Vitamin K Supplements and Warfarin: How to Keep INR Stable

If you're on warfarin, you know how frustrating it can be when your INR jumps around like a ping-pong ball. One week it's perfect, the next it's dangerously high or too low - and you're stuck wondering why. You're not alone. About half of people taking warfarin experience these wild swings, and each one puts you at risk for a clot or a bleed. But what if the problem isn't your warfarin dose - it's your vitamin K?

Why Your INR Keeps Fluctuating

Warfarin works by blocking vitamin K from helping your blood clot. That’s why it’s effective - it slows down the process. But here’s the catch: vitamin K doesn’t stay the same from day to day. A big salad one day, a serving of broccoli the next, even a different brand of multivitamin - all of these can throw your INR off. Your body needs vitamin K to make clotting factors, and warfarin fights that. When vitamin K levels swing, so does your INR.

Studies show people with unstable INRs are eating, on average, less than half the vitamin K of those with stable results. One 2007 study found that stable patients got about 293 micrograms of vitamin K daily. Unstable patients? Just 109. That’s not a coincidence. It’s a pattern.

The 150 mcg Solution

Instead of chasing your INR with bigger or smaller warfarin doses every week, some doctors are trying something different: giving you a small, steady dose of vitamin K - 150 micrograms a day. That’s about 1.5 times what the government says you should get from food, but still far below any dangerous level. It’s not a magic bullet, but it’s a steady hand on the wheel.

This isn’t about making your blood thicker. It’s about making your body’s response to warfarin more predictable. Think of it like this: if your warfarin dose is a faucet and vitamin K is water coming in from the side, you want the water flow to be constant. If the flow jumps up and down, you’ll have to keep adjusting the faucet - and you’ll never get it just right. A steady 150 mcg of vitamin K daily smooths out the flow.

Research from the Canadian multi-center trial in 2016 showed that this approach cut extreme INR spikes (above 4.5) and drops (below 1.5) by 4 percentage points. That might sound small, but for someone on warfarin, it means one fewer trip to the ER. In another study, patients on vitamin K had 54% more chance of achieving stable control than those who didn’t.

Who Should Try This?

This isn’t for everyone. If you have a mechanical heart valve in your mitral position, you need a higher INR target - and vitamin K could mess that up. If you’ve had a recent clot, stroke, or active cancer, you’re not a candidate either. The people who benefit most are those who:

• Have been on warfarin for months or years
• Have had at least 30% of their INRs outside the target range in the last 6 months
• Follow their warfarin dose exactly - no missed pills
• Have tried eating consistent amounts of vitamin K (leafy greens, broccoli, Brussels sprouts) and still can’t stabilize

It’s not about what you eat. It’s about what your body *expects*. If your vitamin K intake is unpredictable, your INR will be too. A daily 150 mcg supplement gives your body a baseline. Suddenly, your salad doesn’t matter as much.

What Happens When You Start?

You don’t start and feel better right away. It takes 4 to 8 weeks for the effects to show. In the first few weeks, your INR might drop - sometimes sharply. That’s normal. Your doctor will likely increase your warfarin dose by 0.5 to 1.5 mg during this time. Don’t panic. This isn’t failure - it’s adjustment.

In one case study, a 68-year-old man with an artificial aortic valve had 17 warfarin dose changes in 18 months. After starting 150 mcg of vitamin K daily, he had only two adjustments over the next six months. His INR stayed in range 71% of the time - up from 42%.

But it doesn’t always work. About 1 in 10 people see no improvement or even get worse. Why? Sometimes it’s because they’re still eating huge amounts of vitamin K - think 500 mcg or more a day from supplements or greens. That defeats the purpose. Other times, they’re skipping warfarin doses, and the vitamin K is hiding the problem.

Vitamin K vs. Other Options

You might be thinking: why not just switch to a DOAC like apixaban or rivaroxaban? Those don’t need INR checks at all. But here’s the reality: about 2 million Americans still need warfarin. Why? Because DOACs don’t work for people with mechanical heart valves, severe kidney disease, or antiphospholipid syndrome. For them, warfarin is the only option.

Compared to home INR monitors - which cost $500 to $1,000 and require training - vitamin K supplementation costs about 4 cents a day. A 5 mg bottle of generic vitamin K1 at Walgreens lasts over a year. No fancy device. No training. Just a tiny pill.

It’s not a replacement for monitoring. You still need your INR checked regularly. But it reduces the noise. Less fluctuation means fewer dose changes, fewer hospital visits, and less stress.

What Doctors Are Saying

Some experts are excited. Dr. Jacob Siegel at Johns Hopkins says the 4% drop in dangerous INR spikes translates to about 15 fewer risky values per patient per year. That’s a real safety gain.

Others are cautious. Dr. Daniel Witt, who helped write the official guidelines, warns that vitamin K might be masking bigger problems - like someone forgetting their warfarin or eating wild amounts of kale. He’s right. This isn’t a fix for poor habits. It’s a fix for unpredictable biology.

The European Heart Rhythm Association gives it a “may be considered” recommendation - Class IIb, Level B. That’s not a strong endorsement, but it’s not a no either. It’s a green light for careful use.

How to Get Started

If you think this might help you:

1. Talk to your hematologist or anticoagulation clinic. Don’t start on your own.
2. Make sure your INR history shows instability - at least 30% of readings outside target range.
3. Confirm you’re taking warfarin consistently - no missed doses.
4. Avoid other vitamin K supplements or high-dose multivitamins.
5. Ask for a 1-month baseline INR check before starting.
6. After starting, expect weekly INR checks for the first month, then every two weeks.
7. Be patient. It takes 4-8 weeks to see results.

Your doctor will likely increase your warfarin dose slightly. That’s okay. The goal isn’t to take less warfarin - it’s to make your dose work better.

What to Watch For

Side effects? Almost none. Vitamin K1 at this dose is safe. The only real risk is if you start it and then stop eating greens for a week - or start eating them like crazy. That’s when your INR will swing again.

Also, don’t confuse this with vitamin K2. The studies used K1 (phylloquinone). K2 (menaquinone) comes from fermented foods and supplements, but it’s not proven to help with warfarin. Stick to K1.

If after 3 months your INR is still all over the place, stop. This isn’t the answer for everyone. But for the right person - someone with consistent habits and stubborn instability - it can be life-changing.

The Future of Warfarin Management

Right now, only about 28% of U.S. anticoagulation clinics offer vitamin K supplementation. That’s changing. The American Heart Association now calls it a “promising practice.” A major trial called VIKING, expected to finish in late 2024, could push this into mainstream use.

One day, doctors might test your genes to see how your body responds to vitamin K. Then they’ll give you a custom dose. But for now, the simple, cheap, safe fix is already here: 150 mcg of vitamin K1 daily. For people stuck in the warfarin rollercoaster, it might be the steady hand they’ve been waiting for.