Vitamin K2 activates two proteins that put calcium into bone and keep it out of artery walls, which is why it is sold as the partner to vitamin D: vitamin D raises how much calcium you absorb, and K2 is meant to direct where that calcium goes. The mechanism is well established; the clinical evidence is more limited than the marketing suggests.
A modest 180 mcg daily dose of the MK-7 form slowed bone loss and improved a measure of arterial stiffness in postmenopausal women over three years, the food evidence for the heart is observational, and the randomized trials of arterial and valve calcification have so far found nothing. Get K2 from food first, add a modest MK-7 supplement if your diet is short of fermented and animal sources, and if you take warfarin or another blood thinner, do not start one without the prescriber who manages your INR.
Findings & Outcomes
What It Is
Vitamin K comes in two forms, and K2 is the one that works with calcium in bone and blood vessels. Vitamin K1 (phylloquinone) comes from green leaves and mostly goes to the liver, where it activates the clotting factors. Vitamin K2 (the menaquinones) comes from bacteria, from fermentation, and from animal tissue, and it reaches bone and the artery walls, where it activates the calcium-handling proteins described below. Two menaquinones account for the interest in K2: MK-4, made in animal tissue and used in Japan as a high-dose osteoporosis drug, and MK-7, made by bacteria and richest in the fermented soybean dish natto.
Anatomy of the Practice
1From animal food and fermentation
K2 reaches you from two routes: animal foods carry MK-4, and bacterial fermentation makes the longer menaquinones, above all the MK-7 concentrated in natto. Gut bacteria make some as well. This is a different source from the K1 in leafy greens, so a diet can be adequate in one form and low in the other.
2Activating the calcium proteins
In the liver and then in bone and vessel tissue, vitamin K lets an enzyme add carbon groups to specific proteins, a step called carboxylation. That step is what turns osteocalcin and matrix Gla protein from inactive to active. Without enough K2, a fraction of these proteins stays uncarboxylated and cannot do its calcium job.
3Directing where calcium settles
Activated osteocalcin binds calcium into the bone matrix; activated matrix Gla protein sits in artery walls and blocks calcium from depositing there. This is the basis of pairing K2 with vitamin D: vitamin D raises how much calcium you absorb, and K2 is proposed to direct where that calcium ends up.
How It Works
The carboxylation described above is well established. Turning that biochemical step into fewer broken bones or fewer heart attacks is a different question, and it is where vitamin K2 gets oversold.
Activating a protein is a measured biochemical change; preventing a fracture or a heart attack is a clinical outcome, and they are not the same result.
Whether the mechanism reaches those outcomes is what the trials below were built to test, and their answers are mixed. For the nutrient that raises calcium absorption in the first place, see vitamin D; for the strongest way to build the bone this is meant to protect, see resistance training.
What The Trials Found
The findings sort by outcome, bone and heart, and within each they run from a measured biochemical change toward the clinical events people want changed.
The firmest bone result is Knapen's three-year randomized trial: 244 healthy postmenopausal women took 180 mcg a day of MK-7, which slowed the age-related loss of bone mineral density at the spine and femoral neck and improved calculated measures of bone strength against placebo. That trial measured bone density on a scan, not broken bones. A much larger pharmacological dose of MK-4, 45 mg a day, is licensed in Japan as an osteoporosis treatment, and a meta-analysis of 13 trials found it reduced vertebral, hip and other fractures.
That pooled fracture result leans heavily on Japanese MK-4 trials, several of them methodologically weak, at a dose hundreds of times any nutritional amount, and it has not reproduced in that form elsewhere. Not every vitamin K result is positive: the ECKO trial gave 440 women with osteopenia 5 mg a day of vitamin K1 for two to four years and found no protection of bone density. So the bone case is modest: firmest at the surrogate of bone density, weaker the closer it gets to fractures.
For the heart, the divide is between what people eat and what trials have tested. In the Rotterdam Study, adults eating the most dietary K2, largely from cheese and meat, had lower coronary heart disease death and less severe aortic calcification than those eating the least, while dietary K1 showed no such link. That is an association: people who eat more of these foods differ in other ways, so it cannot show the K2 did the work.
The randomized trials that tried to confirm it have not. MK-7 at 360 mcg a day for six months did not slow arterial calcification in people with type 2 diabetes, and 720 mcg a day plus vitamin D for two years did not slow aortic valve calcification in older men. The one positive cardiovascular signal is softer: in Knapen's bone cohort, the same 180 mcg MK-7 improved arterial stiffness over three years, a surrogate measure, not a count of heart attacks or strokes.
K2 has a clear mechanism, a modest bone result at a nutritional MK-7 dose, an observational heart association, and calcification trials that have so far come back null.
The Research & Studies
Everything here is based on the research we have collected and checked, sorted into groups and ordered with the strongest evidence first. Click any claim to open the studies behind it.
Bone Density
180 mcg of MK-7 daily slowed bone loss over 3 years in postmenopausal women
Taking a modest daily dose of the MK-7 form of vitamin K2 for three years slowed bone loss in healthy postmenopausal women.
Knapen 2013 (Osteoporos Int) randomized 244 healthy postmenopausal women to 180 mcg/day MK-7 (menaquinone-7) or placebo for 3 years. MK-7 significantly reduced the decline in bone mineral density at the lumbar spine and femoral neck (not the total hip) and improved bone-strength indices derived from geometry, alongside a large rise in carboxylated osteocalcin. Actual fractures were not an endpoint, so the result is a slower loss on bone densitometry, not a demonstrated reduction in broken bones.
Who this may not transfer to:Tested only in postmenopausal women; whether the same MK-7 dose slows bone loss in men or younger adults has not been measured.
The study · 1
Knapen 2013, Osteoporos Int · Osteoporos Int
5 mg of vitamin K1 daily did not protect bone density in women with osteopenia (ECKO)
A large trial of high-dose vitamin K1 in women with thinning bones did not preserve bone density. Not every form of vitamin K and every outcome shows a benefit.
Cheung 2008 (PLoS Med), the ECKO trial, randomized 440 postmenopausal women with osteopenia to 5 mg/day vitamin K1 (phylloquinone) or placebo for 2 to 4 years. There was no protective effect on bone mineral density at the lumbar spine or total hip, the primary bone endpoints. Secondary analyzes found fewer clinical fractures (nine versus 20) and fewer cancers (three versus 12) in the K1 arm, but the trial was not powered for these, the numbers were small, and they need confirmation. The trial tested K1, not K2, in women with osteopenia rather than established osteoporosis.
Who this may not transfer to:ECKO enrolled postmenopausal women with osteopenia; the K1 bone-density result has not been tested in men.
The study · 1
Cheung 2008, PLoS Med (ECKO) · PLoS Med
45 mg of MK-4 daily cut fractures, mostly in Japanese osteoporosis trials
A prescription-strength MK-4 dose used in Japan reduced fractures in women with osteoporosis, but the evidence rests mostly on Japanese trials of variable quality and a dose far above any supplement.
Cockayne 2006 (Arch Intern Med) pooled 13 RCTs of vitamin K (7 reporting fractures) and found supplementation associated with reduced vertebral, hip and all nonvertebral fractures; the fracture data were dominated by Japanese trials of high-dose MK-4 (menatetrenone). The representative RCT, Shiraki 2000 (J Bone Miner Res), an open-label study, gave 45 mg/day MK-4 to 241 patients with osteoporosis and reported fewer new clinical fractures and sustained lumbar bone mineral density versus control. The dose is roughly hundreds of times a nutritional amount and licensed as a drug in Japan; several pooled trials had methodological limitations and the fracture benefit has not reproduced at this form and dose outside that setting.
Who this may not transfer to:The MK-4 osteoporosis trials enrolled postmenopausal women; the high-dose fracture benefit has not been tested in men.
The studies · 2
Cockayne 2006, Arch Intern Med · Arch Intern Med
Shiraki 2000, J Bone Miner Res · J Bone Miner Res
Heart And Vascular
MK-7 supplements did not slow artery or heart-valve calcification in randomized trials
When tested head to head, vitamin K2 supplements did not slow the buildup of calcium in arteries or heart valves in the trials done so far.
Two randomized trials tested whether MK-7 slows calcification. Zwakenberg 2019 (Am J Clin Nutr) gave 68 people with type 2 diabetes and cardiovascular disease 360 mcg/day MK-7 or placebo for 6 months and found no effect on arterial calcification measured on CT, despite a large fall in inactive matrix Gla protein. Diederichsen 2022 (Circulation), the AVADEC trial, gave 365 men aged 65 to 74 with aortic valve calcification 720 mcg/day MK-7 plus 25 mcg vitamin D or placebo for 2 years and found no significant slowing of aortic valve calcification progression. Both were 6 months to 2 years and enrolled people who already had calcification or diabetes.
The studies · 2
Zwakenberg 2019, Am J Clin Nutr · Am J Clin Nutr
Diederichsen 2022, Circulation (AVADEC) · Circulation
180 mcg of MK-7 daily improved arterial stiffness over 3 years in postmenopausal women
The same MK-7 dose that slowed bone loss also modestly improved a measure of artery stiffness over three years in postmenopausal women.
Knapen 2015 reported the vascular endpoints from the same 244-woman, 3-year MK-7 (180 mcg/day) trial. Carotid-femoral pulse wave velocity and the stiffness index beta decreased significantly versus placebo across the whole group, with the effect strongest in women whose baseline stiffness index was above the median of 10.8, alongside a 50 percent fall in inactive (dephospho-uncarboxylated) matrix Gla protein. Arterial stiffness is a surrogate marker; the trial did not measure heart attacks, strokes or cardiovascular death.
Who this may not transfer to:Measured only in postmenopausal women; the arterial-stiffness effect of MK-7 has not been tested in men or younger adults.
The study · 1
Knapen 2015, Thromb Haemost · Thromb Haemost
People eating the most K2 in food had about half the coronary heart disease deaths (observational)
People who ate more vitamin K2 in food had less heart disease death and less hardening of the aorta over the following years, though this is an association rather than a tested effect.
Geleijnse 2004 (J Nutr), the Rotterdam Study, followed 4,807 adults aged 55 and over free of myocardial infarction at baseline. The highest tertile of dietary menaquinone (K2) intake, mainly from cheese and other dairy and from meat, was associated with lower coronary heart disease mortality (relative risk about 0.43 versus the lowest tertile), lower all-cause mortality, and less severe aortic calcification. Dietary phylloquinone (K1) intake was not associated with these outcomes. As an observational cohort it cannot establish that the K2 itself produced the lower risk.
The study · 1
How it works
K2 activates osteocalcin and matrix Gla protein, the basis of the vitamin D partnership
Vitamin K2 activates the proteins that route calcium into bone and away from arteries, which is why it is proposed as the partner to vitamin D.
Vitamin K is the cofactor for gamma-glutamyl carboxylase, which carboxylates vitamin K-dependent proteins. Osteocalcin, once carboxylated, binds calcium into hydroxyapatite in bone; matrix Gla protein, once carboxylated, is a potent local inhibitor of vascular calcification. Aaseth 2024 (Nutrients) reviews this mechanism and the rationale for combining vitamins K and D: vitamin D increases intestinal calcium absorption while K2 activates the proteins that determine where calcium is deposited. Human dosing data support the biochemical step: Shiraki 2009 (J Bone Miner Metab) showed short-term menatetrenone (MK-4) increased the gamma-carboxylation of osteocalcin in postmenopausal osteoporosis. Carboxylation is a measured surrogate; whether it translates into fewer fractures or cardiovascular events is the question the clinical trials address.
The studies · 2
Aaseth 2024, Nutrients · Nutrients
Shiraki 2009, J Bone Miner Metab · J Bone Miner Metab
MK-7 is absorbed and retained far longer than MK-4 or K1
MK-7 stays in the blood much longer than MK-4 or K1, so a small daily MK-7 dose does the work a much larger MK-4 dose would.
Sato 2012 (Nutr J) compared MK-4 and MK-7 bioavailability in healthy women and found that MK-4 given at a nutritional dose was not detectable in serum, whereas MK-7 was well absorbed and raised serum concentrations, both after a single dose and after continued intake. Schurgers 2007 (Blood) showed natto-derived MK-7 has a substantially longer half-life and more stable serum levels than K1 (phylloquinone), giving better carboxylation of osteocalcin at low doses. These are pharmacokinetic differences in absorption and retention, not a demonstrated clinical superiority of one form for bone or cardiovascular outcomes.
Who this may not transfer to:The head-to-head absorption comparison was done in healthy women; pharmacokinetics are not expected to differ greatly by sex but were not tested in men here.
The studies · 2
Sato 2012, Nutr J · Nutr J
Schurgers 2007, Blood · Blood
Ways to Do It
For most people this starts with food, because the foods that carry K2 are ordinary, and it pairs with whatever you already do for vitamin D. A modest MK-7 supplement is a reasonable addition if your diet is short of fermented and animal sources, at the dose the trials used.
Natto, the fermented soybean dish, is by far the richest source of MK-7, since the bacteria that ferment it are prolific K2 makers. Aged and hard cheeses such as Gouda, Edam and Brie carry meaningful amounts, and egg yolks, chicken, and grass-fed animal fats supply MK-4. Fermented foods in general add some. If natto is not to your taste, a couple of servings of aged cheese and regular egg yolks are the everyday route.
The whole rationale for K2 is as the partner to vitamin D, so the simplest move is to keep the vitamin D habit you have (sun, oily fish, or a modest supplement) and cover K2 from food alongside it. You are not adding a project; you are filling in the other half of the calcium job, the part that puts calcium into bone and keeps it out of artery walls.
If you rarely eat natto, aged cheese or egg yolks, a generic MK-7 supplement at 90 to 180 mcg a day is the form and dose used in the bone and arterial-stiffness trials. MK-7 is fat-soluble, so take it with a meal that contains some fat. Many products combine it with vitamin D3 in one capsule, which matches how the pair is meant to work.
The 45 mg a day MK-4 used in the Japanese fracture trials is a licensed osteoporosis drug at a dose hundreds of times a nutritional amount, taken in divided doses. That is a medical decision for someone with diagnosed osteoporosis, made with a clinician, not a supplement to self-start. For general use the microgram MK-7 dose above is the one the everyday evidence sits behind.
Go Deeper
- Vitamin D: the nutrient that raises calcium absorption, the natural partner to K2, and a case study in the same gap between correcting a deficiency and an oversold routine supplement.
- Resistance training: the intervention with the strongest record for building bone, and the partner to any nutritional bone strategy.
- Omega-3 fish oil: another supplement with a strong mechanism and disappointing trials on hard outcomes, where matching dose and form to the goal is the main task.
The Chinese Medicine View
Vitamin K2 was identified in the twentieth century, so it has no entry in the classical Chinese pharmacopoeia, no channel, flavor or temperature assigned by any historical text, and this framing invents none. What the tradition can offer is a way to place the foods that carry it, held as a lens rather than as evidence.
The richest K2 foods are fermented and aged: natto, aged cheeses, and cured animal products. Chinese dietary thinking has a long and specific relationship with fermented foods, reading them as warming and as supporting the Spleen and Stomach in their work of transformation, which is why fermented and aged preparations appear across the tradition. It also reads rich, aged and fatty foods as building and moistening, useful for someone depleted and burdening for someone already damp or phlegm-laden, where more richness worsens the accumulation. The bone connection has its own resonance: the Kidney in Chinese medicine governs the bones and marrow and stores Jing, the deep reserve that thins with age, and K2's clearest role is in that same territory of mineralizing bone in the older body.
None of this maps onto menaquinones in any literal way, and reading it as if the tradition anticipated the modern finding would be a mistake. A practitioner would not hand everyone the same daily portion of a rich fermented food any more than the same herb, but would ask who is in front of them. That instinct, that the right amount depends on the person and their state, sits comfortably beside a modern picture where the benefit depends on dose, form and who you are, and it is offered here as a way of thinking rather than a claim about the vitamin.
Cautions For This Practice
Extra restraintEverything to be aware of is here, in one place. This practice suits most healthy people; a few situations call for real care.
Vitamin K2 works against warfarin and can push the INR out of range
Vitamin K antagonists (warfarin, acenocoumarol, phenprocoumon) act by inhibiting vitamin K recycling, so exogenous vitamin K directly opposes them. Violi 2016 (Medicine, Baltimore) systematically reviewed the interaction between dietary vitamin K intake and anticoagulation and concluded that everyday dietary fluctuations destabilize INR less than clinical lore holds, while noting that larger and more consistent intakes, such as supplements, are a different exposure. The clinically safe course on a vitamin K antagonist is consistency: do not start, stop or change a vitamin K supplement without the clinician who manages the INR, because a new steady dose shifts the drug's effect.Violi 2016, Medicine (Baltimore)
Warfarin and other vitamin K antagonists: do not add K2 on your own
This is the interaction that matters. Warfarin and related blood thinners (the vitamin K antagonists) work by blocking vitamin K, so any vitamin K, including a K2 supplement, is their direct counterweight and can blunt the drug and swing your INR out of range. A systematic review found that ordinary day-to-day swings in dietary vitamin K destabilize these drugs less than was long assumed, but a supplement is a higher and more consistent dose than food, and the pharmacological antagonism is not in dispute. If you take warfarin or a similar drug, do not start, stop or change a vitamin K2 supplement without the prescriber who manages your INR. Consistency is what keeps these drugs safe, and a new supplement breaks it.
K2 supplements are well tolerated, within the usual supplement caveats
At the microgram MK-7 doses sold as supplements, vitamin K2 has a good tolerability record and no established toxic upper level, which is different from vitamin D or A. That is not a reason to megadose: the trials that showed anything used 90 to 180 mcg a day, and there is no demonstrated gain from going far above that. As with any supplement, tell a clinician what you take before surgery or if you are managing a serious condition.
Pregnancy, breastfeeding, and children
The bone and cardiovascular trials were done in adults, most of them postmenopausal women or older men, so there is little trial data on K2 supplements in pregnancy, breastfeeding, or childhood. Getting K2 from food is part of a normal diet; before taking a supplement in these situations, clear it with a clinician first, since the evidence base does not cover them.
Start slow, be smart, read the research, and consult a professional if you have any concerns. This is here to inform your choice, not make it for you.
Common Questions
Do I need K2 if I take vitamin D?
The rationale is that they do two halves of one job. Vitamin D raises how much calcium you absorb, and K2 activates the proteins that route calcium into bone and away from artery walls, which is why the two are often paired and sold together. The mechanism is well described, and a modest MK-7 dose slowed bone loss in one three-year trial. Whether adding K2 to vitamin D changes fractures or heart outcomes has not been shown directly, so it is a reasonable, low-risk pairing whose necessity has not been proven. Food sources cover it for many people.
What is the difference between MK-4 and MK-7?
They are both vitamin K2 but behave differently in the body. MK-7, richest in natto and made by bacteria, is absorbed well and stays in the blood a long time, so a small daily dose of 90 to 180 mcg is enough, and it is the form in most supplements and in the bone and arterial-stiffness trials. MK-4, made in animal tissue, clears from the blood fast, so the Japanese osteoporosis studies used a very large 45 mg drug dose in divided doses. For everyday use, MK-7 is the practical form.
Which foods have the most vitamin K2?
Natto, the fermented soybean dish, is far and away the richest, because the bacteria that ferment it produce large amounts of MK-7. After that, aged and hard cheeses such as Gouda, Edam and Brie carry useful amounts, and egg yolks, chicken, liver and grass-fed animal fats supply the MK-4 form. Fermented foods generally add some. Leafy greens are rich in vitamin K1 but not K2, so the two branches come from different parts of the diet.
Does vitamin K2 protect your heart?
The food evidence is encouraging and the trial evidence is not there yet. In the Rotterdam Study, people who ate the most K2 in food had less heart disease death and less aortic calcification, but that is an association and cannot show the K2 caused it. When randomized trials tested K2 supplements against calcification of arteries and heart valves, they found no slowing over one to two years. One trial did improve arterial stiffness, a surrogate measure, over three years. So the mechanism is established and the food association is consistent, while a demonstrated reduction in heart attacks or strokes has not been shown.
Explore Related
Other pages this one connects to, by the evidence they share, the outcomes they touch, and the ground they cover.
All 13 sources on this page independently checked and cross-referenced.
Thomas Dehli, Founder & Editor, Sacred Lotus
Sacred Lotus has published Chinese medicine reference material since 2001. Integrative pages are held to the same standard as the herb and formula library: cite the source, grade the claim at its real strength, and say where the research has not looked. This page is educational and it is not medical advice. Last reviewed and updated August 9, 2026.
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