Vitamin K2, a distinct nutrient from the K1 in leafy greens, is emerging as one of the most overlooked players in heart and bone health. In the Rotterdam Study, an observational study of 4,807 Dutch adults published in the Journal of Nutrition in 2004, participants with the highest dietary intake of K2 had a relative risk of dying from coronary heart disease of 0.43, roughly a 57 percent lower risk than those in the lowest tertile.
The same group also showed significantly less severe calcification of the aorta. K1 intake showed no such association, a pattern that helped put K2 on the cardiovascular map.
How one vitamin talks to two tissues
K2 works by switching on a small family of vitamin K-dependent proteins. Two of them do most of the heavy lifting: osteocalcin, which binds calcium into the bone matrix, and matrix Gla protein (MGP), which sits in the walls of blood vessels and blocks calcium from settling there.
A 2021 review in the International Journal of Environmental Research and Public Health describes vitamin K2 as a cofactor for the gamma-carboxylation step that turns inactive MGP into its active form in vascular smooth muscle cells. Without enough K2, more MGP stays inactive, and higher blood levels of this inactive form (dp-ucMGP) track with stiffer, more calcified arteries.
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That biology is why researchers describe K2 as a kind of traffic controller for calcium, nudging it toward the skeleton and away from soft tissue.
What the trials actually show
The strongest human trial data comes from postmenopausal women, a group at high risk for both osteoporosis and arterial stiffening. In a three-year randomized, placebo-controlled trial published in Thrombosis and Haemostasis in 2015, 244 healthy postmenopausal women took either 180 micrograms of MK-7 (a long-chain form of K2) daily or a placebo.
After three years, the MK-7 group showed significant reductions in carotid-femoral pulse wave velocity, a standard measure of arterial stiffness, while the placebo group did not. Inactive MGP fell by about 50 percent compared with placebo, consistent with the proposed mechanism.
The findings are promising but limited. The trial ran in healthy women, not people with established heart disease, and larger outcome trials on heart attacks and strokes are still needed before K2 can be called a proven cardiovascular treatment.
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Where to find K2 on your plate
Most people get very little K2 from a typical Western diet. The richest natural source by far is natto, a fermented soybean dish popular in Japan, with roughly 850 to 1,100 micrograms of MK-7 per 100 grams.
Aged hard cheeses such as Gouda and Edam supply around 75 micrograms per 100 grams, and softer aged cheeses like Brie contribute a smaller amount. Egg yolks, chicken liver, and certain fatty meats add mostly the shorter-chain MK-4 form.
Supplements typically use MK-7, which stays in circulation longer than MK-4 and is the form tested in the Knapen trial. K2 is fat-soluble, so eating these foods, or taking a supplement, alongside some dietary fat improves absorption.
People on blood thinners such as warfarin should talk to their doctor before adding a K2 supplement, since any form of vitamin K can interact with these medications.
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