The short version
- In the Rotterdam Study of 4,807 people, the highest tertile of dietary menaquinone intake was associated with a relative risk of 0.43 for coronary heart disease mortality and 0.48 for severe aortic calcification versus the lowest tertile.
- Three years of 180 micrograms of MK-7 daily in 244 healthy postmenopausal women decreased the age-related decline in bone mineral density at the lumbar spine and femoral neck, but not at the total hip.
- The same three-year trial found carotid-femoral pulse wave velocity significantly reduced, with the largest improvements in women whose baseline arterial stiffness was above the median.
- The AVADEC trial randomised 365 men to 720 micrograms of MK-7 plus 25 micrograms of vitamin D for 24 months and found no effect on aortic valve calcification progression, with a mean difference of 17 arbitrary units (P = 0.64).
- In that same trial the vitamin K biomarker moved strongly, with dephosphorylated uncarboxylated matrix Gla protein falling 212 pmol/L versus a 45 pmol/L rise on placebo, while the clinical outcome did not change.
The pitch for pairing vitamin K2 with D3 is one of the most persuasive stories in the supplement aisle, and it is persuasive because the mechanism genuinely makes sense. Vitamin D increases calcium absorption. Vitamin K activates matrix Gla protein, which inhibits calcium deposition in arterial walls. Therefore, the argument goes, K2 directs calcium to bone and away from arteries, and taking D without it is careless.
Everything up to "therefore" is real biology. The word doing the work is "therefore".
Where the story came from
The Rotterdam Study followed 4,807 people with dietary data and no history of myocardial infarction from 1990 to 2000. Comparing the highest tertile of dietary menaquinone intake to the lowest, the relative risk of coronary heart disease mortality was 0.43 (95% CI 0.24 to 0.77). All-cause mortality was 0.74 (0.59 to 0.92) and severe aortic calcification 0.48 (0.32 to 0.71). Phylloquinone, the K1 form found in green vegetables, was not related to any outcome.
That is a striking finding and it launched a category. It is also observational and dietary, which means the people eating the most menaquinone — largely from fermented foods and certain cheeses in that Dutch cohort — differed from those eating the least in ways no adjustment fully captures.
The supplement trials, in order
Two three-year randomised trials in the same population of healthy postmenopausal women (244 participants, 180 micrograms of MK-7 daily) form the positive evidence.
The bone trial found that MK-7 significantly improved vitamin K status and decreased the age-related decline in bone mineral content and density at the lumbar spine and femoral neck, though not at the total hip. Bone strength indices were also favourably affected.
The vascular trial, in the same cohort, found carotid-femoral pulse wave velocity and the Stiffness Index beta significantly decreased over three years, with the clearest improvements in women whose baseline stiffness was above the median. MK-7 reduced dephosphorylated uncarboxylated matrix Gla protein by 50% versus placebo, confirming the mechanism was engaged.
So: two positive three-year trials, a plausible mechanism, and a biomarker that moves exactly as predicted. This is a good-looking hypothesis.
And then the trial that tested it on a hard endpoint
The AVADEC trial randomised 365 community-dwelling men with an aortic valve calcification score above 300 arbitrary units to 720 micrograms of MK-7 plus 25 micrograms of vitamin D daily, or matching placebo, for 24 months. Mean age was 71.
Aortic valve calcification score increased by 275 units on treatment and 292 on placebo. The mean difference was 17 units (95% CI -86 to 53, P = 0.64). No significant difference in aortic valve area, peak aortic jet velocity, heart valve surgery, all-cause death or cardiovascular events. Progression of aortic and coronary artery calcification was not significantly different either.
The one thing that did move was the biomarker: dephosphorylated uncarboxylated matrix Gla protein fell by 212 pmol/L on treatment versus a rise of 45 on placebo (P < 0.001). The intervention did precisely what the mechanism says it should do to the protein. It did not change the calcification.
That gap — biomarker moves, outcome does not — is one of the most common ways a supplement hypothesis fails, and it is worth recognising the pattern when you see it.
What this means for the bottle in your hand
It means K2 is unproven rather than disproven, which is a genuinely different thing. The bone data in postmenopausal women is the most encouraging part of the file, and 180 micrograms of MK-7 over three years is not a fringe protocol. If you are taking K2 for that reason, you are not being unreasonable.
What is not supported is the framing that K2 is a required safety component for vitamin D, or that it neutralises the concerns around calcium supplements. AVADEC tested K2 and D together in men who already had substantial calcification, which is the exact population where the mechanism should have shown up most clearly, and found nothing on the outcome. Anyone using K2 as permission to push a vitamin D dose higher should reconsider both halves of that plan — the evidence on how much vitamin D to take does not support going up, with or without K2.
One safety note that is not optional. Vitamin K antagonises warfarin. If you take warfarin, a menaquinone supplement is a change in your anticoagulation, not a wellness addition, and it belongs on the list of supplements that interact with medication that your clinic must know about before you start or stop it.
What we'd actually tell you
If you eat natto, fermented foods or aged cheese, you are getting menaquinone already. If you want to take MK-7 for bone density after menopause, the trial dose is 180 micrograms a day and the timescale is years, not weeks — go in with that expectation.
If you are taking it because a vitamin D product told you that you had to, you are buying insurance against a risk that the best trial did not find.
Good questions
Do I need to take K2 with vitamin D?
No trial has shown that you do. The mechanism is real, but the largest randomised test of K2 plus vitamin D, in 365 men with existing aortic valve calcification, found no effect on calcification progression over two years even though the vitamin K biomarker responded strongly. If a vitamin D product told you K2 was required, that is a marketing claim rather than a finding.
Does vitamin K2 help bone density?
The most encouraging evidence in the file says it may, modestly, in postmenopausal women. Three years of 180 micrograms of MK-7 daily reduced the age-related decline in bone mineral density at the lumbar spine and femoral neck, though not at the total hip. That is one trial of 244 women over three years, so treat it as promising rather than settled.
What is the difference between K1 and K2?
K1, or phylloquinone, comes mainly from green leafy vegetables. K2, or menaquinone, comes from fermented foods, certain cheeses and bacterial synthesis, and MK-7 is the long-chain form with the longest half-life. In the Rotterdam cohort only menaquinone intake tracked with outcomes; phylloquinone showed no relationship with any of them.
Can I take K2 if I'm on a blood thinner?
Not without your clinic knowing. Vitamin K directly antagonises warfarin, so starting or stopping a menaquinone supplement changes your anticoagulation. This is not a reason to avoid vitamin K entirely, since steady intake is associated with more stable INR readings, but the change itself must be managed by whoever monitors your dosing.
Should I take K2 to protect my arteries if I take calcium?
There is no outcome evidence supporting that use. The trial designed to test exactly this idea, in men who already had substantial arterial and valve calcification, found no difference in progression. Using K2 as a permission slip for a calcium supplement you were not sure about is treating an unproven fix as a solved problem.
How much MK-7 was used in the trials?
The bone and arterial stiffness trials in postmenopausal women both used 180 micrograms of MK-7 daily for three years. The null cardiovascular trial used a much larger 720 micrograms daily with vitamin D for two years. Higher did not produce a better result, which is worth knowing before you buy the biggest number on the shelf.
Sources
- Geleijnse JM, Vermeer C, Grobbee DE, et al. Dietary intake of menaquinone is associated with a reduced risk of coronary heart disease: the Rotterdam Study. J Nutr, 2004. View study
- Knapen MH, Drummen NE, Smit E, Vermeer C, Theuwissen E. Three-year low-dose menaquinone-7 supplementation helps decrease bone loss in healthy postmenopausal women. Osteoporos Int, 2013. View study
- Knapen MH, Braam LA, Drummen NE, Bekers O, Hoeks AP, Vermeer C. Menaquinone-7 supplementation improves arterial stiffness in healthy postmenopausal women. A double-blind randomised clinical trial. Thromb Haemost, 2015. View study
- Diederichsen ACP, Lindholt JS, Möller S, et al. Vitamin K2 and D in Patients With Aortic Valve Calcification: A Randomized Double-Blinded Clinical Trial. Circulation, 2022. View study
These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.
