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Vitamin K2 Supplements: Warfarin, Bones, Arteries and D3 With K2

If you take warfarin, don't start, stop or change vitamin K2 without your anticoagulation clinic, and expect extra INR checks: as little as 10 mcg a day lowered the INR in volunteers on a similar drug (grade C). Apixaban, rivaroxaban, dabigatran and edoxaban don't work through vitamin K. For bones, K2 trials disagree (grade C) and the fracture benefit faded once retracted trials were removed. No trial shows K2 clears artery plaque.

Published How we grade evidenceEditorial policy

Vitamin K2 (menaquinone) is a family of vitamin K forms found in natto, a fermented soybean food, and in smaller amounts in cheese, meat and eggs (NIH ODS). Supplements sell it as MK-7 or MK-4. This guide covers adults.

If you take warfarin, don't start, stop or change a vitamin K2 supplement on your own. Vitamin K works against warfarin, so tell your anticoagulation clinic first and expect extra INR checks. Apixaban, rivaroxaban, dabigatran and edoxaban work differently.

The short version

  • Warfarin-type drugs: in healthy volunteers on acenocoumarol, which works like warfarin, MK-7 at 10 to 45 mcg a day lowered the INR, and the authors advise people on these drugs to avoid MK-7 supplements. Grade C (Theuwissen 2013). If your clinic agrees to any K2, keep the amount steady and expect extra INR checks.
  • Apixaban, rivaroxaban, dabigatran, edoxaban: their labels say vitamin K is not expected to affect (for edoxaban, not expected to reverse) their anticoagulant activity (apixaban label).
  • Bone density (women after menopause, MK-7 against placebo): 2 trials found less bone loss and 2 found none. Grade C, mixed (Knapen 2013; Rønn 2021).
  • Fractures: a big hip fracture benefit in older Japanese MK-4 trials became unclear once 3 retracted trials were removed. Grade C, not shown (Avenell 2019; Mott 2019).
  • Artery calcium (heart disease or high calcium scores, against placebo): scores rose in every group; 2 trials found a slower rise with K2 (with D3 in one), others no clear difference, and the trials were too small to judge heart attacks: the two that tracked heart events found no difference in one (10 against 10) and fewer in the other (1.9% against 6.7%), a result that needs testing. Grade C, mixed (Vossen 2026; Diederichsen 2022; Hasific 2023).
Question (who, compared with what)What trials foundSize of effectGrade
INR on a warfarin-type drug (15 healthy volunteers, rising MK-7 doses)INR fellAbout 40% lower at 45 mcg a dayC
Bone density (women after menopause, MK-7 vs placebo)Less loss in 2 trials, none in 2No difference over 3 years in 142 womenC, mixed
Hip fractures (Japanese MK-4 trials, retracted ones removed)No clear effectOdds ratio 0.30, range 0.05 to 1.74C
Coronary calcium (high scores, vs placebo, 2 years)Slower rise in 2 trials, not in others52 units less rise in 398 peopleC, mixed

Can I take vitamin K2 with warfarin?

Only with your anticoagulation clinic's agreement, and then at the same amount every day. Warfarin is a vitamin K antagonist: it blocks the vitamin K your liver uses to make clotting factors. Its label lists "increased vitamin K intake" as a cause of a lower INR response and asks for more frequent INR checks when you start or stop other products, botanicals included. It does not say to cut out vitamin K: it advises a normal, balanced diet with a consistent amount and no drastic changes (warfarin label). NIH ODS adds that sudden changes in vitamin K from food and supplements can raise or lower the drug's effect (NIH ODS).

Grade C: small K2 doses moved the INR. Eighteen healthy volunteers took acenocoumarol, and the 15 who reached an INR of 2.0 then added rising daily doses of MK-7 for 6 weeks. At 45 mcg a day, the group's INR fell by about 40%; at 10 and 20 mcg, two hematologists judged the drop clinically relevant in at least 40% and 60% of them (Theuwissen 2013); the authors concluded that MK-7 supplements need to be avoided by people on these drugs. MK-7 lasts far longer in the blood than vitamin K1, and an earlier study warned that 50 mcg a day or more may interfere with these drugs (Schurgers 2007). Natto, the richest food source, strongly opposed warfarin in people after heart valve surgery (Kudo 1990).

Steady is the goal, not zero. Some clinics add a small daily vitamin K dose on purpose when the INR swings for no clear reason: in a Cochrane review of 2 trials (100 people), one 70-person trial found 150 mcg a day improved control, the other (30 people) found no benefit, and the review judged the data insufficient to suggest an overall benefit (Mahtani 2014). That is the clinic's call, with INR checks. If you already take K2 on warfarin, don't stop it suddenly either, since stopping can push the INR up. The blood thinners guide covers other products that move the INR.

Can I take vitamin K2 with Eliquis, Xarelto or aspirin?

Apixaban (Eliquis), rivaroxaban (Xarelto), dabigatran and edoxaban don't work through vitamin K. The first three labels each say "protamine sulfate and vitamin K are not expected to affect the anticoagulant activity" of the drug, and the edoxaban label says vitamin K is "not expected to reverse" it. These drugs block clotting factor Xa or thrombin directly (apixaban label; rivaroxaban label; dabigatran label; edoxaban label). Still show your pharmacist the bottle, because blends often add ingredients that do matter with blood thinners, such as fish oil (can I take fish oil with Eliquis?).

No studies have tested K2 with aspirin, clopidogrel (Plavix) or statins. Aspirin and clopidogrel act on platelets, not vitamin K. Ask your prescriber or pharmacist before you add it.

Does vitamin K2 thin your blood or cause clots?

It does not thin blood, and in a year-long trial it did not make blood clot more (grade C). Vitamin K helps make clotting factors (NIH ODS). In 123 people on dialysis, 360 mcg of MK-7 a day for 52 weeks showed no difference from placebo in clotting tests or adverse events (Bladbjerg 2024). On warfarin the risk runs the other way: K2 can weaken your protection against clots.

Does vitamin K2 help bones and osteoporosis?

Grade C, mixed for bone density; fewer fractures not shown. Four placebo-controlled K2 trials that included women after menopause split two ways:

  • Less loss: 244 healthy women taking 180 mcg a day for 3 years lost less bone density at the lower spine and femoral neck (top of the thigh bone), though not at the total hip (Knapen 2013). In 311 Chinese adults aged 50 to 75, 90 mcg a day for a year slowed femoral neck loss in women but not in men, and adding calcium and vitamin D3 gave no extra effect (Zhang 2020).
  • No difference: 334 Norwegian women in early menopause took 360 mcg a day as natto capsules for a year (Emaus 2010). And 142 women with osteopenia (thinner bones than normal, not yet osteoporosis) took 375 mcg a day for 3 years on top of calcium and vitamin D3; bone density fell alike in both groups (Rønn 2021).

The vitamin K2 page shows B, "improves", for spine and hip bone density; with half these trials finding no difference, C fits better.

The fracture evidence weakened after retractions. In Japan, a medicine dose of MK-4 (45 mg a day) is used for osteoporosis (NIH ODS). A 2006 pooling of 7 Japanese MK-4 trials reported far fewer hip fractures (odds ratio 0.23), but three of those trials came from the group of Yoshihiro Sato, whose trial reports were later retracted for research misconduct; without them the hip result was no longer clear (odds ratio 0.30, range 0.05 to 1.74), and the review's authors issued a caution and a corrected article (Avenell 2019; Torgerson 2018). A statistical check of that group's 33 trials had found improbably similar treatment groups and hip fracture drops far larger than other trials report (Bolland 2016).

Newer reviews are weaker. An update of 36 trials found no effect on bone density or spine fractures; a possible drop in any clinical fracture was not clear in the better-run (low risk of bias) trials (Mott 2019), and a 2020 correction then adjusted its figures after doubts about another Japanese trial, YOPS (Mott 2020), which was retracted in 2025 (retraction notice). In the largest MK-4 trial, 4,378 women with osteoporosis on calcium had no fewer new spine fractures over 3 years with MK-4 added (Inoue 2009). K2 is not a stand-in for an osteoporosis medicine; see osteoporosis and which supplements help bone density?

Does vitamin K2 remove plaque from arteries?

No trial shows that it removes plaque. For slowing calcium build-up, grade C, mixed. Most trials measured calcium in the heart arteries on CT scans, and it kept rising in both groups:

  • Slower rise: in 180 people with coronary artery disease causing symptoms, 360 mcg of MK-7 a day for 2 years: scores went from 135 to 184 on MK-7 and from 145 to 214 on placebo. What this means for plaque stability and heart events is unknown (Vossen 2026). In 398 people with severe calcium, K2 (720 mcg) plus vitamin D3 daily for 2 years: scores rose 196 units against 248, while total plaque volume grew alike in both groups (Hasific 2026).
  • No clear difference: in 304 men without heart disease on the same K2 plus D3: a rise of 203 against 254 units (Hasific 2023). In 365 men with a calcified aortic valve: valve calcium, surgery, deaths and heart events did not differ (Diederichsen 2022). In 68 people with type 2 diabetes and heart disease, a PET scan showed a trend, not statistically clear, toward more active calcification after 6 months of MK-7 (Zwakenberg 2019).
  • Kidney disease: pooling 10 trials (733 people), vitamin K lowered blood markers and eased artery stiffness a little but did not change calcium scores (Geng 2023). The vitamin K page shows D for this; a pooled analysis of 10 trials supports C.

Pooling 14 trials (1,533 people) found a small slowing of coronary calcium, about 17 units (Li 2023). A Cochrane review found only one 3-month trial in 60 healthy people, which did not report heart events (Hartley 2015). K2 reliably lowers dp-ucMGP and inactive osteocalcin, blood markers of unused vitamin K-dependent proteins in arteries and bone. These lab markers are not evidence of stronger bones or cleaner arteries, which is why the clinical claims here are graded C at most (Diederichsen 2022; Rønn 2021); the K2 page's A for osteocalcin and B for matrix Gla protein describe blood tests, not stronger bones or cleaner arteries. See coronary artery disease.

Do you need vitamin K2 with vitamin D3?

No trial shows that you do. The claim is that K2 steers calcium into bone. In the 3-year trial above, adding 375 mcg of MK-7 to vitamin D3 and calcium did not change bone density (Rønn 2021). No trial has compared D3 alone with D3 plus K2 for artery calcium or heart events, and none shows K2 makes vitamin D above the adult upper limit safer. For adults that limit is 4,000 IU (100 mcg) a day, since higher intakes can push blood calcium too high; go above it only after blood tests and your clinician's advice (NIH ODS; check your stack). See vitamin D supplements and calcium.

MK-4 or MK-7, and how much vitamin K2 a day?

NIH sets no upper limit, which is not proof that any amount is safe: trials used up to 720 mcg of MK-7, and on warfarin even 10 mcg matters. NIH ODS says the Food and Nutrition Board set none "because of its low potential for toxicity", noting that "no adverse effects associated with vitamin K consumption from food or supplements have been reported in humans or animals" (NIH ODS). The adequate intake for all vitamin K together is 120 mcg a day for adult men and 90 mcg for adult women.

  • MK-7: bone trials used 90 to 375 mcg a day; artery trials 360 to 720 mcg.
  • MK-4: the Japanese osteoporosis trials used the 45 mg medicine dose. At food-level doses MK-4 barely registers: in healthy Japanese women, a 420 mcg dose of MK-4 was not detectable in the blood, while MK-7 was absorbed and lasted up to 48 hours. Grade C, blood levels only (Sato 2012).
  • Timing: vitamin K is absorbed along with fat from food (NIH ODS), so many people take it with a meal. No trial has compared times of day.

Does vitamin K2 help leg cramps, blood sugar or arthritis?

  • Night leg cramps: grade D. In a single trial, 199 people aged 65 or over reported fewer night cramps after 8 weeks of 180 mcg MK-7, and in 2025 the journal replaced the paper with a corrected version, a retraction and replacement for errors (Tan 2024, replaced; notice). See supplements for leg cramps.
  • Blood sugar: grade C. In 8 trials of people with prediabetes or type 2 diabetes, vitamin K lowered fasting sugar, HbA1c (by about 1 percentage point, with wide uncertainty) and insulin resistance, but not insulin; the trials mixed vitamins K1, K2 and K4, and the authors call them few and of moderate quality (Ahmed 2026). Don't skip or swap a diabetes medicine for it, and check your sugar more often if you add it.
  • Arthritis: grade C, no effect, for vitamin K1 only. In 378 older adults, vitamin K1 for 3 years did not change hand osteoarthritis on X-rays (Neogi 2008). No trial has tested K2 for osteoarthritis.

What we'd skip

  • K2 to "clear" arteries: calcium rose in every trial group, and the trials were too small to judge heart attacks (Vossen 2026; Hasific 2023; Hartley 2015).
  • K2 in place of an osteoporosis medicine: the fracture benefit did not hold up once flawed trials were removed (Avenell 2019; Inoue 2009).
  • K2, natto or a D3 plus K2 blend on warfarin without the clinic: 10 mcg a day moved the INR in some volunteers (Theuwissen 2013).

Safety and interactions

  • Warfarin, acenocoumarol, phenprocoumon: K2 can weaken them, raising the risk of clots and stroke; keep intake steady and tell your clinic before any change (NIH ODS).
  • Medicines that lower vitamin K: long antibiotic courses, bile acid sequestrants such as cholestyramine, and orlistat; orlistat with warfarin may raise prothrombin time, a clotting test (NIH ODS).
  • Side effects: a US Pharmacopeia review found MK-7 supplements not linked to any serious risk to health (Marles 2017). In the largest trial of the MK-4 medicine dose, in 4,378 women with osteoporosis, adverse events and adverse reactions were more frequent when MK-4 was added to calcium (Inoue 2009).
  • Kidney disease: ask your kidney team before adding any supplement; see the chronic kidney disease protocol.
  • Pregnancy and breastfeeding: K2 supplements have not been studied enough; take one only if your midwife or obstetric team advises it. For children, ask your child's doctor.
  • Blends: many D3 plus K2 products add calcium; check your stack for vitamin D and calcium totals.

When to see a doctor

  • Call emergency services for signs of a clot or stroke: one leg swollen, warm or painful; chest pain or sudden breathlessness; face drooping, a weak arm or slurred speech. This matters most on warfarin after starting, stopping or changing K2.
  • Call your anticoagulation clinic the same day on warfarin for unusual bruising, bleeding gums, nosebleeds, pink or brown urine, black or bloody stools, or an INR out of range after a change in K2 or natto.
  • Ask about a bone density scan if you break a bone in a minor fall, get sudden back pain or lose height.

Don't stop a prescribed medicine on your own; ask the prescriber or pharmacist. If you're under 18, ask a clinician; if you're pregnant or breastfeeding, your midwife or obstetric team should advise you.

FAQ

Does vitamin K2 affect warfarin? Yes. Vitamin K works against warfarin, and MK-7 at 10 to 45 mcg a day lowered the INR in healthy volunteers taking acenocoumarol, a warfarin-like drug (grade C). Take it only with your anticoagulation clinic's agreement, at a steady daily amount, with INR checks.

Can I take vitamin K2 with Eliquis or Xarelto? Their labels say vitamin K is not expected to affect how apixaban or rivaroxaban works, because they block factor Xa rather than vitamin K. Still tell your prescriber or pharmacist about every supplement you take.

Does vitamin K2 remove plaque from arteries? No trial shows it. Heart artery calcium kept rising in every group; 2 trials in people with heart disease or high calcium found a slower rise with K2, others found no clear difference (grade C), and the trials were too small to judge heart attacks.

Is vitamin K2 good for your bones? Results are mixed. Two of 4 placebo-controlled MK-7 trials in women after menopause found less bone loss (grade C), and the fracture benefit from older Japanese MK-4 trials became unclear once retracted trials were removed (grade C).

Do I need to take vitamin K2 with vitamin D3? No trial shows you do. Adding MK-7 to vitamin D3 and calcium for 3 years did not change bone density in 142 women with osteopenia (grade C).

Sources

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