If you are taking blood thinners or anticoagulants for a medical condition, you may need to monitor your intake of vitamin K-rich foods. Vitamin K plays an essential role in the chemical process of forming blood clots in your body. What you eat and drink has the potential to affect how your medication works. Too much vitamin K could interfere with the drugs you are taking and make them ineffective, causing dangerous unintended consequences to your health.
What Is Vitamin K?
Whenever you are injured, whether it is a paper cut or a serious laceration, your body calls upon vitamin K to help protect you from uncontrolled bleeding. Vitamin K is responsible for blood coagulation and is crucial for the formation of blood clots, which are required for the repair of damaged vessels.
Vitamin K actually comprises of two fat-soluble components: vitamin K1— phylloquinone, and vitamin K2 — menaquinone. Vitamin K1 is the main dietary form found primarily in green leafy vegetables. Vitamin K2 is present in animal-based and fermented foods and also produced by bacteria in your colon.
Vitamin K Interactions
Vitamin K combined with anticoagulant medications has the potential to cause a serious and dangerous outcome. Warfarin (Coumadin) is the most well-known blood thinner, but other forms of this type of medication include phenprocoumon, acenocoumarol and tioclomarol. These drugs are prescribed if you are at risk of easily and too quickly forming blood clots, which could become dislodged and obstruct the flow of blood to your heart, lungs or brain.
Warfarin works against vitamin K by decreasing its activity. Since vitamin K is essential for clot-making factors in your liver, it's important to keep your vitamin K intake as consistent as possible in order for warfarin to work properly. Suddenly eating foods high in vitamin K may decrease the effect of warfarin.
The Warfarin Diet
When taking warfarin, the food you eat can have an affect on how effective the drug is in controlling coagulation. To balance your risk of excessive bleeding against the risk of clotting, your doctor will need to monitor how long it takes your blood to form a clot using laboratory measurements called the International Normalised Ratio or INR, and Prothrombin Time, or PT.
When the INR reading is too high, it means that your blood is too thin, and you are at a higher risk for bleeding. If the INR is too low, your blood is too thick and you may be at a higher risk for developing a blood clot.
In other words, eating too much vitamin K rich foods can decrease your INR. This means you will lower the level of warfarin in your body and be more likely to form a blood clot. Conversely, if you consume less vitamin K rich foods, it can increase your INR and help protect you from blood clotting.
Read more: 5 Important Food Tips for Patients Taking Coumadin
Consistency Is the Key
When taking warfarin, you do not need to avoid foods that contain vitamin K, but you do need to be consistent in the amount of your intake. The important part of a warfarin diet is that you don't make big changes to how much or what you eat in your diet.
For example, if you don't normally eat spinach every day, which is high in vitamin K, don't suddenly indulge by consuming a huge spinach salad. Having a cheat day could result in a harmful consequence.
For this reason, it's important to know the vitamin K content in all the foods you enjoy and know how much you can eat to stay healthy and keep your INR in check.
How Much Can You Eat?
You should not avoid foods containing vitamin K because they are part of a healthy balanced nutrient-rich diet. Your goal should be to eat a relatively similar amount of vitamin K each week. Be mindful of portions and discuss your regular diet with your doctor in case your warfarin dosage needs to be adjusted.
For optimal health, the Dietary Guidelines for Americans recommends a daily intake of 90 micrograms of vitamin K for adult women and 120 milligrams for adult men. Keeping your daily value (DV) within this range on a consistent basis will help keep your PT/INR levels stable.
Vegetables Low in Vitamin K
To help manage your diet, choose from a variety of vegetables low in vitamin K. Food containing the lowest amounts of vitamin K — less than 14 percent DV, per 1-cup serving, include:
- Turnips (raw or cooked) — 0.1 micrograms
- Beets (raw or cooked) — 0.3 micrograms
- Sweet Corn (raw or cooked) — 0.5 micrograms
- Onion (raw or cooked) — 1 microgram per 1 medium onion
- Rutabagas (raw or cooked) — 0.5 micrograms
- Pumpkin (cooked) — 2 micrograms
- Winter squash(cooked) — 2 micrograms
- Summer squash (cooked) — 3 micrograms
- Eggplants (cooked) — 3 micrograms
- Bamboo shoots (raw or canned) — 0 micrograms
- Mushrooms (raw or cooked) — 0 micrograms
- Tomatoes (cooked) — 7 micrograms
- Tomatoes (raw) — 14 micrograms
- Cucumbers (raw) — 17 micrograms
- Iceberg lettuce (raw) — 17.4 micrograms
Fruits Low in Vitamin K
- Watermelon — 0.2 micrograms
- Litchis — 0.8 micrograms
- Bananas — 0.6 micrograms
- Pineapple — 1.2 micrograms
- Apples — 4 micrograms per fruit
- Nectarines — 3 micrograms per fruit
- Strawberries — 3 micrograms
- Peaches — 4 micrograms per fruit
Limit or avoid citrus fruits and use caution when eating blueberries, mangoes and pomegranate, which can affect PT/INR.
Grains Low in Vitamin K
All grain products contain very little or no vitamin K. White rice, plain pasta, whole-wheat bread and quinoa can be good choices because they do not provide any vitamin K to your diet. Some examples of starches low in vitamin K — 1 percent DV or less — per 1-cup serving, are:
- Brown rice — 0.4 micrograms
- Couscous — 0.2 micrograms
- Cornmeal — 0.4 milligrams
- Bulgar — 0.9 milligrams
- Pearl Barley — 1.3 micrograms
- Millet — 0.5 micrograms
Meat and Other Foods
Meat generally is low in vitamin K, except canned fish packed in oil and abalone. Dairy products, including eggs, are also low in vitamin K. Most beans and legumes, with the exception of black-eyed peas, soy and green beans are low in vitamin K.
Read more: Vitamin K Toxicity Symptoms
Foods to Limit or Avoid
Some foods, especially green leafy vegetables, contain a very high content —over 200 to 450 percent DV — of vitamin K per half-cup serving. You should limit these foods to one serving a day and not combine them with other foods containing vitamin K on your Coumadin diet. Some of these foods include:
- Boiled kale —442 percent DV
- Boiled spinach — 370 percent DV
- Boiled collard greens —332 percent DV
- Boiled Swiss chard — 239 percent DV
Some other foods that you should limit to no more than three servings per day contain 40 to 100 percent of your DV per cup:
- Raw endive — 96 percent DV
- Boiled Brussels sprouts — 91 percent DV
- Raw broccoli — 77 percent DV
- Romaine lettuce — 40 percent DV
If you eat more foods rich in vitamin K, or change your diet in any way, you should check your blood more frequently and work with your doctor to find the right dose of warfarin for you.
- National Institutes of Health: "Vitamin K"
- National Institutes for Health Clinical Center: "Important Drug and Food Information"
- University of Iowa: "Blood Tests That Are Needed When Taking Warfarin"
- American Heart Association: "A Patient's Guide to Taking Warfarin"
- Dietary Guidelines: "Daily Nutritional Goals for Age-Sex Groups Based on Dietary Reference Intakes and Dietary Guidelines Recommendations"
- MyFoodData: "Foods Low in Vitamin K for a Warfarin (Coumadin) Diet"