You are not alone if you’ve never heard of Vitamin K2. Maybe you’ve heard of “Vitamin K” as the coagulation vitamin – but that is mainly the job of Vitamin K1. Vitamin K2 seems to be a big secret! So let’s get talking about it and see how important it is for getting calcium to the places in the body where we want it.  

The K vitamins

The K vitamins are a group of fat-soluble vitamins (like vitamins A, D, and E). The two most important forms are Vitamin K1 (phylloquinone) and Vitamin K2 (menaquinone).

  • Vitamin K1 is known for its role in blood coagulation.  
  • Vitamin K2 comes in different forms such as MK4 or MK7. It has an essential role in building and maintaining strong bones and also inhibiting calcium deposits in the arteries and blood vessels. 

Why has K2 been overlooked?

It’s a case of mistaken identity. 

Vitamin K was discovered in the 1930s. Although two types were identified, it was thought that both types did the same thing – namely, were involved in coagulation. (The “K” comes from the German word Koagulation.)   

Unlike other fat-soluble vitamins, we don’t store vitamin K1 in our body. This might make you think that it might be easy to get deficient in this important vitamin if we don’t eat good food source every day. However, because the coagulation function is so vital, the body’s work-around is to recycle its K1. Therefore deficiency is rare, even if we don’t eat K1 food sources daily.

Early research thought K2 was similar to K1, and that you couldn’t be deficient in K2 either. But it turns out that K2 has many distinct actions in the body entirely separate from coagulation. It wasn’t until 2007 that more information was discovered and it was determined that it is possible to  have a K2 deficiency without having a bleeding/coagulation disorder.

K2 deficiency is actually quite wide-spread. So what are the symptoms?

Symptoms of K2 Deficiency

  • osteoporosis
  • atherosclerosis
  • dental caries (cavities), crowded teeth
  • prostatitis
  • prostate cancer
  • varicosities (varicose veins)
  • insulin resistance
  • cancer – particularly lung and prostate
  • osteophytes (bone spurs)
  • kidney stones

The Calcium Paradox

The first two symptoms on this list – osteoporosis, and atherosclerosis – are the basis of the ‘calcium paradox’ that we have been struggling with for years. 

The ‘calcium paradox’ term was coined when researchers observed that some postmenopausal women taking calcium supplements had an actual loss in bone mineral density (the opposite of what was expected) but had increased arterial calcification. The calcium was not getting to the bones where it was needed and was instead accumulating in the blood vessels.

Osteoporosis – lack of calcium where it is needed.

Image of bone density changes from

Atherosclerosis – an excess of calcium where it is not needed.

Image showing calcification of arteries from

The most recent meta-analysis (combining the results of several different studies) of trials of calcium supplements found a 27-31% increase in the risk of heart attack and a 12-20% increase in the risk of stroke.

Millions of people take calcium supplements for bone health and to prevent osteoporosis. And, of course, we’ve been told to drink more milk for calcium. We’ve gone from 800mg… 1000mg…to 1200mg….to 1500mg extra calcium a day – but osteoporosis hasn’t improved. Even when it is combined with adequate vitamin D levels and supplemental magnesium, the calcium is not going where it is needed. What’s going on?

Enter Vitamin K2

The missing link to explain the calcium paradox is Vitamin K2. It is like a traffic policeman, directing the calcium to the bones and teeth and just as importantly, away from the blood vessels. And large studies have shown this. 

Atherosclerosis – In the Rotterdam study, a ten-year study on 7,983 men and women over 55 years old, higher K2 intake had a strong protective effect on cardiovascular health. Eating food rich in K2 resulted in a 50% reduction in arterial calcification and death due to cardiovascular disease!

Osteoporosis – In the Nurses’ health study and the Framingham Heart study, people with lower intake of dietary vitamin K2 had a greater risk of fractures, including hip fractures. 

How does K2 work?

If you have been taking calcium supplements or your family has a history of cardiovascular disease, you may have calcium building up in your arteries. But this can be reversed. Our body has mechanisms to do this, but it needs the right nutrients.

Vitamin K2 acts in association with certain proteins that are calcification inhibitors. Three of these are called Osteocalcin, Matrix Gla Protein (MGP), and Gas6. MGP is the strongest inhibitor of soft tissue calcification presently known. But for these proteins to do their job and get the calcium into the correct parts of the body, they need Vitamin K2 to activate them.  

Even if we have high levels of these proteins in our vessels, they are inactive if there is a deficiency of K2. The K2 activation stops calcification in the vessels.

Here’s a little video of these actions:

What’s gone wrong that we don’t get adequate K2 in our diet?

Several factors have affected our K2 intake. These include:

  • Industrial farming. Grazing animals eating green leafy veg get good levels of Vitamin K1 from the greens, which they can convert into K2 (humans can’t convert significant amounts of K1 into K2). But we have moved many animals that we consume from pasture to grain feeding. Thus the animals no longer get the K1 from the grass and so can’t convert it to K2, and therefore there are reduced K2 levels in animals. Dairy, egg yolks, and organ meats used to be good sources of K2 – but are not if the animals are grain fed. If you eat one dozen eggs a day from caged hens, you don’t get enough K2 for your daily requirement. If you eat only two eggs a day from pasture raised hens, you get adequate amounts of K2!
  • We are eating less fermented food. In the case of K2, our refrigerator is not our friend! Some bacteria in fermented foods make K2. Before we had refrigeration, we consumed much more fermented food, because that is how we had to store it. Even though we no longer have to eat fermented food, we can choose to do so. Examples of fermented foods that are good sources of K2 include sauerkraut, brie, and gouda cheese. 
  • Consumption of trans fats blocks the action of K2. While trans fat consumption is now reducing, this has been a factor in our diets. 
  • Certain medications deplete K2 or inhibit its absorption:
      • statins
      • broad spectrum antibiotics
      • cholestyramine and colestipol, bile acid sequestrants
      • orlistat – a weight-loss drug (Alli) which reduces absorption of fat-soluble vitamins, including vitamin K.

Where do we get K2 from?

There are two main natural sources of vitamin K2 – food and bacteria. These are often combined as in the case of fermented foods where it is the bacteria in the food that have created the K2. 

Sources include:

  • natto (bacteria)
  • pasture raised chickens and eggs (food from K1 conversion to K2 in animals)
  • gouda and brie cheese (bacteria)
  • sauerkraut (bacteria) 
  • butter from grass fed cows (food from K1 conversion to K2 in animals)

You might not be familiar with natto. It is the best-known food source of K2. Natto is fermented soybeans, a dish popular in Japan. But it is generally not suited to our palates. The photo at the top of this blog is of the gooey mess of natto. It’s definitely an acquired taste because of its powerful smell, strong flavor, and slimy texture. It’s normally eaten for breakfast! Ugh, not a popular choice! If you want to give it a try, you can find it in the frozen section of many Asian grocery stores…but maybe some of those other foods are easier choices for us.

Next week’s blog post will look at how much K2 we need every day and whether we can get enough from our food or whether we need to supplement. We’ll also cover the different types of K2  and what to look for in a supplement. 

Have you ever tried natto? What did you think?

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