INR Stability Calculator

How Vitamin K Affects Your INR

Your INR fluctuates because of inconsistent vitamin K intake. This calculator shows how your INR might vary based on your typical vitamin K consumption pattern, and how taking 150 mcg of vitamin K daily can stabilize it.

Note: This is a simplified visualization based on clinical studies. Your actual INR response may vary. Always follow your doctor's advice.
Your Vitamin K Intake Pattern

How much vitamin K do you typically consume each week?

1 serving = about 1 cup of leafy greens
E.g., if you eat leafy greens 4 days/week, enter 3 for days without
INR Stability Comparison

Enter your vitamin K intake pattern above to see the comparison

Understanding Your INR Levels

1.8-2.5 (Therapeutic Range)
2.5-3.5 (Increased Bleeding Risk)
>3.5 (High Bleeding Risk)

For people on warfarin, the target INR range is typically 2.0-3.0 (or higher for some conditions). INR levels outside this range increase your risk of bleeding or clots.

If you're on warfarin, you know how frustrating it can be when your INR jumps around for no obvious reason. One week you're in range, the next you're either too high and at risk of bleeding, or too low and vulnerable to clots. For many people, this rollercoaster isn't caused by missing a dose or eating too much kale-it's because their body is getting inconsistent amounts of vitamin K from day to day. That’s where low-dose vitamin K supplements come in. Not as a replacement for warfarin, but as a tool to smooth out the bumps.

Why Your INR Keeps Fluctuating

Warfarin works by blocking vitamin K’s role in making blood clotting proteins. But vitamin K doesn’t just come from pills-it’s in your food. Leafy greens, broccoli, Brussels sprouts, and even some oils are packed with it. If you eat a big salad on Monday and nothing green on Wednesday, your vitamin K levels swing. That makes warfarin’s effect unpredictable. Your INR drops after eating vitamin K-rich food, then rises again when you skip it. This is why 30 to 50% of people on warfarin struggle with unstable INR, even when they take their pill exactly as prescribed.

The key isn’t avoiding vitamin K. It’s keeping it steady. That’s the whole idea behind taking 150 micrograms of vitamin K1 daily-a dose proven in multiple studies to reduce wild INR swings. It’s not about making your blood thicker or thinner. It’s about giving your body a consistent baseline so warfarin can do its job without fighting your diet.

How Much Vitamin K Should You Take?

The magic number is 150 micrograms per day. That’s not a high dose. The recommended daily intake for adults is 90-120 mcg depending on sex. So 150 mcg is just a little above normal, well under the safety limit of 10,000 mcg per day. You won’t overdose. You won’t feel different. You won’t start clotting uncontrollably.

This dose comes from years of research. The landmark 2007 study by Sconce et al. showed that people with unstable INR had far lower vitamin K intake than those with stable control. When they gave 150 mcg daily to unstable patients, nearly 60% saw big improvements. Later trials, like the Canadian multi-center study in 2016, confirmed this: extreme INR spikes (above 4.5) dropped from 9.4% to 5.4% with daily vitamin K. That’s a 4% absolute reduction in dangerous events-meaning fewer hospital visits, fewer bleeds, fewer clots.

It’s not a cure-all. It won’t fix poor adherence, drug interactions, or liver problems. But if your INR keeps bouncing for no clear reason, and your diet is already consistent, vitamin K supplementation might be the missing piece.

What Happens When You Start Taking It?

Don’t expect instant results. Vitamin K doesn’t work like a fast-acting drug. It takes 4 to 8 weeks for your body to adjust. In the first few weeks, your INR might dip lower than usual. That’s normal. Your liver is getting a steady supply of vitamin K, so warfarin’s effect becomes more predictable-but that also means you may need a higher warfarin dose to stay in range.

Most patients end up increasing their warfarin dose by 0.5 to 1.5 mg per day after starting vitamin K. That sounds scary, but it’s not. You’re not becoming resistant. You’re just balancing out the extra vitamin K your body now gets daily. Your doctor will adjust your warfarin based on your INR readings, just like before-but now the changes will be smaller and less frequent.

One patient, a 68-year-old man with a mechanical heart valve, had 17 warfarin dose changes over 18 months. After starting 150 mcg vitamin K daily, he had only two adjustments in the next six months. His INR stayed in range 71% of the time-up from 42%. That’s the kind of difference this can make.

A patient with a holographic INR graph and vitamin K1 as steady golden threads balancing warfarin pulses inside their body.

Who Shouldn’t Take Vitamin K With Warfarin?

This isn’t for everyone. If you have a mechanical heart valve in your mitral position, your target INR is higher (2.5-3.5), and adding vitamin K could push you out of range. If you’ve had a recent clot, stroke, or are undergoing cancer treatment, you’re not a candidate. These groups were excluded from all major studies.

Also, don’t start this if you’re already eating more than 500 mcg of vitamin K a day. That’s like eating two cups of cooked kale daily. If your diet is already high and erratic, adding a supplement won’t help-it’ll make things worse. The goal is consistency, not overload.

And if your INR problems are caused by missing doses, drinking alcohol heavily, or taking antibiotics that interfere with warfarin, vitamin K won’t fix that. You need to fix the root cause first.

How It Compares to Other Options

Many people wonder: why not just switch to a DOAC like apixaban or rivaroxaban? Those don’t need INR checks. That’s true-but DOACs aren’t right for everyone. If you have a mechanical valve, antiphospholipid syndrome, or severe kidney disease, warfarin is still your best or only option. About 2 million Americans still rely on it.

Point-of-care INR monitors let you test at home, but they cost $500-$1,000 and require training. Vitamin K costs less than a penny a day. A 5 mg bottle of generic vitamin K1 at Walgreens lasts over 300 days. No device. No app. No hassle.

Compared to frequent doctor visits and emergency trips, vitamin K is cheap, simple, and low-risk. It doesn’t replace monitoring-you still need regular INR tests-but it makes those tests far less stressful.

A battlefield in the bloodstream where a vitamin K1 mech calms chaotic kale explosions, creating stable clotting waves.

What Your Doctor Needs to Know

Not all doctors know about this approach. A 2022 survey found only 28% of anticoagulation clinics in the U.S. offer vitamin K supplementation. But it’s gaining traction. The American Heart Association now lists it as a “promising practice.” The European Heart Rhythm Association gives it a Class IIb recommendation-meaning it’s reasonable to try in selected patients.

If you’re interested, bring up the research. Ask if your INR instability qualifies you for this. Most clinics follow a simple protocol: check your TTR (time in therapeutic range) over the past 6 months. If it’s below 65%, and you’ve ruled out dietary chaos or medication issues, vitamin K is worth a trial.

Be prepared to explain why you’re taking a “clotting vitamin” while on a blood thinner. Use this analogy: imagine your blood clotting system is a bucket. Warfarin is a hole at the bottom letting water out. Vitamin K is water coming in from a hose. If the hose flow changes every day, the bucket level swings wildly. But if you turn the hose on at a steady drip, the bucket stays full-and the water draining out becomes predictable. That’s what vitamin K does.

Real Results, Real People

On Reddit’s r/Warfarin community, users report real changes. One person said after 8 years of unstable INRs (55% TTR), adding 150 mcg vitamin K daily lifted their TTR to 78%. Another saw their dangerous INR spikes drop from 11 in six months to just two.

But it doesn’t work for everyone. About 10% of users in the Anticoagulation Forum’s database saw no improvement-or worse. One woman’s TTR dropped from 58% to 49% after starting vitamin K. That’s why it’s not a one-size-fits-all fix. It’s a targeted tool for a specific problem: unexplained INR variability.

The bottom line? If you’re on warfarin and your INR won’t stay steady, despite doing everything right, ask your doctor about vitamin K. It’s not magic. But for the right person, it’s one of the simplest, cheapest, and safest ways to take back control.

What to Do Next

If you think this might help you:

  1. Review your last 6 months of INR logs. Are you spending less than 65% of the time in range?
  2. Have you ruled out dietary swings, alcohol, or new medications?
  3. Do you have a mechanical heart valve in the mitral position? If yes, skip this.
  4. Ask your anticoagulation clinic if they offer vitamin K supplementation.
  5. If they say yes, start with 150 mcg of vitamin K1 daily. Keep taking your warfarin as usual.
  6. Expect your INR to dip in the first 2-4 weeks. Don’t panic. Don’t skip your warfarin.
  7. Get your INR checked weekly for the first month, then every two weeks.
  8. Your warfarin dose may need to go up slightly. That’s okay.
  9. Give it 8 weeks before judging results.

If you don’t see improvement after 3 months, stop. It’s not for everyone. But if it works? You might finally sleep through the night without worrying about your next INR test.

Can I just eat more leafy greens instead of taking a vitamin K supplement?

No. Eating more greens won’t help if your intake is already inconsistent. The goal isn’t to increase vitamin K-it’s to make it predictable. A supplement gives you the exact same dose every day. Leafy greens vary wildly in vitamin K content. A cup of spinach one day might have 145 mcg; a cup of kale the next might have 547 mcg. That’s why supplements work: they remove the guesswork.

Will vitamin K make my blood thicker and increase my risk of clots?

No. At 150 mcg per day, vitamin K doesn’t override warfarin. It just balances it. Think of it like adjusting the thermostat. You’re not turning up the heat-you’re keeping the temperature steady so the system works better. Studies show no increase in clots or strokes with this dose. In fact, fewer extreme INR excursions mean fewer clots.

Can I take vitamin K2 instead of K1?

No. All research on INR stabilization uses vitamin K1 (phylloquinone), found in green vegetables. Vitamin K2 (menaquinone), found in fermented foods and supplements, has a different effect on clotting factors and hasn’t been studied for this purpose. Stick with K1.

How long do I need to take vitamin K?

As long as you’re on warfarin. Vitamin K supplementation isn’t a short-term fix-it’s a long-term strategy for stability. If you stop taking it, your INR will likely become unpredictable again. But if you switch to a DOAC, you can stop vitamin K. It’s only needed for vitamin K antagonist therapy.

Is it safe to buy vitamin K over the counter?

Yes, but check the label. Look for vitamin K1 (phylloquinone), not K2. Avoid multi-vitamins with vitamin K-they often contain too little or too much, and the dose isn’t precise. Buy a standalone 1 mg (1000 mcg) tablet and cut it into 1/6th pieces (150 mcg). Or ask your pharmacist for a 150 mcg capsule. Generic brands are fine.

Will vitamin K interact with my other medications?

It’s unlikely to interact directly. But any new medication-even antibiotics, NSAIDs, or herbal supplements-can affect warfarin. Always tell your doctor you’re taking vitamin K. It doesn’t change how you monitor for interactions. You still need to watch for drugs that boost or weaken warfarin. Vitamin K just makes your response to warfarin more consistent.

Can I take vitamin K if I have liver disease?

Not without close supervision. Liver disease affects how your body processes both warfarin and vitamin K. If you have cirrhosis or severe liver impairment, your INR may be unstable for reasons beyond vitamin K. Adding vitamin K could mask the real problem. Talk to your hematologist first.

What if my INR drops too low after starting vitamin K?

Don’t panic. This is common in the first few weeks. Your doctor will likely increase your warfarin dose by 0.5-1.5 mg per day. That’s normal. It doesn’t mean the vitamin K isn’t working-it means it’s working exactly as intended. Your body is now getting consistent vitamin K, so warfarin needs to be stronger to keep you in range. Keep testing your INR and follow your doctor’s adjustments.