Vitamin K2 and D3 supplements slowed coronary calcium buildup in a 398-person trial

Vitamin K2 has a reputation in supplement marketing as a nutrient that steers calcium into bones and keeps it out of arteries. The idea rests on real biology, but it has been tested in people far less than it has been promoted.

A trial in the journal Circulation put it to a test in 398 people whose heart arteries were already heavily calcified. Over two years, calcium scores rose more slowly in those taking vitamin K2 with vitamin D3 than in those taking a placebo. Whether that translates into fewer heart attacks, the trial could not say.

What vitamin K does and what calcium scores measure

MedlinePlus notes that vitamin K is known as the clotting vitamin, because the liver needs it to make proteins that let blood clot. Some studies suggest that vitamin K helps maintain strong bones in older adults. The form in supplements marketed for arteries is usually K2.

Calcium in the heart’s arteries is measured with a quick CT scan. RadiologyInfo explains that the amount of calcification, expressed as the calcium score, helps predict the likelihood of a heart attack. Scores over 400 indicate extensive plaque. For a fuller guide, see our explainer on what coronary calcium scores mean.

How the DANCODE vitamin K2 trial worked

The trial enrolled people at several centers who had a calcium score of 400 or more, meaning severe calcification. They were randomly assigned to daily vitamin K2 (720 μg/d) plus vitamin D3 (25 μg/d) or placebo for 24 months. The K2 dose is several times what is normally found in the diet.

Neither participants nor researchers knew who got what. Everyone had calcium scans at the start, after one year and after two years. A subset also had CT angiography, a scan that uses dye to show the whole plaque, including the soft parts that do not contain calcium.

What happened to calcium scores

Calcium scores rose in both groups, as they usually do in people with advanced plaque. The mean increase was 196 AU with vitamin K2 and D3 and 248 AU with placebo, where AU stands for Agatston units, the standard scale for calcium scores. That is a gap of about 52 units, or roughly a fifth less growth with the supplements. The effect was similar in men and women and at different starting scores.

The angiography subset added an important detail. Total plaque volume grew about the same in both groups, and the soft plaque did not change differently either. Only the calcified part of the plaque grew more slowly with the supplements, by about 8 cubic millimeters.

Why a slower-rising calcium score is hard to interpret

Calcium scores predict heart risk well, but they are not the same as risk. Calcium is part of how plaque matures and stabilizes, and some treatments that clearly lower heart attacks, such as statins, can increase the calcium in plaque. So slower calcium buildup could be good, neutral, or in theory a sign of plaque staying softer, and the trial was not designed to tell.

The authors note that the reduction in calcification progression was not associated with an increase in noncalcified plaque volume, which argues against the worrying version. But the only way to know whether the supplements help is to measure heart attacks, strokes and deaths, which this trial did not.

Where the vitamin K2 findings fit

The vitamin D half of the combination has been tested for heart outcomes directly. In the VITAL trial of 25,871 adults, supplementation with vitamin D was not associated with a lower risk of either of the primary end points, which included major cardiovascular events. That makes it less likely that vitamin D alone explains the result, but the trial design cannot separate the two vitamins.

Before DANCODE, vitamin K2 had mostly been studied in small trials with mixed results on artery and valve calcification. The closest comparison is a Dutch trial published in JAMA Cardiology in 2026, which gave 180 patients with symptomatic coronary artery disease either vitamin K2 alone, in the form called menaquinone-7 (MK-7), or a placebo for two years. Its authors concluded that supplementation with MK-7 for 2 years may slow calcification in noncalcified plaques, meaning plaque that had not yet hardened with calcium, and said the clinical meaning of that finding is still to be determined. We covered that trial in a separate article.

DANCODE is larger and longer than most vitamin K2 trials, and it added vitamin D. That is why it matters, and why its outcome, a scan measure rather than clinical events, is the main limit.

What the DANCODE vitamin trial cannot tell us

The trial ran for two years in people with severe calcification, mostly older men. It cannot say whether the supplements help people with lower scores, whether effects continue beyond two years, or whether they change the chance of a heart attack or stroke.

It also cannot separate K2 from D3, and the dose tested is higher than a typical diet provides. Vitamin K has a known interaction: MedlinePlus notes that vitamin K or foods containing vitamin K can affect how warfarin works, a common blood thinner.

What this changes for vitamin K2 and heart health

The trial is a signal worth following up, not a reason to change care. It shows that the combination can slow one measure of artery disease, and it provides the groundwork for a larger trial that counts heart attacks and strokes.

Current heart guidance does not include vitamin K2. The treatments with proven effects on heart attacks in people with heavily calcified arteries remain those for cholesterol, blood pressure and other risk factors, managed by a doctor who knows the person’s history.