumadin®–is a blood thinner often prescribed for heart patients who are at risk for developing harmful blood clots. Sudden increases in vitamin K intake in your diet can decrease the effect of Coumadin. This is because vitamin K is an essential part of the chemical process for forming blood clots in your body.
Experts say you don’t need to completely avoid vitamin K if you are taking a blood thinner. It is an important nutrient in your diet. But if you are taking Coumadin or another blood thinner, you should not have large fluctuations day by day.
The recommended daily intake for vitamin K is 120 mcg for men and 90 mcg for women and should not be exceeded. The biggest source of vitamin K in our diet comes from leafy green vegetables.
Don’t ignore the labels
“Vitamin K foods can be included in your diet on a regular basis as long as you are mindful of the portion and keep the overall intake of vitamin K-rich foods consistent. For instance, you can choose to have a vitamin K rich food every day, every week, or three times in a week—as long as you keep this portion and frequency consistent,” explains Julia Zumpano, RD, LD, of Preventive Cardiology at Cleveland Clinic.
“If necessary, you can discuss including regular sources of vitamin K in your diet with your doctor in case your Coumadin dosage would need to be adjusted,” she adds. You will want to tell your physician how often you eat foods high in vitamin K and how much of those foods you eat. (Foods high in vitamin K are listed below.)
For veggie intake, there are a variety of vegetables that contain lower amounts of vitamin K. These include tomatoes, peppers, carrots, cauliflower, cucumbers, potatoes and sweet potatoes and squash (both summer and winter). Iceberg lettuce is low and romaine is also fairly low, so either can be eaten daily.
In addition, be sure to read labels on multivitamins as they have varying amounts of vitamin K. Talk to your doctor about what vitamins you should take.
Beware of herbal supplements and omega-3 supplements (EPA/DHA)
To keep your blood values stable, the following is recommended:
- Take your dose of Coumadin at the same time each day
- Have your blood values checked regularly (usually once per month with your physician; this may be more often during dose adjusting)
- From day to day, make sure your vitamin K intake is consistent
- Avoid certain supplements and vitamins
Limit to no more than 1 serving per day
| Food | Serving Size | Vitamin K (mcg) |
| 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 |
Limit to no more than 3 servings per day
| Food | Serving Size | Vitamin K (mcg) |
| 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 |
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