Vitamin K2: The forgotten vitamin that protects your bones and heart

If you think of vitamin K, you probably think of blood clotting. And yes, vitamin K plays an important role in that. But there is much more to it. Vitamin K is not a single substance, but a family of related compounds, and one of them deserves special attention: vitamin K2. This vitamin is one of the most underestimated nutrients overall, and at the same time one of the most important for long-term health.

What is vitamin K2 and why is it not the same as K1?

Vitamin K1 (phylloquinone) is found in green leafy vegetables such as spinach, kale, and broccoli. It is mainly used in the liver and plays the well-known role in blood clotting.

Vitamin K2 (menaquinone), on the other hand, has a completely different function and a completely different origin. It is found in animal products and fermented foods and is used in very different tissues: mainly in bones, blood vessels, and soft tissue. The two best-known forms are MK-4 (predominantly found in animal products) and MK-7 (predominantly found in fermented soy, the so-called natto).

The key difference: vitamin K2 activates proteins that direct calcium to where it belongs and keep it away from where it does not belong.

The two most important proteins activated by vitamin K2

To truly understand the effects of vitamin K2, you need to know two proteins.

The first is osteocalcin. It is produced by osteoblasts (bone-forming cells) and is responsible for incorporating calcium into the bone matrix. Without sufficient vitamin K2, osteocalcin remains inactive, and calcium cannot properly build bone—even if enough of it is present in the blood.

The second is matrix Gla protein (MGP). It is the most powerful known inhibitor of vascular calcification. When MGP is activated by vitamin K2, it prevents calcium from being deposited in the arterial walls. Insufficient K2 intake leaves MGP inactive, and calcium can accumulate in the blood vessels, with potentially serious consequences for the cardiovascular system.

Vitamin K2 and bone health

Numerous studies show a direct connection between vitamin K2 and bone and joint health. In a controlled study published in the journal Osteoporosis International, supplementation with MK-7 significantly improved bone density in postmenopausal women. This is particularly relevant, as the decline in estrogen during this life stage makes bones especially vulnerable.

Vitamin K2 works hand in hand with vitamin D3 and calcium. While vitamin D3 promotes calcium absorption from the intestine, K2 ensures that this calcium actually reaches the bones and does not end up in the blood or soft tissue. Those who supplement vitamin D3 and calcium without taking K2 may unintentionally promote arterial calcification, because the absorbed calcium is not properly directed.

Vitamin K2 and the cardiovascular system

The so-called Rotterdam Study, a large Dutch observational study, followed over 4,800 participants over a period of 10 years. The results were clear: people with the highest intake of vitamin K2 had a significantly lower risk of heart disease and aortic calcification than those with the lowest intake. Interestingly, this effect did not apply to vitamin K1.

Further research confirms that adequate K2 intake reduces the risk of atherosclerosis. Inactive MGP is one of the best markers of calcium deposition in blood vessels, and vitamin K2 is the only known nutrient that directly activates MGP.

Where is vitamin K2 found?

This is where the real problem lies: vitamin K2 is almost absent in the modern Western diet. The richest sources are:

Animal organs, especially beef liver and beef kidney, are among the most concentrated natural sources of K2 in the form of MK-4. This is because grazing animals absorb K1 from grass and convert it into MK-4 in their bodies. Grass-fed animals have significantly higher K2 levels than conventionally raised ones.

Other notable sources include egg yolks from free-range hens, fatty cheese (especially from raw milk), butter from grass-fed animals, and natto (fermented soybeans), which has by far the highest MK-7 concentration.

For most people who do not regularly consume organ meats or natto, achieving adequate K2 intake through a normal diet alone is difficult.

Who is particularly at risk?

People who eat little or no animal products risk insufficient K2 intake. The same applies to older adults, as the conversion of K1 to K2 in the body decreases with age. Those who regularly take antibiotics may also be affected, as these disrupt the gut microbiome, which also contributes a small amount to K2 production.

In addition, low-fat diets can impair K2 absorption. As a fat-soluble vitamin, K2 requires dietary fat to be absorbed in the intestine.

Vitamin K2 and animal-based organ supplements

Freeze-dried beef organs, especially liver, are a natural and bioavailable source of MK-4. Since the MK-4 form is directly stored in animal tissues, people who regularly consume beef organs or high-quality organ supplements benefit from this nutrient form in the way nature intended. Not a synthetic isolate, but a nutrient embedded in the full nutritional context of the food, along with hundreds of other cofactors.

The interaction with other nutrients

Vitamin K2 does not work alone. It is part of a fascinating network of fat-soluble vitamins:

Vitamin D3 increases calcium absorption in the intestine and stimulates the production of osteocalcin and MGP. Vitamin K2 then activates these proteins. Together, they are far more effective than any single vitamin alone.

Vitamin A also supports the production of vitamin K–dependent proteins and works synergistically with D3 and K2. Organ meats provide all three vitamins simultaneously, which is another advantage of whole food sources compared to synthetic isolated supplements.

Conclusion: A small vitamin with a big impact

Vitamin K2 is one of those nutrients whose importance was long underestimated because it was confused with K1. However, research over the past two decades has painted a clear picture: K2 is essential for bones, heart, and blood vessels, and most people do not get enough of it.

The good news is that nature already solved this problem long before dietary supplements existed. Grazing animals store MK-4 in their organs, especially in the liver. Those who regularly include these foods in their diet—whether by cooking with organ meats or using high-quality organ supplements—give their body exactly what it needs in the form it can best utilize.

References:

Geleijnse, J.M., et al. (2004). Dietary intake of menaquinone is associated with a reduced risk of coronary heart disease: the Rotterdam Study. Journal of Nutrition, 134(11), 3100–3105. PubMed

Knapen, M.H.J., et al. (2013). Three-year low-dose menaquinone-7 supplementation helps decrease bone loss in healthy postmenopausal women. Osteoporosis International, 24(9), 2499–2507. PubMed

Schurgers, L.J., et al. (2007). Vitamin K-containing dietary supplements: comparison of synthetic vitamin K1 and natto-derived menaquinone-7. Blood, 109(8), 3279–3283. PubMed

Vermeer, C. (2012). Vitamin K: the effect on health beyond coagulation – an overview. Food & Nutrition Research, 56, 5329. PubMed

Shea, M.K., & Booth, S.L. (2008). Update on the role of vitamin K in skeletal health. Nutrition Reviews, 66(10), 549–557. PubMed

Walther, B., et al. (2013). Menaquinones, bacteria, and the food supply: the relevance of dairy and fermented food products to vitamin K requirements. Advances in Nutrition, 4(4), 463–473. PubMed