Warfarin Diet: Foods To Eat And Avoid

If you’ve been prescribed warfarin, you’ve likely been cautioned about how your diet can interact with it. 

A warfarin diet can help you stay safe and reduce the risk of complications, some of which can be serious.

So what foods should you eat, and which are best to avoid while taking warfarin? Keep reading to find out.

What is warfarin (Coumadin)?

Warfarin is the drug name of a commonly-used anticoagulant with the brand names Coumadin and Jantoven. Many people still refer to warfarin as Coumadin, even if it is a generic, non-brand name version.

The FDA approved warfarin in 1954, and until recent years warfarin was the only medication approved to help reduce the risk of stroke and heart attack in patients with atrial fibrillation.

The dosage for warfarin usually starts between two and five milligrams once daily. Your healthcare provider might increase the dose as needed to achieve a therapeutic dose (the amount that keeps your blood at the target thickness). Still, the dosage usually doesn’t exceed 10 milligrams daily.

Warfarin acts by blocking vitamin K from making clotting factors which help form clots and thicken the blood. Vitamin K is a nutrient found in some foods and supplements.

Warfarin is most typically prescribed to treat atrial fibrillation, a type of irregular heartbeat that can increase your risk of developing blood clots. Blood clots can travel to your heart, brain, or other vessels and block blood flow, which can be fatal.

What are the side effects of Warfarin?

The most common side effects of warfarin include increased bleeding and bruising. You might experience more nosebleeds or have more bleeding from minor cuts and scrapes than you did before you started taking warfarin.

Other potential side effects of taking warfarin include:

  • Gas
  • Abdominal pain
  • Bloating
  • Change in the way things taste
  • Loss of hair
  • Feeling cold or having chills

While it’s rare, warfarin does have a black box warning regarding its potential to cause severe bleeding. If you have any of the following symptoms, seek emergency medical care right away. 

Signs of internal or otherwise serious bleeding include the following:

  • Bloody, red, or tarry bowel movements (a sign of a bowel bleed)
  • Spitting or coughing up blood
  • Heavy bleeding with your menstrual period
  • Pink, red, or dark brown urine
  • Coughing up or vomiting material that looks like coffee grounds
  • Small, flat, round red spots under the skin
  • Unusual bruising or bleeding
  • Continued oozing or bleeding from minor cuts

vitamins for energy

Diet and warfarin: what’s the link?

The main nutrient that interacts with warfarin is vitamin K. Vitamin K helps blood to clot, and warfarin does the opposite by trying to slow coagulation. 

While many people taking warfarin are under the impression that they need to avoid vitamin K-rich foods altogether, this isn’t necessarily the case. Vitamin K is in many nutrient-rich foods like dark green vegetables, which can benefit your health.

The most important aspect to consider with vitamin K foods is your consistency in eating them. 

If you rarely eat vitamin K foods, then you should avoid making abrupt changes and suddenly increasing the amount of vitamin K you consume.

Likewise, if you normally eat a consistent amount of vitamin K, drastically decreasing this amount can change the thickness of your blood and alter the way warfarin works.

For instance, if you eat a lot of vitamin K-rich foods when you normally don’t, it might make your blood thicker by promoting clotting and potentially increase your risk of developing a blood clot.

On the other hand, if you normally eat vitamin K-rich foods regularly and then stop suddenly while taking warfarin, your blood might become too thin. Blood that is too thin and is slow to clot increases your risk of severe bleeding.

How can I know how my diet is impacting my warfarin dose?

Your healthcare provider will regularly monitor your blood thickness to ensure you take the correct dose. The blood tests commonly monitored while you’re on warfarin include prothrombin time and your INR. 

The prothrombin time measures how long it takes your blood to clot. The INR (international normalized ratio) determines if your blood thickness is in the therapeutic range.

If you’ve made drastic changes to your diet in terms of vitamin K intake, it will likely show up in these tests.

An INR of 1.1 or less is normal in healthy people. If you need to take warfarin for Afib or blood clots, an INR of 2-3 is considered normal. 

If your INR is high, it means your blood is clotting more slowly, and if it’s low, it means it’s clotting more quickly. A high INR can lead to severe bleeding problems, while a low INR might lead to blood clots.

For instance, if your INR is below 2, your healthcare provider might increase your warfarin dose to help it clot more slowly and reach a more therapeutic INR of 2-3.

If you plan to change your consumption of vitamin K, be sure to speak with your healthcare provider. They may suggest changing your warfarin dose to compensate to avoid increased bleeding or blood clot risk.

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Foods to avoid while taking warfarin

Remember that you don’t need to avoid vitamin K altogether, but do aim to keep your intake consistent. You should avoid excessive vitamin K intake, as this might promote more blood clotting and lead to a potentially fatal blood clot.

Foods rich in vitamin K (keep consistent – don’t overdo)

The highest vitamin-K foods are green leafy vegetables, as well as other green vegetables and herbs.

Highest vitamin K content:

  • Kale
  • Spinach
  • Collards
  • Turnip greens
  • Beet greens
  • Dandelion greens
  • Mustard greens

Other moderate vitamin K foods:

  • Brussel sprouts     
  • Broccoli   
  • Onions 
  • Lettuce 
  • Cabbage     
  • Asparagus    
  • Endive    
  • Parsley   
  • Okra    

Other higher-vitamin K foods

  • Kiwi fruit (moderate source)

Foods to eat while taking warfarin

Always speak with your healthcare provider regarding your diet while taking warfarin, especially when it comes to making changes in your diet.

The good news is that aside from vitamin K foods, you don’t have to worry much about other foods interacting with warfarin.

A balanced, healthy diet including protein, whole grains, and healthy fats is ideal when taking warfarin to support heart health. (Remember that heart conditions are the most common reason warfarin is prescribed). 

Quality protein

Choose lean protein sources when you can to promote heart health. Some good choices include:

  • Poultry (skinless)
  • Lean beef
  • Fish
  • Eggs
  • Beans & lentils
  • Soybeans (tofu, edamame, etc.)*

*Some soy products are higher in vitamin K, such as natto (fermented soybeans). You can likely safely eat other soy products in moderation on warfarin.

Healthy fats

Foods that are rich in unsaturated fatty acids can promote healthy cholesterol levels and heart health. 

  • Avocados (a source of vitamin K, so eat in moderation)
  • Plant oils (olive, canola, flaxseed, avocado oil, etc.)
  • Nuts
  • Seeds (especially flax and chia seeds)
  • Oily fish like salmon, mackerel, sardines, etc.*

*Very high intakes of omega-3 fatty acids, such as from fish oil and omega-3 supplements, can act as a blood thinner. Eating omega-3-rich foods has a lower risk of thinning your blood compared to high-dose omega-3 supplements

Whole grains

Whole grains are rich in fiber and nutrients that can support your heart and overall health.

  • Whole wheat bread, pasta, tortillas, crackers, etc. (no enriched flour)
  • Oats
  • Brown rice
  • Barley
  • Bulgur 
  • Millet
  • Popcorn

Low vitamin-K vegetables

There are plenty of vegetables that are lower in vitamin K that you can safely enjoy while taking warfarin.

  • Artichoke
  • Black beans
  • Carrots
  • Cauliflower
  • Celery
  • Corn
  • Cucumber
  • Garbanzo beans
  • Green beans
  • Green pepper
  • White mushrooms
  • Onions
  • Parsnips
  • Peas (½ cup)
  • Potatoes
  • Pumpkin
  • Radish
  • Red cabbage
  • Summer squash
  • Sweet potato
  • Tomato
  • Turnips

Fruit

Some fruits contain some vitamin K (those marked with a *), but are likely safe to eat in moderation or small amounts. Fruit isn’t nearly as high in vitamin K as dark leafy green vegetables.

Some low- and medium*-vitamin K fruits include:

  • Pears
  • Apples
  • Bananas
  • Strawberries
  • Citrus fruits
  • Grapes*
  • Blueberries*
  • Blackberries*
  • Pomegranates* and pomegranate juice*

Other things to avoid while taking warfarin 

Alcohol

Alcohol can act as a natural blood thinner by preventing blood cells from sticking together. Drinking large amounts of alcohol might increase your risk of severe bleeding while taking warfarin, so aim to keep your alcohol intake low- to moderate if you choose to drink.

Pregnancy/breastfeeding

Blood thinners like warfarin shouldn’t be taken during pregnancy. Taking these types of blood thinners can increase the risk of hemorrhaging (losing a large amount of blood due to a broken blood vessel) and problems for the mother and baby.

Blood thinners are only prescribed during pregnancy if the potential benefits outweigh the risks. If you’re taking a blood thinner and are planning to become pregnant, you should notify your healthcare provider immediately.

Certain juices 

Grapefruit juice

Grapefruit juice interacts with many medications and can impact the way they work. Compounds in grapefruit juice can increase the level of warfarin in your blood, which could cause increased bleeding. Avoid drinking grapefruit juice while taking warfarin.

Contrary to some popular belief, there aren’t enough well-designed studies on large populations proving a negative interaction between cranberry juice and warfarin. Therefore, drinking cranberry juice in moderation is likely safe while taking warfarin.

Certain supplements

Some supplements contain vitamin K. You should speak to your healthcare provider or pharmacist if you’re taking any herbal or dietary supplements such as:

  • Alfalfa
  • Angelica
  • Aniseed
  • Arnica
  • Asafoetida
  • Chamomile
  • Echinacea
  • Fenugreek
  • Feverfew
  • Garlic
  • Ginger
  • Ginkgo biloba
  • Ginseng
  • Horse chestnut
  • Melilot
  • Prickly ash
  • Quassia
  • Red clover
  • Saint John’s wort
  • Saw palmetto
  • Spirulina
  • Sweet woodruff
  • Tonka beans

Omega-3 supplements

Omega-3 supplements, including fish oil, can act as an anticoagulant. These should also be addressed with your healthcare team while taking warfarin.

Multivitamins containing vitamin K should also be discussed while taking warfarin.

Green juice drinks

Drinks made from dark leafy green vegetables (green juices or green drinks) might contain significant vitamin K levels. Avoid these types of drinks since they could interfere with your warfarin. 

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Should you take warfarin with food?

Warfarin doesn’t commonly cause stomach upset, so it can be taken with or without food. If you experience nausea or stomach upset when taking warfarin, take it with food or a glass of milk to reduce these unpleasant symptoms.

What time to take warfarin

You can take warfarin at any time of the day, but it’s often recommended to take it in the evening. Try to take warfarin at the same time of day consistently – whatever time is most convenient for you to remember is the best.

The reason it’s recommended to take it in the evening is that the evening meal is usually the one with the most variable vitamin K content.

Staying safe while taking a blood thinner

Be cautious when using sharp objects

If you’re using knives, razors, or other sharp objects, be extremely careful and wear protective clothing when you can. Accidentally cutting yourself can lead to more severe blood loss than if you weren’t taking a blood thinner, so try to offload jobs that require using sharp objects (cutting wood with an axe, for instance) to others when you can.

Take medication as prescribed, and keep up with routine lab monitoring

Accidentally taking too much or too little warfarin can be problematic. Take warfarin as prescribed to minimize your risk of serious issues like increased bleeding or blood clots.

Keep up with routine blood work that is required while taking warfarin. This helps your healthcare provider adjust your warfarin to make sure you’re taking the right amount. If you skip these lab tests, you might be at higher risk of complications from taking too much or too little warfarin.

Conclusion

Foods rich in vitamin K promote blood clotting, while warfarin works to slow blood clotting. 

Drastic changes in your vitamin K intake can alter the effectiveness of warfarin.

Aim to eat vitamin K-rich foods in moderation. To be safe, avoid eating large portions of very high vitamin K foods like spinach, kale, and other dark leafy greens.

Eat a heart-healthy diet while taking warfarin, which includes quality lean protein, whole grains, healthy fats, and a variety of low- to moderate-vitamin K fruits and vegetables.

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Sources

  1. Zikria J, Goldman R, Ansell J. Cranberry juice and warfarin: when bad publicity trumps science. Am J Med. 2010 May.
  2. Heran BS, Allan GM, Green L, Korownyk C, Kolber M, Olivier N, Flesher M, Garrison S. Effect of medication timing on anticoagulation stability in users of warfarin (the INRange RCT): study protocol for a randomized controlled trial. Trials. 2016 Aug.

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