Warfarin is a commonly prescribed anticoagulant (blood thinner) that helps prevent blood clots from forming or growing larger. It’s sold under the brand names Coumadin, Jantoven, and Marevan. While warfarin is highly effective, it does require careful management due to its narrow therapeutic range and potential for food and drug interactions.
Introduction
Certain fruits contain high amounts of vitamin K, which plays an important role in blood clotting. Eating too much vitamin K can counteract the effects of warfarin by stimulating the production of clotting factors. For this reason, it’s important for people taking warfarin to monitor and limit intake of vitamin K-rich fruits and vegetables to maintain consistent anticoagulation.
Fruits High in Vitamin K to Avoid
The fruits highest in vitamin K that should generally be avoided or limited when taking warfarin include:
- Kiwifruit
- Prunes
- Raisins
- Blueberries
- Blackberries
- Figs
- Avocados
Kiwifruit is exceptionally high in vitamin K, containing approximately 85 micrograms per 100 grams. Just one kiwifruit provides over 100% of the recommended daily intake for adults. Prunes, raisins, blueberries, blackberries, and figs contain 15-70 micrograms per 100 grams. While avocados are lower in vitamin K than many fruits, containing around 30 micrograms per 100 grams, they are often consumed in larger quantities. Even a half of an avocado can provide 50% or more of the daily recommended vitamin K intake.
Fruits Lower in Vitamin K
The fruits lower in vitamin K that are generally considered safe to eat in moderation when taking warfarin include:
- Apples
- Grapes
- Oranges
- Pears
- Pineapples
- Mangos
- Strawberries
- Raspberries
- Plums
- Peaches
- Cherries
- Papaya
- Kumquats
- Cranberries
These fruits contain no more than 10 micrograms of vitamin K per 100 grams. While they can be consumed in moderation, portion sizes should still be limited and intake should be consistent from day to day.
Managing Fruit Intake on Warfarin
Get Regular INR Monitoring
The best way to manage warfarin therapy is to have frequent International Normalized Ratio (INR) monitoring. This blood test measures how long it takes your blood to clot. Your doctor will determine your target INR range based on your medical condition. More frequent monitoring, such as weekly or biweekly, is recommended when first starting warfarin or if doses are being adjusted.
Limit Serving Sizes
Even fruits low in vitamin K should be eaten in limited serving sizes. Most experts recommend limiting fruit intake to one or two servings per day. One serving is typically defined as:
- 1 medium apple, orange, pear, etc.
- 1⁄2 cup chopped, cooked, or canned fruit
- 1⁄4 cup dried fruit
- 1⁄2 cup fruit juice
Maintain a Consistent Diet
Try to keep your daily vitamin K intake relatively constant by maintaining a consistent diet. Dramatically increasing or decreasing your vitamin K intake can make your INR fluctuate outside your target range. Avoid binge eating fruits high in vitamin K and keep fruit intake steady from day to day.
Watch for New Food Interactions
If you try a new fruit, pay close attention to any changes in your INR. Certain individuals could be more sensitive to vitamin K interactions with warfarin. You may need to avoid fruits that most people can tolerate in moderation.
Talk to Your Pharmacist
Consult your pharmacist about all medications, supplements, and vitamins you take to identify any potential drug or nutrient interactions with warfarin. Your pharmacist can also provide a comprehensive list of foods to avoid.
Vitamin K Content of Common Fruits
| Fruit | Serving Size | Vitamin K (mcg) |
|---|---|---|
| Kiwifruit | 1 medium (69g) | 87.9 |
| Prunes | 1⁄4 cup (40g) | 59.5 |
| Blueberries | 1⁄2 cup (74g) | 19.5 |
| Blackberries | 1⁄2 cup (74g) | 19.8 |
| Avocado | 1⁄2 medium (68g) | 13.5 |
| Raisins | 1⁄4 cup (38g) | 12.6 |
| Figs | 1 medium (50g) | 11 |
| Grapes | 1 cup (151g) | 8.7 |
| Oranges | 1 medium (131g) | 6.6 |
| Peaches | 1 medium (150g) | 6.3 |
| Plums | 1 medium (66g) | 5.7 |
| Strawberries | 1 cup, whole (144g) | 4.5 |
| Cherries | 1 cup (155g) | 4.3 |
| Apples | 1 medium (182g) | 2.7 |
| Pineapple | 1 cup chunks (165g) | 2.6 |
| Mangos | 1⁄2 medium (165g) | 1.6 |
| Papaya | 1 cup cubes (140g) | 1.5 |
| Raspberries | 1 cup (123g) | 1.2 |
| Pears | 1 medium (178g) | 1.1 |
Tips for Eating Fruit on Warfarin
Here are some tips for safely consuming fruit while taking warfarin:
- Enjoy fruits lower in vitamin K like apples, grapes, and berries
- Limit portion sizes to 1⁄2 – 1 cup or 1 medium fruit serving
- Avoid fruits high in vitamin K like kiwis, avocados, and prunes
- Monitor INR regularly and watch for new interactions
- Consume a consistent amount of fruit and vitamin K every day
- Talk to your doctor or pharmacist about your diet
- Read nutrition labels and choose low-vitamin K juices or frozen fruits
- Substitute higher vitamin K fruits with lower vitamin K options
- Spread fruit intake throughout the day rather than consuming all at once
- Rinse produce thoroughly to remove any surface pesticide residues
Potential Impact of Fruit on INR Levels
Eating fruits high in vitamin K can potentially cause your INR levels to drop below your target range. This could place you at increased risk of developing dangerous blood clots. The impact fruit can have on your INR depends on a number of factors:
- Your individual warfarin dosing – People have varying sensitivities to vitamin K intake based on their regular dose of warfarin and ability to metabolize it.
- Amount of fruit eaten – Larger quantities of even lower vitamin K fruits can potentially affect INR levels.
- Consistency – Sudden spikes or drops in fruit and vitamin K intake tend to affect INR more than stable intake.
- Other vitamin K intake – High intake of greens like kale or spinach in addition to fruit can compound interactions.
- Frequency of INR monitoring – Frequent monitoring helps quickly identify any interactions before major dosage changes become necessary.
- Other medical conditions and medications – Factors like liver or kidney disease, antibiotics, or supplements can all influence warfarin metabolism and fruit interactions.
The best approach is to start with low vitamin K fruits, limit serving sizes, and pay close attention to any fluctuations in INR after trying new fruits. Consult your doctor promptly if you experience unexplained changes in INR.
Conclusion
In summary, people taking warfarin need to monitor and limit intake of vitamin K-rich fruits like kiwis, avocados, and prunes, as they can interfere with warfarin’s effects. Focus on fruits lower in vitamin K and consume limited portion sizes of one or two servings per day maximum. Keep fruit intake steady from day to day and have your INR monitored frequently. With some careful dietary management, you can still enjoy the nutritional benefits of fruit while safely taking warfarin.