What is Vitamin K2, and What Role Does It Have in Health?

Vitamin K is well-known for its role in blood clotting, but the less well-known vitamin K2 may have important roles in bone health or even heart disease.

When people think about vitamin K, they might think about the shot infants get in their foot right after birth because their bodies can’t make the vitamin yet. Some might know that the vitamin is important for clotting, especially if they have ever known someone on blood thinning medications like warfarin.

Beyond that, it seems like even nutrition professionals rarely talk about vitamin K, but this may be changing as we learn more about vitamin K2.

What is vitamin K2 and what does it do?

Only in recent decades have scientists found that vitamin K1 and K2 have different functions. They both have roles as ‘on’ switches for functions in our body, but have different targets.

In the liver, vitamin K1 activates proteins that help with blood coagulation. For example, think about when you get a cut in your skin. Your skin will typically bleed for a short time, but soon stops. This is due to your body turning on processes that coagulate the blood at the wound, which slows or stops the flow. Without vitamin K1 activating these proteins, our blood would be unable to clot. Vitamin K1 may also have a role in bone health, similar to that of vitamin K2 described below.

Vitamin K2 helps turn on processes outside of the liver, like in our bones or our blood vessels. In blood vessels, it activates a protein called Matrix Gla-protein (MGP) which removes calcium from the lining of blood vessels. This is important for heart health, as calcification of blood vessels is a risk factor for heart disease. In bones, it activates osteocalcin, a bone-forming protein. It is an important nutrient for bone health because it helps our bones draw calcium from our blood vessels and turn it into bone tissue.

How does vitamin K2 interact with other bone health nutrients like calcium and vitamin D?

It is thought that calcium, vitamin D, and vitamin K2 act synergistically for bone health. Calcium is the main building block of our bone tissue. When we eat food rich in calcium, it goes through our digestive tract where it is digested and absorbed in our small intestine. Calcium is needed for other bodily functions, and if we don’t get it from our diet our body pulls it from ‘storage’ i.e. our bones. This is why calcium deficiencies in the diet can lead to conditions like osteoporosis (bone disease that occurs when the body loses too much bone, makes too little bone, or both) – we are pulling more from our bones than we are putting in. It might be helpful to think of it like a bank: sometimes you put money in, sometimes you take money out, but when you constantly take more out than you put in, it can lead to bad things down the road.

Calcium can be hard for our bodies to absorb and utilize, but that is where vitamin D can help by improving our body’s ability to absorb calcium from our diet more efficiently. It also prevents our body from removing calcium from our bones when we are getting enough elsewhere. In other words, vitamin D signals to our body that calcium is available from a food source. In the banking analogy, think of vitamin D like a notification that a paycheck is coming. When you get the notification, you can anticipate what to do with the money and you also know you don’t need to withdraw from your savings.

Vitamin K2 helps with the next step. Once you’ve eaten a high calcium food and vitamin D has helped you absorb it, your body will have calcium flowing through your blood vessels. It is thought that vitamin K2 may help our bones draw this calcium out of our blood stream and deposit it into bone tissue. Think of it like a teller at a bank that performs the act of depositing your paycheck into your bank account.

What does vitamin K2 have to do with heart disease?

Vitamin K2’s role in heart health is also related to calcium. In the development of atherosclerosis – a disease in which plaque builds up inside your arteries –  those plaques can break loose and form a blockage in a blood vessel. When that blockage happens in an artery that supplies blood to the heart, it causes a heart attack. These plaques are partly made of calcium. Calcium deposits in arteries have been shown to be a risk factor for heart disease.

Vitamin K2 activates a protein that removes calcium from blood vessels. Higher vitamin K2 intake has been shown to be linked to decreased heart disease risk, as a result.

This makes a complicated picture for bone health and heart health. Many people may not be aware of the interconnected roles of vitamin K2 and vitamin D in bone health, and instead will focus on increasing calcium intake. If they are deficient in vitamin K2, though, this has the potential to lead to more calcium deposits in blood vessels and leading to a higher risk of heart disease. More research is needed to fully understand this complicated relationship.

Where do we get vitamin K2 in our diets?

The best sources of vitamin K2 are animal foods, specifically meat, egg yolks, and high fat dairy products. Many animals can convert vitamin K1 into vitamin K2, which is why animal foods can be a good source of this nutrient.

Some of the best sources of vitamin K2 originate from microbes like bacteria. This means that certain fermented foods like cheese, curd, and natto (fermented soybeans) are some of the best sources of vitamin K2. Natto contains significantly more vitamin K2 than any other food source (over 20x more than cheese).

Since vitamin K2 can originate from bacteria, the question ‘what about our own microbiome?’ might come to mind. Research shows that the microbes in our colon are capable of producing vitamin K2, but current studies show it’s unlikely we absorb it.

How much vitamin K2 do we need, and do we get enough of it?

There is no formal recommendation for vitamin K2 intake, since the body of research about this nutrient is still growing. The Rotterdam study in 2005 (4807 men and women) showed that the average intake for vitamin K2 was 28.5 micrograms per day, and it seems to be those who consume more might be healthier. The same study showed those consuming >32.7 micrograms per day had lower measures of cardiovascular disease risk factors than those consuming <21.6 micrograms per day.

Clinical trials testing health benefits of vitamin K2 can use doses ranging from 50 to 300 micrograms per day. Without a formal recommendation or a universal method of testing whether someone is deficient, though, it remains to be seen how big of a worry vitamin K2 is.

Looking to the future

Vitamin K2 has grown rapidly over the past 5-10 years in the dietary supplement industry, where many food and beverage trends begin. Although there isn’t much talk about vitamin K2 in the food and beverage industry yet, there are opportunities.

The first and possibly largest opportunity is making vitamin K2 available in more food sources, through fortification or formulation with vitamin K2-rich foods. If research continues to show a unique and important role of dietary vitamin K2 in health, this means that people are limited to animal sources to get this nutrient with the sole exception of natto. Recommendations to reduce meat or high fat dairy intake are prevalent globally, and so many people try to avoid the best sources of vitamin K2. Vegetarians and vegans are even further restricted in the food source options for this nutrient.

Adding vitamin K2 to a wider variety of plant-based products can help address this gap. In addition, natto has a much higher vitamin K2 content compared to most animal sources, however many of the studies showing a benefit of vitamin K2 for bone or heart health use natto as the vitamin K2 source. It may be difficult for people to meet these effective doses of vitamin K2 in their diet without consuming natto, so foods and beverages that provide a higher functional dose of vitamin K2, such as with fortification, could be an effective route for the industry to improve consumer health.

• Nathan Pratt, PhD, RD

  Nathan Pratt, PhD, RD is a nutrition scientist passionate about helping people use science to lead better lives. He completed his doctoral studies at the University of Illinois at Urbana-Champaign, where his research focused on weight management, nutrition labeling, and consumer behavior. He joined Kerry’s nutrition team in 2016 is responsible for scientific communications, nutrition-related innovation and guidance on product development.