What Is Vitamin K2 and Why Does It Matter?

Most people have heard of Vitamin K. Far fewer know there are two very different forms of it – and that the one most people are missing is not the one found in leafy greens.

Vitamin K2 is one of the more underappreciated nutrients in the supplement world. It does not make headlines in the same way as Vitamin D or Vitamin C – but it plays a specific and important role in how calcium is used in the body. And that has real implications for your bones, your cardiovascular health, and how well your other supplements actually work.

It is also why we added it to the new formulation of Immunity + Vitality.

Here is what K2 does, why it matters, and why we think it belongs in a daily supplement.

Vitamin K2 vs Vitamin K1 – what is the difference?

Vitamin K is a family of fat-soluble vitamins that share a similar structure but have quite different roles in the body.

Vitamin K1 (phylloquinone) is found in leafy green vegetables – kale, spinach, broccoli. Its main job is blood clotting: it activates the proteins that stop wounds from bleeding. If you eat a reasonably varied diet, you are probably getting enough K1.

Vitamin K2 (menaquinone) is found in fermented foods and some animal products – and its job is entirely different. Where K1 keeps your blood behaving as it should, K2 is concerned with where calcium goes once it is in your bloodstream.

The two forms most commonly seen in supplements are:

• MK-4 – a shorter-chain form found in animal products, faster acting but shorter lived in the body
• MK-7 – a longer-chain form derived from fermented foods (particularly natto), which stays active in the body significantly longer and is the form used most widely in high-quality supplements

They are not interchangeable. MK-7 is generally considered the more effective form for daily supplementation because of its longer half-life.

What does Vitamin K2 actually do?

Think of K2 as a traffic director for calcium – making sure it ends up where it should, and not where it shouldn't.

Vitamin D pulls calcium from your gut into your bloodstream. That is one of its primary functions and one of the main reasons Vitamin D is so widely recommended. But increased calcium absorption only benefits you if that calcium is correctly directed once it is circulating in the body.

This is where K2 comes in. It activates two proteins that are central to this process:

• Osteocalcin – produced by bone-building cells, responsible for binding calcium into the bone matrix. Without sufficient K2, osteocalcin remains inactive and cannot anchor calcium into bone effectively.
• Matrix Gla Protein (MGP) – found in arterial walls and soft tissue, MGP helps prevent calcium from depositing in places it should not be, including arteries.

Without adequate K2, the calcium mobilised by Vitamin D does not necessarily end up in your bones. It can accumulate in soft tissue instead – which is clearly not the goal.

This is a significant distinction, and one reason why Vitamin D and K2 are increasingly discussed as a pair rather than as separate nutrients.

How the calcium team works

Think of it as a three-part system:

• Vitamin D promotes the initial absorption of calcium from the digestive tract into the bloodstream.
• Calcium is the primary mineral responsible for building and maintaining bone structure.
• Vitamin K2 activates the proteins that physically bind circulating calcium into the bone matrix – while simultaneously preventing it from accumulating in arterial walls.

Each one plays a different part. Focusing on just one without considering the others is a bit like building a house with bricks but no mortar and no architect.

Why this matters for bone health

Bone is not static. It is constantly being broken down and rebuilt in a process that relies on calcium being available and correctly placed.

K2 supports osteocalcin, the protein that makes this process work properly. Research has associated adequate K2 intake with better bone mineral density, and it is widely considered to contribute to normal bone maintenance over time.

For those focused on long-term bone health – particularly postmenopausal women, where bone loss becomes a more pressing concern – this is a meaningful piece of the picture.

Why this matters for cardiovascular health

This is where K2 really distinguishes itself.

The same calcium-directing function that benefits bones is also relevant to arterial health. By activating Matrix Gla Protein (MGP) in the arterial walls, K2 may help prevent calcium from depositing where it should not be.

Studies, including large European cohort research, have observed associations between higher dietary K2 intake and markers of cardiovascular health. To be clear: K2 is not a treatment for cardiovascular disease. But the research does suggest it may support healthy arterial function as part of a balanced diet and lifestyle.

Two meaningful areas. One mechanism.

Vitamin K2 and Vitamin D – why they work together

If you take Vitamin D (and in the UK, most adults should be, especially through the autumn and winter months), K2 is a nutrient worth paying attention to.

Vitamin D increases calcium absorption from the gut. More calcium in the bloodstream is generally the goal. But that calcium needs to be directed correctly – and without K2, there is no guarantee it ends up where it is needed.

Some researchers now consider K2 to be an important companion to Vitamin D supplementation for precisely this reason. A formula that includes D3 without K2 is working with only part of the picture.

This is one of the reasons we reformulated Immunity + Vitality to include K2 alongside D3. It was a deliberate choice, not an addition for its own sake.

Vitamin K2 and other nutrients

K2 does not work in isolation. Several nutrients interact with the same calcium pathways.

Vitamin A

Along with D and K2, Vitamin A is a fat-soluble nutrient involved in calcium regulation and immune function. The three appear to work synergistically – which is reflected in how a well-designed multi-nutrient formula should be structured.

Magnesium

Magnesium is required for converting Vitamin D into its active form in the body. Without sufficient magnesium, D3 supplementation may be less effective than expected. Since D3 and K2 work closely together, magnesium sits in the background as an important supporting player in this whole system.

This is why single-nutrient thinking often falls short. The body works in networks, not in isolation.

Food sources of Vitamin K2

Vitamin K2 is not easy to get in meaningful amounts from a typical Western diet. The richest sources include:

Fermented foods

• Natto (fermented soya beans) – by far the highest food source, but rarely eaten in the UK
• Aged cheeses, particularly Gouda and Brie
• Fermented dairy products
  
  

Animal products

• Egg yolks, particularly from pasture-raised hens
• Chicken liver and other organ meats
• Butter and full-fat dairy from grass-fed animals

The challenge is consistency. K2 content in animal products varies significantly depending on how the animals were raised and fed, and the amounts in most foods are modest. Natto aside, getting reliable, meaningful levels of K2 through diet alone is genuinely difficult for most people eating a typical UK diet.

Who might benefit from supplementing with K2?

Most healthy adults eating a varied diet will get some K2 through food – but consistent intake at meaningful levels is hard to achieve without supplementation. It is particularly worth considering if you:

• Take Vitamin D supplements regularly
• Are focused on supporting long-term bone health
• Follow a plant-based or vegan diet, as K2 food sources are predominantly animal-derived
• Are postmenopausal
• Eat little to no fermented food

As always, if you have specific health concerns or are on medication, speak to a healthcare professional before making changes to your supplement routine. The same applies if you are considering supplements for children – always seek professional guidance on appropriate dosing.

Why we added K2 to Immunity + Vitality

Immunity + Vitality already contained Vitamin D3 – and D3 without K2 is a gap that became harder to justify the more we looked at the research.

The new formulation adds Vitamin K2 (MK-7) to a formula that already includes Vitamin D3, Vitamin A, Zinc, Selenium, Reishi mushroom, Cranberry Extract, and Alpha Lipoic Acid.

Every ingredient in that list earns its place. The K2 addition is not there for label appeal. It is there because D3 and K2 work as a pair, because the calcium-directing mechanism matters, and because a formula built around immune and vitality support should reflect how these nutrients actually function together in the body.

It is a better formula because it is a more complete one.

Immunity + Vitality is available in Orange & Mango and Raspberry & Lemon.

For more on the other ingredients in the formula, take a look at our articles on Vitamin D and why we need it, the benefits of Zinc for immunity, and why Reishi mushroom is in our formula.

This article is for informational purposes only and does not constitute medical advice. Supplements should be taken as part of a balanced diet and healthy lifestyle. If you have any health concerns or are taking medication, please consult a healthcare professional before use.