Blood Thinners and Greens: A Mix to Avoid?

12 September, 2016 , ,

You might have heard that if you take an anticoagulant (blood thinner), like Coumadin (warfarin), you should stop eating, or at least eat fewer, green vegetables, because they contain too much Vitamin K. But is this really the case?

Before getting right into the topic, let’s review some basics. Firstly, it’s important to note that Coumadin (generic name: warfarin) is an anticoagulant, which means it stops the formation of blood clots and makes blood thinner (less viscous). As for Vitamin K, it helps the process of blood clotting. In other words, warfarin has the opposite effect to Vitamin K.

What is INR (International Normalized Ratio)? And how does it vary?

The INR is a test used by doctors and pharmacists to check the effectiveness of blood thinning medication (Coumadin/warfarin) and to adapt the dosage. Ideally, you should maintain as stable an INR as possible, meaning you should maintain an optimal blood coagulation rate.

Several factors can influence and unbalance this rate, the seven main ones are:

  • Travelling
  • Moving home
  • Depression
  • Divorce
  • Bereavement
  • Malnutrition
  • Dementia

Other factors include genetics, diet, adherence to treatment and other medications you may be taking. Natural supplements are included in the list of medicines that can affect INR.

Natural Supplements and Anticoagulation Therapy


For your information, here are a few examples of natural products that could influence your INR more than eating green vegetables:

  • Those which increase INR values:
    • Boldo and fenugreek
    • Cranberry juice (in large quantities)
    • Danshen
    • Devil’s Claw
    • Dong Quai
    • Garlic capsules
    • Ginger
    • Ginko biloba
    • Mayweed
    • Papain
    • Vitamin E (in doses larger than 400 units/day)
  • Those which reduce INR values:
    • Coenzyme Q10
    • Ginseng
    • Green tea (in large quantities)
    • St. John’s Wort

Always speak to your pharmacist before you start or stop taking a supplement. If you take supplements, make sure you tell your doctor and your pharmacist.

Now that we’re reviewed some basic facts, let’s get to the nitty gritty: diet and its effect on medication! Several vegetables, particularly green ones, contain Vitamin K, in varying quantities. As mentioned earlier, warfarin (Coumadin) is a Vitamin K antagonist. Its presence or absence from the diet can play a role in the medication’s effectiveness.

Why You Shouldn’t Avoid Green Vegetables

food basket, paniel d'aliments

Two main reasons can explain why reducing your intake of green vegetables is not necessary, even if you’re going through anticoagulation therapy.

Firstly, despite what you might have heard, the presence of Vitamin K in the diet helps better balance your INR. Indeed, regularly eating vegetables, particularly green ones, helps you to be less sensitive to daily variations in Vitamin K. This is explained by the fact the liver stocks some Vitamin K, because it is a fat soluble vitamin.

For example, if you eat green vegetables every day, your liver stores Vitamin K. If, one day, you have a lower intake of Vitamin K, this will have practically no repercussions. Vitamin K stored in the liver will be used. This way, you can maintain you INR as stable as possible. However, if you never eat green vegetables, you don’t have Vitamin K stores, so if you eat a good amount of green vegetables one day, you’ll experience a “peak” of Vitamin K, which will then destabilize your INR.

Secondly, Vitamin K’s bioavailability depends on several factors like cultivation, storage and cooking of foods. What’s more, we only know the Vitamin K content of around half the food in the North American diet. It’s therefore practically impossible to establish and respect a recommended daily intake of Vitamin K.

For these reasons, we recommend an intake of 1 to 2 portions of green vegetables each day, even for those taking Coumadin. This quantity enables you to have a better control of your medication and to meet the nutritional needs established by Health Canada. What’s more, green vegetables are great for health!

Note: if you are a fan of Asian cuisine and regularly eat natto (a traditional Japanese food made from fermented soya beans), it would be a good idea to avoid it, because it contains a large quantity of Vitamin K (much higher than what is commonly found in vegetables), which can influence your INR.

Main food sources of Vitamin K


High Content Cabbage, Brussels sprouts, spinach, kale, turnips
Average Content Asparagus, avocado, broccoli, carrots, celery, cauliflower, red cabbage, cucumber, watercress, green beans, oils (canola, olive, soya), lettuce (Boston, Iceberg, romaine), fresh parsley, leek, green peas, tomato

So, in answer to the original question, no, it isn’t necessary to avoid green vegetables because the Vitamin K they contain enables a better control of both coagulation and medication. Good to know, those who have the most difficulty managing their INR are often those who do not eat (or do not eat enough) Vitamin K and green vegetables.

Our heart-healthy menus are approved by the nutritionists at EPIC, Montreal Heart Institute’s Center for Preventative Medicine, even for their anticoagulation therapy patients. Why not give them a try to help plan your meals?



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Jef L'Ecuyer

Jef L’Ecuyer

Registered Dietitian, RD at

Member of the Quebec College of Dietitians (OPDQ) and Dietitians of Canada,Jef graduated from McGill University in December 2014. Recently graduated and passionate about culinary arts, Jef poses a simple, effective and practical look at daily meal planning. With this in mind, she works in conjunction with the mission of SOSCuisine…

Jef L'Ecuyer

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7 Responses to “Blood Thinners and Greens: A Mix to Avoid?”

February 11, 2019 at 4:25 pm, Virginia Davis said:

Your article did not mention collard greens. Are they high in vitamin K as well? My mother loves collard greens and taking Warfarin at the moment. Her doctor has said no to green veggies. I hope that this article can apply to her.

Cinzia Cuneo

February 11, 2019 at 4:33 pm, Cinzia Cuneo said:

Hi Virginia,
Yes, the same applies to collard greens. Your mother needs to keep her consumption always at about the same level.

February 19, 2019 at 12:52 pm, marlin said:

ALWAYS first check with your healthcare pro before starting supplements OR changing your dietary preferences. You can shock your metabolism and totally mess it up. What works for some don’t work for all. Many supplement also interact with med’s or other supplements. Don’t take chances, as first.

February 20, 2019 at 6:21 am, Spencer Ryce said:

Blood thinners are medicines that prevent blood clots from forming. They also keep existing blood clots from getting larger. Clots in your arteries, veins, and heart can cause heart attacks, strokes, and blockages.

There are two main types of blood thinners. Anticoagulants such as heparin or warfarin (also called Coumadin) slow down your body’s process of making clots. Antiplatelet drugs, such as aspirin, prevent blood cells called platelets from clumping together to form a clot.

March 15, 2019 at 1:16 pm, Luciano Tortorici said:

Very clarifying and helpful article. Thank you.

April 12, 2019 at 12:05 pm, Daniel said:

Hello, I have been taking warfarin and clopidogrel for several years now, 10mg warfarin daily and 75mg of clopidogrel. I also take nicorandil,bisiprolol,atorvastatin,ramipril and bumetanide. My INR has dropped to 1.2 and I’m not able to travel to the hospital for two or three days due to mobility issues, I have no money to pay for public transport either. My diet has changed for the better recently and I’m consuming many more potions of green leafy vegetables. Could this have had such a drastic impact on my INR? should I be worried?

Jef L'Ecuyer

April 12, 2019 at 12:14 pm, Jef L'Ecuyer said:

> Hello Daniel!

Improving your diet and consuming more leafy greens can definitely have an effect on your INR. You should check-in with your medical team to make sure your medication is adjusted accordingly.

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