Vitamin K2
A fat-soluble vitamin from fermented and animal foods, best known for bone density.
- Bone density
- Heart and arteries
- Topping up vitamin K
- Blood sugar and weight
A plain-English overview, not advice. Written from published reviews and trials and from what people say in public forums.
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On this page
What is vitamin K2?
Vitamin K2 is one of the two families of vitamin K, known chemically as menaquinone. K1, the other family, comes from green leafy vegetables and algae; K2 turns up instead in fermented foods and in some foods of animal origin, and it is what supplements are usually built around, because it lasts longer in the body and reaches tissues beyond the liver. Capsules sell it as one of two menaquinones: MK-7, typically 90 to 200 micrograms, and the shorter MK-4, dosed in milligrams. Interest has grown out of one idea — that vitamin K has a hand in where calcium in the body ends up — and some reviewers now argue it deserves a daily intake figure of its own, separate from K1.
Why do people take vitamin K2?
Bone density
The thinking. Bones are where most people start with K2, and mostly they are women at or past the menopause, taking it alongside calcium and vitamin D. The thinking runs through osteocalcin, a protein made in bone that can only bind calcium into the mineral once vitamin K has switched it on.
What research has found. Two reviews of randomised trials in postmenopausal women, covering 6,853 and 6,425 people, both found spine density higher on K2 and less osteocalcin left unswitched. The trials themselves are less uniform: three years at 180 micrograms a day slowed the age-related fall in density and bone strength, while a year at 375 micrograms moved no density reading, only the fine structure of bone at the shin. This is one of the best-studied uses, and several reviews of trials broadly agree.
Heart and arteries
The thinking. The arteries are the other big reason, and they run on the same chemistry. Matrix Gla protein sits in the vessel wall and holds calcium out of it, and vitamin K is what switches it on; the unswitched form runs high where vessels are calcifying. Reviewers call the pattern the calcium paradox: too little calcium in bone, too much in the vessel wall.
What research has found. Three randomised trials looked at the arteries themselves. In two — adults on dialysis, and adults with type 2 diabetes and heart disease — calcium scores rose much the same with or without K2, though the unswitched protein fell sharply in both. The third, three years at 180 micrograms a day in 244 healthy postmenopausal women, found a fall in aortic stiffness. A fair body of trials has looked at this, and most point the same way.
Topping up vitamin K
The thinking. Some people take K2 not for one outcome but to keep the vitamin itself topped up. Even in healthy adults, whose clotting proteins are fully switched on, ten to forty per cent of the osteocalcin and matrix Gla protein in circulation is not switched on, and that gap is what a supplement is aimed at.
What research has found. Five randomised trials measured those markers. In healthy adults aged eighteen to sixty-five, daily MK-7 at doses around the recommended intake and above switched on more of both proteins, dose by dose, and two trials in adults on dialysis found the same. One compared the forms: MK-7 stayed measurable in the blood for two days after a dose, while MK-4 at food-level amounts never appeared. Research here is still young: a few studies so far, mostly pointing the same way.
Blood sugar and weight
The thinking. A smaller group takes K2 with an eye on blood sugar and weight; of the reasons here, it is the newest. It goes back to osteocalcin: once switched on, several researchers have linked it to how the body handles glucose and fat, and one review sets out a case for K2 acting on insulin sensitivity through that protein.
What research has found. A review of six MK-7 trials found lower averages for three-month blood sugar, for insulin and for insulin resistance, but nothing meaningful on body measurements or most blood fats. A three-year trial in 214 postmenopausal women found no change in body composition overall, and a shift in abdominal fat only among the women whose blood markers responded most. Studies here point in different directions, so this one is still being worked out; the dose, how long people took it and who took part all seem to matter.
What does vitamin K2 do in the body?
Vitamin K does not act on tissue directly. It is the cofactor for one chemical step, carboxylation, that switches on a small family of proteins so they can grip calcium. Two of them matter outside the liver: osteocalcin, made in bone, and matrix Gla protein, made in the vessel wall. Left unswitched, they circulate doing very little, which is why blood tests for vitamin K count the unswitched ones.
Inside the liver the same step switches on the clotting factors, and there it is essentially always complete; the proteins outside the liver are the ones left half-done on an ordinary diet. That is the argument for K2 in particular. The long-chain menaquinone is absorbed more readily than K1 and has a much longer half-life, so it stays in circulation long enough to reach those tissues. Beyond calcium, reviewers also describe K2 acting on the signals that govern how bone is broken down and rebuilt.
What do people say about taking vitamin K2?
These are anecdotes people have shared, not evidence.
What people like
- Far the commonest reason for staying on it is the idea of steering calcium into bone rather than artery walls, usually alongside vitamin D.
- A good number report no trouble at all on MK-4, some after three or four years, and a few mention teeth looking cleaner.
- People who switched form after a bad reaction very often say the trouble simply stopped, and that is why they carried on.
- A few describe no further fractures, or a bone scan holding steady over several years, while saying they cannot prove the capsule did it.
Common complaints
- A pounding or racing heart is far and away the commonest complaint, almost always on MK-7, and it fills whole threads on bone forums.
- Sleeplessness, anxiety, a wound-up feeling and higher blood pressure come next, and often appear several days in rather than straight away.
- Several describe fogginess, tingling feet or flat energy, and a good number cannot tell whether the capsule or something else is behind it.
- Cost and availability come up repeatedly, especially for MK-4, which several posters say they had to order from abroad.
How people take it
- Most take one capsule a day of MK-7 at 45 to 200 micrograms; a smaller group take MK-4 instead, dosed in milligrams.
- Taking it with vitamin D, and often magnesium and calcium, is the standard pattern; combined drops and sprays are usual in UK posts.
- People who react badly very commonly halve the dose or drop to 45 micrograms before giving up on it altogether.
- Because MK-4 clears quickly, those on it often split the day’s amount over two or three meals rather than take it once.
- Almost everyone takes it with food or in something fatty, on the grounds that it is a fat-soluble vitamin.
Read from these public discussions:
- Vit K2-7 Heart Arrhythmias and Palpitations (Inspire bone health community, 2011)
- Vitamin K2 as MK-7 (90 mcg) My Experience (Inspire bone health community, 2012)
- Why does Vitamin K2 make feel awful? (Inspire bone health community, 2014)
- Side effects and dosage of Vitamin K2 (Inspire bone health community, 2017)
- Vitamin D3 and K2? Together or not? (Mumsnet, 2021)
- VITAMIN K2 (MK7) (Inspire bone health community, 2021)
What forms of vitamin K2 are there?
| Form | What’s different | Per serving, on products we list |
|---|---|---|
| MK-7 | The long-chain menaquinone: readily absorbed, and it lasts long enough in the blood for one daily capsule. | 90 µg to 200 µg |
| MK-4 | The short-chain menaquinone, the same vitamin on a shorter tail, dosed in milligrams rather than micrograms. | not in our price tables yet |
What else is worth knowing about vitamin K2?
- Labels give the amount per serving, and a serving may be more than one capsule; MK-7 is measured in micrograms and MK-4 in milligrams, so the two look nothing alike.
- The bone reviews found no serious adverse events on K2, though one counted more minor reactions in the K2 groups; in one dialysis trial people dropped out over the smell of the tablets.
- Almost all the bone trials were in postmenopausal women, and the authors of one note that whether the same holds for men or for children has not been tested.
- Vitamin K’s oldest job is blood clotting. One trial in healthy adults checked it directly and found no change in a laboratory measure of clotting at MK-7 doses up to 360 micrograms a day.
If you take medication, are pregnant, or have a health condition, check with a pharmacist or GP first.
The research behind this page (20 studies)
- Efficacy and safety of vitamin K2 for postmenopausal women with osteoporosis at a long-term follow-up: meta-analysis and systematic review. (2022, meta-analysis)
- Efficacy of vitamin K2 in the prevention and treatment of postmenopausal osteoporosis: A systematic review and meta-analysis of randomized controlled trials. (2022, meta-analysis)
- Vitamin K2 (menaquinone-7) prevents age-related deterioration of trabecular bone microarchitecture at the tibia in postmenopausal women. (2016, randomised trial)
- Three-year low-dose menaquinone-7 supplementation helps decrease bone loss in healthy postmenopausal women. (2013, randomised trial)
- The effect of menaquinone-7 supplementation on vascular calcification in patients with diabetes: a randomized, double-blind, placebo-controlled trial. (2019, randomised trial)
- The effect of vitamin K2 supplementation on vascular calcification in haemodialysis patients: a 1-year follow-up randomized trial. (2019, randomised trial)
- Menaquinone-7 supplementation improves arterial stiffness in healthy postmenopausal women. A double-blind randomised clinical trial. (2015, randomised trial)
- Vitamin K2 supplementation in haemodialysis patients: a randomized dose-finding study. (2014, randomised trial)
- Effect of vitamin K2 supplementation on functional vitamin K deficiency in hemodialysis patients: a randomized trial. (2012, randomised trial)
- Low-dose menaquinone-7 supplementation improved extra-hepatic vitamin K status, but had no effect on thrombin generation in healthy subjects. (2012, randomised trial)
- The effect of menaquinone-7 supplementation on circulating species of matrix Gla protein. (2012, randomised trial)
- Comparison of menaquinone-4 and menaquinone-7 bioavailability in healthy women. (2012, randomised trial)
- Effect of Menaquinone-7 (MK-7) Supplementation on Anthropometric Measurements, Glycemic Indices, and Lipid Profiles: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. (2025, meta-analysis)
- Vitamin K-induced effects on body fat and weight: results from a 3-year vitamin K2 intervention study. (2018, randomised trial)
- Calcium, vitamin D, vitamin K2, and magnesium supplementation and skeletal health. (2020, review)
- Molecular Pathways and Roles for Vitamin K2-7 as a Health-Beneficial Nutraceutical: Challenges and Opportunities. (2022, review)
- The Dual Role of Vitamin K2 in "Bone-Vascular Crosstalk": Opposite Effects on Bone Loss and Vascular Calcification. (2021, review)
- Effect of vitamin K2 on type 2 diabetes mellitus: A review. (2018, review)
- Vitamin K2 in Health and Disease: A Clinical Perspective. (2024, review)
- Vitamin K 2 -a neglected player in cardiovascular health: a narrative review. (2021, review)
How much does vitamin K2 cost?
That depends on the form and the pack, so we work out the price of the same dose of every vitamin K2 product we can find and rank them.