Consistency is key — especially when the food you eat can affect your medications. It’s important to be aware of potential dietary interactions when it comes to safely taking medications. Several foods can interact with certain medications, causing them to either work too much or not enough.
Warfarin (Coumadin, Jantoven) is an anticoagulant medication (blood thinner) used to treat and prevent serious blood clots in people at risk for developing them. Blood clots can be dangerous and lead to heart attacks, strokes, or even death. Warfarin doses vary for every person, and they can be tricky to balance because — among other things — it largely depends on your diet.
In this article, we’ll discuss common foods that interact with warfarin and tips on how to handle those interactions safely.
Why is vitamin K harmful for people taking warfarin?
Vitamin K is a nutrient that your body uses to help form blood clots. This vitamin is important because it prevents excessive bleeding. The most common source of vitamin K comes from your diet.
The relationship between warfarin and vitamin K is an interesting one. Warfarin is a blood thinner that works by stopping vitamin K from making proteins used for blood clotting. Too much warfarin can lead to excess bleeding, and too much vitamin K can cause your blood to clot faster.
So while warfarin causes your blood to clot less, vitamin K causes your blood to clot more. And if you’re not consistent with the amount of vitamin K in your diet, it can cause problems. Consuming an inconsistent dietary amount of vitamin K makes it harder for warfarin to do its job and can affect the required blood tests you go for while taking warfarin.
International normalized ratio (INR) is a blood test that measures if your blood clots normally. People taking warfarin have their INR levels regularly checked to determine how well the medication is working.
Your healthcare provider uses your INR level to adjust your warfarin dose. A higher INR means more bleeding (fewer clots), and your warfarin dose may need to be lowered. A lower INR means less bleeding (more clots), and your warfarin dose may need to be raised.
It can be challenging to find the right dose because both vitamin K and warfarin can affect your INR in opposite ways. Warfarin raises your INR while vitamin K lowers your INR. A balance between the two is necessary.
What foods can interact with warfarin?
There are many foods and drinks that contain vitamin K. This section doesn’t include every dietary item that could possibly affect your INR level — just some notable ones. Be sure to discuss your regular diet with your healthcare provider when taking warfarin.
Dark, leafy green vegetables
Some of the most commonly consumed foods that are rich in vitamin K are dark, leafy green vegetables. Some examples of those include:
Kale
Endive
Spinach
Mustard greens
Turnip greens
Collard greens
Swiss chard
Brussel sprouts
Broccoli
If you’re worried you have to cut out these vegetables completely, don’t fret. Instead of avoiding eating leafy green vegetables, warfarin works best when the level of vitamin K in your body stays the same. So if you typically eat leafy greens, you can continue to eat your usual serving.
However, if you decide to change the amount of leafy greens you’re eating — either eating more or eating less — you need to let your provider know before making these changes. These adjustments in your diet can raise your risk of serious blood clots or dangerous bleeding while you’re taking warfarin.
Beverages:
Two beverages are often mentioned by healthcare providers when it comes to potential warfarin interactions — cranberry juice and green tea. However, the evidence is conflicting on how severe the interaction is between warfarin and these drinks. It’s always best to discuss this with your healthcare provider before adding or eliminating them from your routine diet.
Cranberry juice:
Although cranberry juice contains little vitamin K, whether or not it interacts with warfarin is controversial. Some reports say taking cranberry juice and warfarin together can cause higher INR levels, which means a higher risk of bleeding.
On the other hand, studies have also shown that there is no interaction between the two. However, most experts agree drinking cranberry juice in moderation (about 8 fluid ounces per day or less) while taking warfarin shouldn’t affect your blood’s ability to clot.
Green tea:
In a case report, a person who drank large amounts (a half-gallon or more per day) of green tea while taking warfarin experienced low INR levels. This interaction has not been investigated further since this case report, so we don’t know if green tea would have this effect for everyone taking warfarin. However, moderate amounts of green tea contain little vitamin K and are not likely to affect warfarin.
Alcohol:
Alcohol use can change the way warfarin works. Heavy drinking can change the level of warfarin in your body. Heavy drinking is defined as more than 7 drinks per week for people assigned female at birth and more than 14 drinks per week for people assigned male at birth.
Studies have found that episodic heavy drinking — occasionally drinking five or more drinks at a time — can raise the levels of warfarin and the risk of major bleeding, such as stomach or intestinal bleeding. On the other hand, excessive daily alcohol use has the opposite effect — it can lower the amount of warfarin in your body and raise your risk of clotting.
If you are going to drink, do so in moderation. The American Heart Association (AHA) recommends that people taking warfarin limit their alcohol consumption to no more than 1 to 2 drinks per day for people assigned male at birth or 1 drink per day for people assigned female at birth. But before drinking any alcohol with warfarin, it’s best to talk to your healthcare provider.
What vegetables can I eat while taking warfarin?
There are many vegetables that you can eat without worrying about whether you are eating it consistently or not. These vegetables are low in vitamin K and unlikely to affect your INR levels.
Some of these vegetables include:
Artichokes
Carrots
Cauliflower
Celery
Corn
Green beans
Onions
Potatoes
Radishes
Red cabbage
Tomatoes
What can happen if I eat too much of the foods that interact with warfarin?
As discussed, foods high in vitamin K can affect how warfarin works. Eating too much of these foods at one time or eating inconsistent amounts can cause warfarin not to work as well and lead to the development of a dangerous blood clot.
seek emergency medical care if you are experiencing any of the following signs and symptoms of a blood clot:
Pain, swelling, and redness in your legs
Difficulty breathing
Chest pain
Trouble moving your limbs
Trouble seeing, walking, or speaking
Severe headache
The bottom line
Although there are many foods that interact with warfarin, you don’t necessarily need to stop eating them. Eating consistent amounts or drinking small-to-moderate amounts of these dietary items shouldn’t affect warfarin therapy too much. However, if you decide to change your diet or drinking habits, you should contact your healthcare provider first so that they can make any dose changes.
