Vitamin K2 keeps calcium out of your arteries

Vitamin K2 has a real biological role in how artery walls handle calcium, and two trials published in 2026 report that it slowed calcium buildup in the coronary arteries of people whose arteries were already calcified. One tested K2 on its own. The other, which was larger, gave K2 together with vitamin D, so it cannot show which of the two did the work. Across the wider set of trials the picture is mixed, and no trial has shown that K2 prevents buildup, removes it, or lowers the rate of heart attacks or strokes.

Both positive trials measured calcium scores rather than heart events, and scores still rose in every group. They used 360 and 720 micrograms a day of menaquinone-7, the form of K2 used in most supplements. An earlier trial of the 720 microgram combination found no significant slowing of coronary calcium overall. A trial in people with type 2 diabetes found no effect on calcification. The only long trial in healthy people measured artery stiffness, not calcium. A three-year trial of 450 people from the general population, with coronary calcium as its main outcome, is due to finish in early 2027.

The clearest test of K2 on its own is a 2026 trial in the Netherlands of 180 people with symptoms of coronary artery disease and moderate existing calcification, meaning calcium scores between 50 and 400. It was randomized, blinded and placebo controlled, registered before enrolment began, and it reported on the outcome it declared in advance. Over two years the median calcium score rose from 145 to 214 on placebo and from 135 to 184 on menaquinone-7, a difference the authors report as statistically significant after adjustment. Calcium mass followed the same pattern. The authors describe the effect as slower calcification of plaques that were not yet calcified, and state that what this means for plaque stability remains to be determined. The trial's published protocol states that its tablets were supplied free of charge by a menaquinone-7 manufacturer, alongside a grant from the Netherlands Heart Foundation.

The largest trial, also published in 2026, was run in Denmark and tested K2 together with vitamin D. It enrolled 398 people with severe coronary calcification, meaning calcium scores of 400 or more, and gave them 720 micrograms of menaquinone-7 plus 25 micrograms of vitamin D3 a day, or placebo, for two years. It was randomized, double blind and registered before enrolment began. Calcium scores rose by an average of 196 units on the supplement and 248 on placebo, a difference of 52 units with a confidence interval from 24 to 79, and the result was similar in women and men and at higher and lower starting scores. The same research group had earlier tested the same combination in older men with calcified aortic valves. Among the 304 of those men who had no known coronary heart disease, coronary calcium rose by 203 units on the supplement and 254 on placebo, which was not a significant difference; the rise was slower only among men who started with scores of 400 or more, the same threshold the later trial used for enrolment. In both trials the study tablets were provided by two companies, one of which manufactures menaquinone-7. Because the placebo contained neither vitamin, these trials cannot separate what K2 did from what vitamin D did.

The other trial of K2 on its own with calcification as its outcome points the other way. In 68 people with type 2 diabetes and cardiovascular disease, six months of menaquinone-7 at 360 micrograms a day made no difference to calcification on a standard CT scan. On a newer PET scan that tracks active calcification, the supplemented group tended toward more activity than placebo, a result that did not reach statistical significance and whose meaning the authors say is not yet established. The two syntheses read differently. A 2023 meta-analysis of 14 trials and 1,533 people reported that vitamin K slowed the rise in coronary calcium scores by about 17 units, with a confidence interval running from about 34 units to just under 1. It combined vitamin K1 and K2 trials without reporting them separately, so it does not isolate K2, and it included trials in people on dialysis. A 2023 systematic review limited to people without kidney disease summarised its five vitamin K trials as showing no slowing of calcification, although its own table records one vitamin K1 trial that did slow calcification of the aortic valve. Only one of those five tested K2 on its own. Both were completed before the two 2026 trials were published.

The only long trial in generally healthy people gave 180 micrograms of menaquinone-7 a day to postmenopausal women for three years. Against placebo, measures of arterial stiffness improved in the group as a whole, and more of them improved in women whose arteries were stiffer at the start. It did not measure calcium. Stiffness was a secondary outcome of that trial, whose main outcome was bone strength. In 2020 the European Food Safety Authority assessed it, together with a one-year trial of the same product and an uncontrolled study, all submitted by the manufacturer, and concluded that no conclusions could be drawn from any of the three. For the three-year trial it cited 14 vascular measures tested without correction for multiple testing and an analysis that did not account for repeated visits. It found that a cause and effect relationship between the product and keeping the arteries elastic had not been established. Stiffness and calcification are related, but a change in one is not a finding about the other. In rats given warfarin to block vitamin K, arteries calcified quickly, and switching the animals to a diet high in vitamin K1 or K2 cut arterial calcium by about half. That shows the pathway can work in an animal model with drug-induced calcification. Whether the same happens with the slow, age-related calcification in human arteries is the question the human trials have not settled. The NIH Office of Dietary Supplements describes the role of the different forms of vitamin K in arterial calcification as unclear and still under active research.

On safety, vitamin K counteracts warfarin and similar anticoagulants, and people taking them are advised to keep their vitamin K intake consistent. For anyone on one of those medicines, adding K2 is a conversation with whoever prescribes it, not a shelf decision.