Can vitamin K2 (MK-7) improve bone strength without raising bone density?
In the evidence this review assembles, yes. MK-7 at 180 µg/day for 3 years slowed bone loss and helped maintain bone strength in healthy postmenopausal women, and in rats 5 months of MK-7 significantly improved bone strength while bone mineral density moved only modestly. This is a narrative review, not a trial with fractures as an endpoint, so it explains a mechanism and gathers supporting studies rather than proving that MK-7 prevents broken bones.
That distinction matters most to the person who has just been handed a DEXA report. A bone density scan measures how much mineral is packed into a given area of bone. It does not measure the protein scaffold that mineral sits on, and it does not measure how much a bone can bend before it cracks. Two people with the same T-score can have different bones.
Why a bone density score misses part of the picture
Collagen occupies more than half the volume of bone, and it is what gives bone its flexibility and elasticity. Mineral makes bone hard. Collagen keeps it from being brittle. A DEXA scan reads the mineral and is blind to the scaffold.
The review’s central argument is that MK-7 works mostly on that second half. Its authors put it plainly: the primary benefit of MK-7 is maintaining and improving bone quality, and therefore bone strength, rather than increasing bone mineral density.
The clearest illustration in the paper comes from the animal data. In one 5-month rat study, MK-7 prevented bone mineral density loss only to a limited degree but significantly improved bone strength. The number that a scan would report barely moved. The property that determines whether a bone breaks did.
What the review found
- MK-7 at 90 to 180 µg/day promotes carboxylation of osteocalcin, the vitamin K-dependent protein that osteoblasts use to direct calcium into bone.
- 180 µg/day for 3 years inhibited bone loss and helped maintain bone strength in healthy postmenopausal women.
- In rats, 5 months of MK-7 significantly improved bone strength while bone mineral density changed only modestly.
- In postmenopausal women given MK-4 at 45 mg/day for 3 years, bone mineral density did not change, but bone quality indices of the femur increased. Same pattern, a different form of K2, a dose roughly 250 times larger.
- Restricting vitamin K intake to 72 µg/day, a level inside several countries’ recommended range, dropped osteocalcin carboxylation by about 40% from baseline over 4 weeks.
- Natto consumption tracks inversely with hip fracture incidence across Japanese regions, an observational pattern rather than a controlled result.
- 600 µg/day for 1 month produced no change in blood or urine biochemistry, and 3 years of supplementation produced no reported adverse effects.
How MK-7 works
MK-7 is the precursor of MK-4, and the conversion is the point. When rats were fed a nutritional dose of MK-4 directly, MK-4 levels in tissues outside the liver did not rise. When they were fed MK-7, MK-4 rose significantly in the femur, brain, and testis. The long half-life of MK-7 in serum is what lets it reach those tissues, while MK-4 taken by mouth clears too fast to get there at nutritional doses.
Once it arrives, there are two pathways. MK-4 acts as a ligand for the steroid and xenobiotic receptor, SXR/PXR, which switches on genes involved in bone formation. Separately, MK-7 supports carboxylation of osteocalcin and matrix Gla protein, and increases collagen production. Osteocalcin has to be carboxylated to bind calcium; uncarboxylated osteocalcin circulates without doing the job, which is why the ratio of the two is used as a readout of vitamin K status in bone.
The recommended intakes were set for clotting, not for bone
This is the part of the review with the widest practical reach. Current national recommendations sit at 120 µg/day for men and 90 µg/day for women in the United States, 65 and 55 µg/day under WHO and FAO guidance, and 75 µg/day in the European Commission’s figure. Japan raised its own recommendation in 2015 from 75 µg/day for men and 65 for women to 150 µg/day for both.
Those numbers were derived from what the liver needs to make clotting factors. The review’s argument is that the amount of vitamin K required to fully carboxylate osteocalcin in bone is higher than the amount required to keep blood clotting normally, and the 72 µg/day experiment is the evidence they lean on: an intake that satisfies the clotting requirement still let osteocalcin carboxylation fall by about 40%.
Dr. Kumar’s Take
I read this as a well-argued mechanism paper, and I want to be clear about what it is and is not.
Two things give it weight. The bone quality argument is real physiology, not marketing. Collagen genuinely is more than half of bone by volume, and a DEXA scan genuinely cannot see it, which is why some people fracture at a T-score that looks acceptable and others do not fracture at a T-score that looks alarming. And the same pattern shows up across species and across both forms of K2: density barely moves, strength improves.
Three things temper it. First, all three authors are employed by J-OIL MILLS, a company in the MK-7 ingredient business. They declared no conflict of interest and the paper received no external funding, but a narrative review selects which studies to include, and that selection is where an interest shows up. Second, a narrative review is not a systematic one. Nobody pre-registered the search, so I cannot tell how much contrary evidence sits outside the frame. The review itself notes one rat study where MK-7 did nothing to bone strength or density in ovariectomized animals, which is at least an honest inclusion. Third, and most important, none of this is a fracture trial. The endpoint that matters to a patient is a broken hip, and the strongest fracture evidence here is the regional natto correlation, which is observational.
So the honest version is narrower than the headline. MK-7 improves a set of measurements that plausibly relate to fracture risk, at a dose that is cheap and appears safe, on top of whatever else is being done. It is not a replacement for osteoporosis treatment, and anyone who has just been diagnosed should be having the treatment conversation with their doctor rather than substituting a supplement for it.
That said, the risk-to-benefit math here is unusually friendly. Bone loss starts well before menopause, and the 180 µg/day dose is a fraction of the 600 µg/day that produced no biochemical change over a month. So if you are past 40, or you already carry a fracture risk on paper, MK-7 is a reasonable thing to add. That is my extension of the evidence rather than the review’s, which is a mechanism paper and makes no recommendations.
How to take MK-7
Take it with a meal that contains some fat. Vitamin K is a fat-soluble vitamin, absorbed through the same route as dietary fat, so a capsule swallowed with black coffee on an empty stomach is working against itself. Whole eggs, olive oil, nuts, yogurt, or fatty fish in the same meal are all enough. That is general nutrition rather than a finding of this review, which does not test meal timing.
Two other practical points follow from the paper itself. Consistency matters more than dose, because the effect being measured is the carboxylation of osteocalcin, which reflects the level of vitamin K available day after day rather than any single serving. And MK-7 is worth choosing over MK-4 specifically, since the human MK-4 studies needed 45 mg/day, roughly 250 times the MK-7 dose, to move bone quality at all.
Frequently Asked Questions
Does vitamin K2 treat osteoporosis?
No. This review is a mechanism paper, and no trial in it used fractures as an endpoint. What it shows is that MK-7 improves markers of bone quality and measures of bone strength. That is a reason to consider it alongside osteoporosis treatment, not instead of it.
How much MK-7 was used in these studies?
The human bone studies in this review used 180 µg/day, and osteocalcin carboxylation improved in the 90 to 180 µg/day range. The 3-year postmenopausal study used 180 µg/day.
Will MK-7 raise my bone density on a DEXA scan?
That is not what the evidence shows. Across the rat and human studies collected here, bone mineral density changed little while measures of bone strength and bone quality improved. A follow-up scan is the wrong instrument for measuring what MK-7 does.
Should I take MK-7 with food?
Yes, with a meal containing some fat. Vitamin K is fat-soluble and is absorbed alongside dietary fat, so a capsule taken on an empty stomach is working against itself. Eggs, olive oil, nuts, yogurt, or fish in the same meal are enough. This is general nutrition rather than something this review tested.
What foods contain MK-7?
Natto, a fermented soybean dish, is by far the richest source, at 200 to 400 µg per 30 to 45 g serving. Some fermented cheeses contain smaller amounts.
How does MK-7 compare to MK-4?
MK-7 has a much longer half-life in serum. In rats, a nutritional dose of MK-4 did not raise MK-4 levels in tissues outside the liver, while MK-7 did, because MK-7 survives long enough to reach them and is converted there. MK-4 studies in humans have used pharmacological doses such as 45 mg/day, roughly 250 times the MK-7 dose.
Is MK-7 safe?
In the data reviewed here, 600 µg/day for 1 month produced no change in blood or urine biochemistry, no hypercoagulable state was seen at doses above the recommended intake, and 3 years of supplementation produced no reported adverse effects.
Can I take MK-7 if I am on warfarin?
No, not without your prescriber’s involvement. Vitamin K is the direct antagonist of warfarin, and the review specifically states that patients on warfarin should avoid natto. Even low doses of MK-7 can shift anticoagulation.
Related reading
3-Year Study Finds Vitamin K2 (MK-7) Helps Prevent Bone Loss in Postmenopausal Women is the randomized controlled trial behind the 180 µg/day figure quoted above, in 244 women.
Natto and Bone Loss: How Much to Eat for Vitamin K2 Benefits works out the food dose, if you would rather get MK-7 from a meal than a capsule.
Why MK-7 May Be the Better Vitamin K2 for Bone and Heart Health covers the absorption and half-life comparison in more detail.
How All Forms of Vitamin K Become MK-4 in Your Body follows the conversion step that this review treats as central.
Even Low-Dose Vitamin K2 Can Disrupt Blood Thinners is the one to read first if you take warfarin.
Vitamin K2 May Slow Osteoarthritis by Protecting Cartilage and Preventing Cell Death looks at the joint side rather than the bone side.
Conclusion
The useful idea in this review is that bone strength and bone density are not the same measurement, and that a scan reports only one of them. MK-7 acts mainly on the other one, through osteocalcin carboxylation and collagen, at doses well below anything that raised a safety signal. The evidence is mechanistic and the authors have a commercial interest in the ingredient, so treat it as a reason to ask a question rather than an answer on its own.
Read the full study here
Sato T, Inaba N, Yamashita T. MK-7 and Its Effects on Bone Quality and Strength. Nutrients. 2020;12(4):965.
