Blood Thinners and Greens: A Mix to Avoid?
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:
- Moving home
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)
- Devil’s Claw
- Dong Quai
- Garlic capsules
- Ginko biloba
- Vitamin E (in doses larger than 400 units/day)
- Those which reduce INR values:
- Coenzyme Q10
- 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
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?
- Nutescu, E. A., Shapiro, N. L., Ibrahim, S., & West, P. (2006). Warfarin and its interactions with foods, herbs and other dietary supplements. Expert opinion on drug safety, 5(3), 433-451.
- OPDQ. (2013). Manuel de nutrition clinique – Traitement anticoagulant et vitamine K. Retrieved from: http://opdq.org/mnc/regime-controle-en-vitamine-k/
- Ordre des Pharmaciens du Québec. (2005). Anticoagulothérapie en milieu ambulatoire. Retrieved from: http://www.opq.org/doc/media/809_38_fr-ca_0_ld_anticoagulotherapie_pharm.pdf
- PENnutrition. (6 octobre 2008). Drug/Nutrient Interactions – Key Practice Points. Retrieved from: http://www.pennutrition.com/KnowledgePathway.aspx?kpid=11728&pqcatid=146&pqid=11785
- Schurgers, L. J., Shearer, M. J., Hamulyák, K., Stöcklin, E., & Vermeer, C. (2004). Effect of vitamin K intake on the stability of oral anticoagulant treatment: dose-response relationships in healthy subjects. Blood, 104(9), 2682-2689.
- Uniprix. (2016). Lexique des médicaments – Coumadin (warfarine). Retrieved from: https://www.uniprix.com/fr/lexique-medicaments/741/coumadin
- UpToDate. (13 avril 2016). Overview of Vitamin K. Retrieved from http://www.uptodate.com/contents/overview-of-vitamin-k
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