Should you avoid foods rich in vitamin K on a blood thinner?

When I work with patients who have been prescribed a blood thinner, such as warfarin, one question I often hear is whether they need to avoid green fruits and vegetables that are rich in vitamin K.

The answer is usually no. While vitamin K can make certain blood thinners less effective, that doesn’t mean you need to cut out leafy greens or other vitamin K-rich foods altogether. Instead, the goal is to keep your intake steady from week to week.

To understand why consistency matters, it helps to know how blood thinners work. If you’re at risk for a heart attack or stroke, your doctor may prescribe a blood thinner, such as warfarin, to help prevent harmful blood clots from forming or getting larger.

Because these medications affect how your blood clots, some types — especially warfarin — require extra attention to your diet.

Important things to know about vitamin K

Vitamin K is a fat-soluble nutrient that your body needs for healthy bones and to help your blood clot normally. This nutrient is found in many green fruits and vegetables, especially leafy greens.

For a blood thinner to work well, it’s important to keep your vitamin K intake as consistent as possible. A large increase in vitamin K can make your blood more likely to clot, while a large decrease can make your blood less likely to clot.

You don’t need to avoid vitamin K or follow a low-vitamin K diet when taking a blood thinner. The key is to keep the amount of vitamin K you eat about the same from week to week, so your medication can work as expected and your blood clotting levels stay stable.

For example, if you usually eat a half-cup of vegetables rich in vitamin K each day, you can keep eating that amount. The key is to stay consistent and avoid major changes from week to week.

Leafy greens and vegetables that are high in vitamin K include:

• kale
• spinach
• collard or mustard greens
• Swiss chard
• turnip greens
• Brussels sprouts
• broccoli
• cabbage

A note about vitamin K in supplements

If you don’t get the recommended daily amount of vitamin K in your diet, your healthcare team may recommend a vitamin supplement.

For most adults, the recommended daily amount of vitamin K is about 90 to 120 micrograms per day. Your needs may be different, especially if you take warfarin or another blood thinner, so talk with your healthcare team before making major changes to your diet or supplements.

It’s important not to take more than one supplement that contains vitamin K unless your doctor recommends it. For example, one multivitamin that contains 100% of your daily vitamin K can help keep your intake consistent.

The bottom line about vitamin K

The most important step is to take your blood thinner medication exactly as prescribed and get regular blood clotting tests, if your doctor recommends them. If keeping your vitamin K intake consistent feels difficult, ask your healthcare team whether working with a dietitian could help. A dietitian can review the vitamin K in your usual meals and help you make a plan that works for you.