Vitamin K in Foods
Medically reviewed by Drugs.com. Last updated on Apr 2, 2024.
What do I need to know about warfarin and vitamin K?
- Warfarin is a type of medicine called a blood thinner. It makes your blood clot more slowly. This can help prevent dangerous problems, such as a stroke (a blood clot in the brain). Vitamin K helps your blood to clot (thicken to stop bleeding). Warfarin works by making it harder for your body to use vitamin K to clot blood. Changes in the amount of vitamin K that you normally eat can affect how warfarin works.
- Your healthcare provider can tell how well warfarin is working from a blood test that you will have regularly. This test is called an international normalized ratio (INR). It shows how quickly your blood clots. To keep your INR at a healthy level, you need to manage how much vitamin K you eat.
How much vitamin K should I eat while I take warfarin?
Eat the same amount of vitamin K each day. Do not change the amount of vitamin K you normally have from foods or supplements. This helps keep your INR at the same healthy level.
- A big increase in vitamin K can lower your INR. This can cause dangerous clotting in your blood.
- A big decrease in vitamin K can raise your INR. This can make it harder for your blood to clot. It can cause you to bleed too much. Do not avoid foods that contain vitamin K.
Which foods have vitamin K?
Dark green leafy vegetables have the highest amounts of vitamin K. Foods that contain vitamin K include the following:
- Foods with more than 100 mcg per serving:
- ½ cup of cooked kale (531 mcg)
- ½ cup of cooked spinach (444 mcg)
- ½ cup of cooked collard greens (418 mcg)
- 1 cup of cooked broccoli (220 mcg)
- 1 cup of cooked brussels sprouts (219 mcg)
- 1 cup of raw collard greens (184 mcg)
- 1 cup of raw spinach (145 mcg)
- 1 cup of raw endive (116 mcg)
- Foods with 50 to 100 mcg per serving:
- 1 cup of raw broccoli (89 mcg)
- ½ cup of cooked cabbage (82 mcg)
- 1 cup of green leaf lettuce (71 mcg)
- 1 cup of romaine lettuce (57 mcg)
- Foods with 15 to 50 mcg per serving:
- 4 spears of asparagus (48 mcg)
- 1 medium kiwi fruit (31 mcg)
- 1 cup of raw blackberries or blueberries (29 mcg)
- 1 cup of red or green grapes (23 mcg)
- ½ cup of cooked peas (19 mcg)
What are other sources of vitamin K?
Multivitamins and other supplements may contain 10 to 80 mcg of vitamin K. These amounts can cause changes in your INR. Read the labels of any supplements you take. Do not take more than 1 supplement that contains vitamin K. Talk to your healthcare provider about the supplements you are taking.
When should I contact my healthcare provider?
- You have a poor appetite.
- You have an upset stomach.
- You have hair loss.
- You bruise more easily than normal.
- You have questions about your medicines, supplements, or the amount of vitamin K you eat.
When should I seek immediate care?
- You cough up blood.
- You have red or black bowel movements.
- Your urine is red or dark brown.
- You have bleeding from your gums or nose.
- You have heavy bleeding from a wound that does not stop, or unusually heavy monthly periods.
- You have a severe headache.
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