Vitamin K Supplements and Warfarin: How to Keep INR Stable

If you're on warfarin, you know how unpredictable your INR levels can be. One week you're perfect, the next you're bleeding or clotting, and your doctor keeps changing your dose. It’s exhausting. But what if the problem isn’t your warfarin dose at all? What if it’s your vitamin K intake?

Why Your INR Fluctuates

Warfarin works by blocking vitamin K from helping your blood clot. That’s why it prevents dangerous clots. But here’s the catch: vitamin K isn’t just in supplements. It’s in spinach, kale, broccoli, Brussels sprouts, and even some oils. One day you eat a big salad, your INR drops. The next day you skip greens, your INR spikes. That’s why so many people on warfarin have unstable INR levels-between 30% and 50% of them, according to the American Heart Association.

It’s not about eating too much or too little vitamin K. It’s about inconsistency. Your body needs a steady amount. If you’re swinging between 50 mcg one day and 500 mcg the next, your warfarin dose can’t keep up. That’s where low-dose vitamin K supplementation comes in-not to fight warfarin, but to smooth out the ride.

The 150 mcg Solution

Research shows that taking 150 micrograms (mcg) of vitamin K1 daily can make a real difference. That’s about 1.5 times the daily recommended intake for adults, but still far below any toxic level. This dose doesn’t change your warfarin’s effect-it just gives your body a consistent baseline.

A 2007 study in Blood found that patients who took 150 mcg daily had much more stable INR levels than those who didn’t. Their INR swings dropped by nearly half. Another study in 2016, done across Canadian clinics, confirmed it: patients on vitamin K supplements had 4% fewer dangerous INR spikes (above 4.0) or crashes (below 1.5). That might sound small, but in real terms, it means one fewer emergency visit per patient per year.

This isn’t magic. It’s physics. Think of your INR like water in a bucket. Warfarin is the drain. Vitamin K from food is the faucet-sometimes it’s wide open, sometimes it’s dripping. Adding a steady drip of 150 mcg vitamin K every day? That’s like installing a small, constant trickle. Now the water level stays even, even if the faucet changes.

Who Benefits Most

Not everyone on warfarin needs this. If your INR is consistently between 2.0 and 3.0, you’re fine. But if you’re one of the 30-50% with wild swings, and you’ve already tried eating the same amount of greens every day, this might be your next step.

Good candidates usually have:

• TTR (Time in Therapeutic Range) under 65% over six months
• Three or more INR values above 4.0 or below 1.5 in the past year
• No major dietary changes (like suddenly eating a lot of kale)
• No mechanical heart valves in the mitral position (those need higher INR targets)

People with kidney disease on dialysis, or those with antiphospholipid syndrome, often benefit the most. Their bodies handle vitamin K differently, and warfarin becomes extra unpredictable.

What Happens When You Start

Don’t expect instant results. It takes 4 to 8 weeks for your INR to settle. In the first two weeks, your INR might actually drop. That’s normal. Your body is adjusting to the steady vitamin K. Your doctor will likely increase your warfarin dose slightly-by 0.5 to 1.5 mg-to compensate. In one study, the average warfarin dose went from 4.8 mg to 5.4 mg daily after starting vitamin K.

Monitoring stays critical. You’ll still need weekly INR checks for the first month, then every two weeks. Don’t assume you’re stable just because you’re taking vitamin K. The goal isn’t to stop testing-it’s to make your test results less scary.

What It Doesn’t Do

Vitamin K won’t fix everything. If you’re skipping your warfarin pills, it won’t help. If you’re suddenly eating a whole head of kale every day, it won’t help. If you’re on a new antibiotic or herbal supplement that interferes with warfarin, it won’t help. It’s not a band-aid. It’s a tool for people who are already doing everything right-except keeping their vitamin K steady.

It also doesn’t replace DOACs like apixaban or rivaroxaban. Those drugs don’t need INR monitoring at all. But for people with mechanical heart valves or certain clotting disorders, warfarin is still the only option. That’s where vitamin K supplementation shines.

Cost and Accessibility

This is one of the cheapest interventions in medicine. A 5 mg bottle of vitamin K1 (phylloquinone) costs about $8 at Walgreens. That’s 100 tablets. You only need 150 mcg per day-that’s one-third of a tablet. So you’re paying less than half a cent per day.

It’s available over the counter. No prescription needed. But don’t just buy any supplement. Look for phylloquinone (vitamin K1), not menaquinone (K2). K2 doesn’t work the same way with warfarin. And avoid multivitamins with high doses of K-stick to the 150 mcg dose.

What Doctors Say

Some doctors are hesitant. The American College of Chest Physicians says the evidence isn’t strong enough for a formal recommendation. But others are convinced. Dr. Jacob Siegel at Johns Hopkins says the 4% drop in dangerous INR excursions means about 15 fewer high-risk readings per patient each year. That’s enough to prevent strokes or major bleeds.

Dr. Elaine Hylek from Boston University calls it “one of the most promising approaches” to warfarin stability. And in Europe, the 2020 Heart Rhythm Association guidelines give it a “may be considered” recommendation-Class IIb, Level B.

The big shift is coming. In 2023, the American Heart Association added vitamin K supplementation to its “promising practices” list for warfarin patients. If results from the ongoing VIKING trial (expected late 2024) confirm the benefits, this could become standard care by 2026.

Real Patient Stories

One man, 68, with a mechanical aortic valve, had an INR TTR of just 42% over 18 months. He was constantly adjusting his warfarin. After starting 150 mcg vitamin K daily, his TTR jumped to 71% in six months. He needed only two dose changes instead of 17.

Another patient, on Reddit, said her INR was a rollercoaster for eight years. After vitamin K, her TTR went from 55% to 78%. She went from 11 INRs over 4.0 in six months to just two.

But not everyone wins. Some patients see no change. A few even get worse. That’s why it’s not for everyone. If your INR doesn’t improve after three months, stop it. There’s no point forcing it.

How to Start

If you think this might help you:

1. Track your INR for six months. If your TTR is below 65%, talk to your hematologist or anticoagulation clinic.
2. Ask if they’ve used vitamin K supplementation before. Most clinics now have protocols.
3. If they agree, get 150 mcg of phylloquinone (vitamin K1). Buy it as a standalone tablet, not in a multivitamin.
4. Take it at the same time every day-preferably with food, since it’s fat-soluble.
5. Keep your diet consistent. Don’t suddenly start eating a lot of greens or stop.
6. Stick to your INR checks. Don’t skip them, even if you feel fine.

And if your doctor says no? Ask why. If it’s because “there’s no evidence,” show them the 2016 Canadian trial or the 2022 systematic review in Blood Advances. This isn’t fringe science anymore. It’s becoming standard.

The Bigger Picture

Warfarin is old, but it’s not going away. Over 2 million Americans still rely on it. And for many, it’s the only option. Vitamin K supplementation doesn’t replace it. It makes it work better.

It’s not about taking more of something. It’s about taking the right amount, every day. That’s the secret to stable INR. Not luck. Not guesswork. Just consistency.

If you’ve been stuck in the warfarin rollercoaster, this might be your way off. But only if you’re ready to make it part of your routine-every day, without fail.