Vitamin K often gets reduced to “the vitamin involved in blood clotting,” but that’s really only half the story. Vitamin K2, a specific form of vitamin K, plays a distinct role that’s drawn growing attention for bone and cardiovascular health. Here’s what it does and why it matters.
What Is Vitamin K2?
Vitamin K exists in two main forms: K1 (phylloquinone), found abundantly in leafy green vegetables, and K2 (menaquinone), found in smaller amounts in fermented foods and animal products like natto, aged cheese, egg yolks, and liver. While K1 is primarily used by the liver to support normal blood clotting, K2 is more actively involved in directing calcium to the right places in the body.
How Vitamin K2 Works
Vitamin K2 activates proteins — most notably osteocalcin and matrix Gla protein — that help regulate calcium in the body. Osteocalcin helps bind calcium to bone tissue, supporting bone mineralization, while matrix Gla protein helps prevent calcium from depositing in soft tissues like arterial walls. In simple terms, K2 helps ensure that calcium ends up in your bones rather than your blood vessels.
Why It’s Often Paired With Vitamin D
Vitamin D and vitamin K2 work in a complementary way: vitamin D increases calcium absorption from the digestive tract, while vitamin K2 helps direct that calcium toward bone rather than soft tissue. Because of this relationship, many supplement formulations now combine D3 and K2, on the theory that maximizing vitamin D’s benefits works best when there’s adequate K2 to help manage the resulting calcium.
Potential Benefits
Bone health. Some studies suggest vitamin K2 supplementation may support bone mineral density, particularly in populations with lower baseline K2 intake, though more research is needed to fully establish optimal dosing.
Cardiovascular health. Observational research has explored a relationship between higher vitamin K2 intake and reduced arterial calcification, based on its role in matrix Gla protein activation. This is an active area of ongoing research rather than a settled conclusion.
Dental health. Some early research has looked at vitamin K2’s role in supporting healthy tooth mineralization, though this area is less studied than bone and cardiovascular effects.
Dietary Sources
Vitamin K2 is less common in typical Western diets than K1, with natto (fermented soybeans) being by far the richest source. Other sources include:
- Hard and soft cheeses
- Egg yolks
- Chicken liver and dark meat poultry
- Butter and full-fat dairy from grass-fed animals
- Fermented foods like sauerkraut (in smaller amounts)
Because rich dietary sources are limited and vary in different subtypes of K2 (such as MK-4 and MK-7, which differ in how long they remain active in the body), many people choose to supplement, particularly if they’re also taking vitamin D3.
Considerations Before Supplementing
People taking blood-thinning medications such as warfarin should talk to a healthcare provider before taking vitamin K2 supplements, since vitamin K plays a role in blood clotting and can interact with how these medications work. As with most supplements, quality and third-party testing matter, given variability in dosing and form (MK-4 vs. MK-7) across products.
The Bottom Line
Vitamin K2 plays a distinct and increasingly recognized role in directing calcium toward bones and away from soft tissue, making it a useful complement to vitamin D in supporting long-term bone and cardiovascular health. If you’re already supplementing with vitamin D3, it’s worth considering whether your K2 intake is adequate as well.
This article is for informational purposes only and is not a substitute for professional medical advice.
