While the importance of vitamin D has become more fully appreciated, another vitamin that is just as important as vitamin D, vitamin K2, needs wider recognition. It’s a fat-soluble vitamin most well known for its role in blood clotting.

However, there are two primary kinds of vitamin K, and they serve very different functions.

Vitamin K1 is the primary form of vitamin K responsible for blood clotting, whereas vitamin K2 is essential for bone strength, the health of arteries and blood vessels, and plays a role in other biological processes as well, including tissue renewal and cell growth.

In the 2014 paper,¹ “Vitamin K: An old vitamin in a new perspective,” vitamin D expert Dr. Michael Holick and co-authors review the history of vitamin K and its many benefits, including its significance for skeletal and cardiovascular health. They also discuss important drug interactions.

Vitamins K1 and K2 Are Not Interchangeable

The difference between vitamins K1 and K2 was first established in the Rotterdam Study,² published in 2004. A variety of foods were measured for vitamin K content, and vitamin K1 was found to be present in high amounts in green leafy vegetables, such as spinach, kale, broccoli, and cabbage.

Vitamin K2, on the other hand, is only present in fermented foods. It’s produced by certain bacteria during the fermentation process. Interestingly, while the K1 in vegetables is poorly absorbed, virtually all of the K2 in fermented foods is readily available to your body.

Examples of foods high in vitamin K2 include raw dairy products such as certain cheeses, raw butter, and kefir, as well as natto (a fermented soy product) and fermented vegetables like sauerkraut.

However, not every strain of bacteria makes K2, so not all fermented foods will contain it. For example, pasteurized dairy and products from confined animal feeding operations (CAFOs) are NOT high in K2 and should be avoided. Only grass-fed animals (not grain fed) will develop naturally high K2 levels.

Most commercial yogurts are virtually devoid of vitamin K2, and while certain types of cheeses, such as Gouda, Brie, and Edam are high in K2, others are not. It really depends on the specific bacteria present during the fermentation.

One of the best sources I’ve found is to ferment your own vegetables using a special starter culture designed with bacterial strains that produce vitamin K2.

My research team found we could get 400 to 500 micrograms (mcg) of vitamin K2 in a two-ounce serving of fermented vegetables using such a starter culture, which is a clinically therapeutic dose.

Best yet, it is absolutely free if you use this starter culture. If you want to learn more about making your own fermented vegetables with a starter culture, you can watch the video and read more on this page.

https://www.youtube.com/watch?v=Ejzyt2Jp_bo