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Vitamin K & Warfarin

What is Vitamin K?

Vitamin K is a fat soluble vitamin that is responsible for the maintenance of normal blood coagulation in the body. Use of anticoagulation medication such as Warfarin, can affect your Vitamin K requirements.

What is Warfarin?

Warfarin (sold under the names of Coumadin and Marevan) is an anticoagulant or most commonly referred to as ‘blood thinning’ medication. Warfarin is prescribed for those who have blood clots such as Deep Vein Thrombosis or Pulmonary Embolism. It is also used in the prevention of stroke in people with Atrial Fibrillation, Valvular Heart Heart Disease or those who have had surgery on the valves in their heart.

Warfarin Testing

Through a blood test, your doctor is able to tell how well Warfarin is working by checking your International Normalized Ratio (INR) that measures the rate at which a blood clot forms. There are a number of factors that can affect your INR.

To make sure your medication works effectively, it is important to monitor your dietary intake of foods containing Vitamin K and ensure your intake is consistent. A large increase in Vitamin K consumption can lower your INR and therefore result in dangerous clotting of your blood. On the other hand, a large decrease in consumption of Vitamin K can raise your INR and make it difficult for your blood to clot, leading to too much bleeding.

How do I manage my intake?

For those prescribed Warfarin, it is not necessary to completely eliminate Vitamin K containing foods from your diet. It is important, however, that you eat foods containing moderate or high amounts of Vitamin K consistently.

Here is a list of foods containing Vitamin K. You can either choose to consume those very high in Vitamin K or consume those high in Vitamin K or moderate amounts of Vitamin K. Whatever you choose, just ensure that it is consistent.

Foods containing VERY HIGH Vitamin K content (400-800µ/100g)

1 – 2 tablespoons per day of cooked:

  • Beet greens, mustard greens, turnip greens
  • Collards
  • Kale
  • Parsley (raw: tabouli)
  • Pesto (based on basil and other herbs)
  • Spinach
  • Swiss Chard
  • Silverbeet

Foods containing HIGH Vitamin K content (100-200µ/100g)

¼ – ½ cup per day cooked

  • Asian greens
  • Broccoli
  • Brussel sprouts
  • Spring onion

Foods containing MODERATE Vitamin K content (30-100µ/100g)

½ – 1 cup per day cooked

  • Asparagus
  • Cabbage and saurerkraut
  • Coleslaw (raw)
  • Endive (raw)
  • Dark leafy lettuce
  • Okra

It is also important that you try to include at least 3-4 serves per day of other vegetables where 1 serve is equal to ½ cup cooked vegetables, 1 cup of salad vegetables and 1 small potato. Examples include:

  • Capsicum
  • Carrot
  • Cauliflower
  • Celery
  • Green beans
  • Cucumber
  • Peas
  • Iceburg lettuce
  • Mushrooms
  • Parsnip
  • Potato
  • Pumpking
  • Corn
  • Sweet potato
  • Tomato
  • Zucchini

Keeping your INR Stable

To keep your INR stable it is recommended you:

  • Take your medication exactly as your doctor prescribed
  • Have your INR checked regularly
  • Keep your Vitamin K intake consistent

Other Interactions

When you are taking a medication, particularly Warfarin, it is important that you know any interactions the medication may have with other factors such as specific foods.

There a few other interactions that you need to be aware of including:

Specific food interactions

  • There have been occasional reports of changes in INR when people have consumed large of amounts of foods including avocado, mango, soy drinks, matcha green tea, cranberry and grapefruit
  • Drinking up to 1 cup (250ml) of cranberry juice or soy milk is unlikely to affect your INR though
  • Other food interactions may be possible, so it is best just to consume a variety of foods and avoid excessive amounts of one food.

Weight loss diets

  • It is important that you work closely with your doctor and are monitored regularl
  • If you are planning on starting a weight loss diet, it is important to let your doctor know as specific diets such as hgih protein, low carbohydrate diets induce changes with your INR
  • Avoid fasting, binge eating and crash diets as this will change your warfarin dosage
  • It is best to talk to a Dietitian if you plan on starting a special diet


  • When consumed in large amounts, alcohol can have variable interactions with Warfarin
  • It is important to only drink in moderation and do not partake in binge drinking
  • For general health, the Australian Alcohol Guidelines recommended consuming no more than two standard drinks in a sitting with at least two alcohol free days per week
  • Many supplements and herbs can interact with warfarin and change your INR
  • If you take a multivitamin that contains Vitamin K, make sure you take it consistently everyday
  • Herbal supplements including Co-Q 10, Gingko Biloba, Ginseng and Garlic interact with Warfarin
  • Chinese Herbs such as Dong Quai and Dan Shen also interact with Warfarin
  • It is important you consult with your Doctor before starting any supplement

In Conclusion

Warfarin can be a life saving medication but it is also one that we must exercise a large amount of caution with.

At Exact Physiology we recommend that if you are taking a medication such as Warfarin that you make an appointment with one of our accredited dietitians.

*Adapted from DAA Food and Warfarin resource

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