We heard from lots of you that you want to learn more about Vitamin K2, so here is an introduction to this underappreciated nutrient.

Some of you may be familiar with this basic background info, so we’ve also provided opportunities to dig deeper with links to further articles and primary scientific research literature. Others who may come to natto as a source of probiotics or nattokinase may find a whole new reason to love it!

There’s so much to share and more new information about Vitamin K2 being discovered every year, so we’ll take it one bite-size piece at a time! Subscribe to our newsletter for the latest updates, we’ll focus in on one particular health disorder/disease state and its relationship to Vitamin K2, sharing current views and data from recent science. Find our newsletter sign-up form in the footer of this page.

Why is Vitamin K2 important?

Vitamin K2 is a critical dietary micronutrient that is virtually absent in the modern Western diet. Any comprehensive discussion of Vitamin K2 will include mention of Natto, as this unique food is well known to be the absolute richest food source of Vitamin K2.

Vitamin K2 is receiving more and more attention in medical and nutrition circles because of growing evidence that Vitamin K2 may be a pivotal factor in the prevention of osteoporosis as well as cardiovascular & coronary disease, kidney disorders, diabetes and cancer.

How can all these common chronic diseases be linked to Vitamin K2, a micronutrient that most people haven’t even heard of? Because K Vitamins are critical cofactors for a variety of Vitamin K-dependent proteins (VDKs) in the body, including factors involved in blood clotting but also many others involved in calcium transport as well as insulin regulation, fat deposition, cell proliferation and DNA transcription.

What is Vitamin K?

There is a lot of confusing information about Vitamin K out there in the infosphere. Much of this confusion arises from the unclear nomenclature of Vitamin K and all of its different isoforms. Whenever you see information or intake recommendations regarding “Vitamin K”, this usually refers to both K1 and K2 collectively. Since Vitamin K2 is present in such vanishingly small amounts in most foods, unless otherwise specified, “Vitamin K content” practically always means ‘only Vitamin K1’.

Like the B vitamins, the term “Vitamin K” actually refers to a family of related molecules that can be broadly divided between Vitamin K1 (phylloquinone) and Vitamin K2 (menaquinone).

The confusing history & nomenclature of K vitamins

As you can see below, all the Vitamin K family members share a similar chemical structure. They all contain in common a napthoquinone double ring on the left of these drawings attached to varying types of side chains. Although there is some overlap in physiological functions for the various Vitamin K types, Vitamin K2 appears to play little role in blood clotting and instead is best known to function in regulating calcium transport within the body. Many additional physiological functions of K Vitamins are actively being studied.

Vitamin K2 (MKs or menaquinones) can further be subdivided into a family of closely related molecules that differ in the length of their side-chain structure.

The simplest and shortest of the menaquinones is MK-4, extending up to MK-14, though MK-10-14 have been found only at very low levels in some fermented foods. Among the MK isoforms of K2, MK-4 and MK-7 are the best studied and the only two that are available also in supplement form.

Among the MK isoforms of K2, MK-4 and MK-7 are the best studied and the only two that are available also in supplement form.

In supplements, MK-4 is a synthetic compound.

MK-7 is still commercially produced by purification from bacterial natto fermentation.

It matters what kind of vitamin K we get. The slightly differing structures of these Vitamin K molecules affect how they each function and distribute themselves within the body and in the foods they’re found in.

What foods are good sources of Vitamin K?

We humans need to take in K Vitamins through food. These fat-soluble vitamins are essential nutrients that we cannot make by ourselves. We must rely on other organisms that we ingest to provide them for us. Vitamin K1 and K2 are found in very different food sources. Further, specific types of MK menaquinones also appear in different types of foods.

Food sources of Vitamin K from chrismasterjohnphd.com

What foods contain Vitamin K1?

Vitamin K1 is only made by plants where it functions in electron transport during plant photosynthesis and thus is found in abundance in green, leafy vegetables. Common dark leafy greens like spinach or collard greens contain upwards of 500 micrograms of K1 per 100g. As long as you are including green vegetables in your diet, Vitamin K1 deficiency is rare; Vitamin K2 is a different story.

What foods contain Vitamin K2?

Most forms of Vitamin K2 can be made only by bacteria, where it functions in electron transport in energy metabolism (analogous to K1’s role in bacteria-derived plant chloroplasts). Thus, Vitamin K2 can be consumed in the form of fermented foods such as natto, and European hard cheeses. But different fermented foods contain wildly differing amounts of Vitamin K2. For example, Natto contains about 15x times more Vitamin K2 as the best cheese sources and ~200x times as much as sauerkraut!

The exception is MK-4, which animals and humans can synthesize in small amounts from dietary Vitamin K1 phylloquinone or menadione. How much MK-4 can be generated has been estimated to range from 5% to 25% of the ingested phylloquinone, but this provides neither the levels nor diversity and distribution of menaquinones needed to fully support all Vitamin K2-dependent functions throughout the body.

This is why measurable amounts of MK-4 can be found in fatty dairy and meat-based foods. Herbivorous animals like cattle ingest large amounts of plant Vitamin K1 and can convert some of it to MK-4. K vitamins are fat-soluble and therefore accumulate most in fat-rich tissues, organs (like liver, brain) and milk.

Some cheeses, because they are further fermented with microbes which also produce significant amounts of longer chain forms of MK menaquinones have additional VItamin K2 content. Even among cheeses, there is a lot of variation in how much K2 is present—dependent on the quality of the milk (grass-fed, quality milk will begin with higher K1 & MK-4 content) and the particular strains of microbes used to produce the cheese (different bacterial strains & species vary greatly in their ability to synthesize various MK isoforms).

How much Vitamin K2 do I need?

The USDA has not yet established a Recommended Daily Allowance (RDA) for Vitamin K. The US Institute of Medicine has set an Adequate Intake (AI) at 90 and 120 micrograms per day for adult women and men. However, this recommendation is based on phylloquinone (K1) and its required levels for proper regulation of blood clotting, as the primary form of Vitamin K in the Western diet. This Vitamin K AI does not address dosage requirements for K2 menaquinones because (a) sufficient food composition analyses of K2 content in Western foods and (b) new science demonstrating the specific importance of K2 menaquinones in calcium regulation, bone & cardiovascular health did not yet exist at the time.

So long story short: there still is no government-sanctioned intake recommendation specifically for Vitamin K2, but scientists are working on it! For now, medical advocates of Vitamin K2 generally recommend amounts comparable to those established for Vitamin K1 (~100 micrograms or more daily) for healthy adults. For those at risk for bone loss (osteoporosis, osteopenia, arterial calcification, kidney stones) or seeking other Vitamin K2-dependent health benefits, higher amounts may be needed.

How much natto should you eat to get your daily dose of K2? A single tablespoon of natto contains more than 150 micrograms of Vitamin K2 as MK-7 along with Bacillus subtilis probiotics, nattokinase enzyme in the natural context of a nutritious, protein-rich whole food. Take a look at our Natto Recipes page for ideas on how to eat more natto.

Why is Vitamin K2 Deficiency so prevalent?

There are many factors that contribute to Vitamin K2 deficiency; one of the most important is diet. The modern American food system and typical Western diet have made it more difficult to take in adequate amounts of dietary Vitamin K2.

In the West, major dietary sources of MK-4 include animal-based foods in the form of meat, organ & dairy products. As is true for many nutrients, the MK-4 content of these foods can be highly dependent on exactly how the animals are raised and fed. Pastured and grass-fed animals will naturally take in much more Vitamin K1, a starting material which can be converted to MK-4, from the plant matter they eat. As more and more meat and dairy animals are factory farmed and grain-fed, they lose Vitamin K1 and therefore also Vitamin K2 MK-4 content.

Longer chain menaquinones (e.g. MK-7, 8, 9) are produced naturally by probiotic bacteria (e.g. Bacillus subtilis) and accumulating to significant levels in some fatty fermented foods. Certain cheeses, again ideally made from grass-fed, Vitamin K1-rich milk, have significant levels of higher MK menaquinones made by fermenting bacteria during cheese production. Living, probiotic fermented foods once had a significant presence in culinary traditions of almost every culture around the world. The modern industrially produced diet has limited access to many of these natural menaquinone food sources from our food system.

As you can see from the bar chart below showing the relative Vitamin K1 & K2 contents of top food sources, nothing even comes close to natto!

Natto is the BEST Source of Vitamin K2, particularly for bones

Natto contains far more Vitamin K2 than any other food ever tested. It is also the only significant plant-based, vegan food source of Vitamin K2 available. About 90% of Natto’s K2 is in MK-7 form, the type of menaquinone which has the strongest evidence for bone health benefit.

Numerous observational and interventional clinical studies have shown convincing correlations between dietary Vitamin K2 intake and lower bone fracture rates and higher bone density mass (BDM), particularly in post-menopausal women. Research shows that natto is a great food for bone health.

Precisely how Vitamin K2 helps build healthy bone and prevent bone loss will be the focus of our next science update in a few weeks. We’ll present a summary of current clinical research data showing the remarkable correlations between dietary Vitamin K2 (in the form of food) and bone strength and density.

Disclaimer: Statements in this article are the summary of our evaluation of scientific literature and have not been evaluated by the FDA. This product is not intended to diagnose, treat or cure disease.

Natto & the Science of Vitamin K2