Which vitamin K is important? Separating K1 and K2 Roles

January 11, 2026 •

2 min read

Vitamin K is a fat-soluble nutrient that is crucial for several key functions within the human body. Research indicates that the two main forms, K1 and K2, each have distinct roles that impact blood clotting, bone density, and cardiovascular health.

Quick Summary

The vitamin K family comprises K1 and K2, each with unique biological functions. K1 is essential for blood clotting, while K2 supports bone and heart health. Both are vital for well-being, though deficiencies can impact different body systems.

Key Points

Both are Important: Vitamin K1 is vital for blood clotting, and K2 is essential for bone and heart health.
K1 for Clotting: Vitamin K1, found in leafy greens, is used by the liver for blood-clotting proteins.
K2 for Calcium: Vitamin K2, in fermented foods and animal products, directs calcium to bones and prevents artery buildup.
Dietary Differences: K1 is in plants, while K2, with various subtypes, is in fermented and animal foods and has better bioavailability.
K2's Longer Life: K2 circulates longer, allowing it to benefit tissues like bones and blood vessels more.
Balance is Key: A diet with K1-rich vegetables and K2-rich fermented and animal products is recommended.

The Vitamin K Family: K1 vs. K2

Vitamin K isn't a single nutrient, but a family of compounds. The two most studied forms are Vitamin K1 (phylloquinone) and Vitamin K2 (menaquinones). They have distinct sources and roles in the body. K1 comes mainly from leafy green plants and is used by the liver for blood-clotting proteins. K2 is found in animal products and fermented foods and supports bone and cardiovascular health outside the liver.

Vitamin K1: The Blood-Clotting Essential

Vitamin K1 is vital for blood coagulation. It enables the production of key clotting factors, preventing excessive bleeding. Newborns receive K1 injections for this reason. Consistent K1 intake is important for adults, especially those on blood thinners like warfarin.

Vitamin K2: The Bone and Heart Protector

Vitamin K2 supports the long-term health of bones and arteries. It activates proteins like osteocalcin for bone calcium binding and matrix GLA protein (MGP) to prevent calcium buildup in arteries. This calcium management is key for skeletal and cardiovascular health. Low K2 levels are linked to fracture risk and arterial calcification.

The K1 to K2 Conversion

The body can convert K1 to K2 (MK-4), but this conversion is limited and often insufficient for K2's functions outside the liver. This makes dietary K2 sources, like fermented foods and animal products, important for bone and heart health. K2 forms, especially MK-7, have a longer half-life, allowing them to benefit other tissues more effectively than K1.

Comparison of Vitamin K1 and K2


Feature	Vitamin K1 (Phylloquinone)	Vitamin K2 (Menaquinone)
Primary Function	Blood clotting.	Bone health and cardiovascular protection.
Main Food Sources	Leafy green vegetables (kale, spinach), broccoli, Brussels sprouts.	Fermented foods (natto), cheese (Gouda), egg yolks, and organ meats.
Bioavailability	Poorly absorbed from plant sources; estimated less than 10%.	Generally better absorbed, especially when consumed with fats.
Distribution	Primarily retained and used by the liver.	Redistributed to extra-hepatic tissues like bones and blood vessels.
Half-Life	Short; typically circulates for only a few hours.	Longer; some forms like MK-7 can stay in the blood for days.

How to Ensure You Get Both Important Forms

For optimal health, ensure a balanced diet with both K1 and K2. Dietary K1 alone is insufficient for K2's benefits. Consider these tips:

Eat Your Greens: Include leafy greens daily, cooked with fat to improve K1 absorption.
Explore Fermented Foods: Natto is rich in K2 (MK-7). Aged cheeses and some sauerkraut also contain K2.
Include Animal Products: Pasture-raised egg yolks, grass-fed butter, and organ meats provide K2 (MK-4).
Consider Supplements: Supplements with K1 and K2 (MK-7) may help those with dietary restrictions, but consult a healthcare provider first.

Conclusion: The Combined Importance of K1 and K2

Both K1 and K2 are important, each with distinct roles. K1 is crucial for blood clotting, while K2 supports bone and arterial health by managing calcium. A balanced diet including leafy greens, fermented foods, and certain animal products is the best approach for comprehensive wellness.

For more information, consult resources like the National Institutes of Health.

Frequently Asked Questions

The main difference lies in their functions and sources; K1 aids blood clotting (leafy greens), while K2 supports bone and heart health (fermented foods, animal products).

While K1 is common in the diet, K2 can be harder to obtain. If your diet lacks these foods, a supplement could be useful, but consult a healthcare provider first.

Vitamin K2 is more closely linked to bone health than K1. It activates proteins that guide calcium to bones, aiding bone density and reducing fracture risk.

Yes, you can obtain enough vitamin K from a balanced diet, including leafy greens for K1 and fermented foods, eggs, or animal products for K2. Pairing with fat improves absorption.

Yes, Vitamin K2 is vital for heart health. It activates proteins that stop calcium buildup in arteries, helping prevent cardiovascular disease.

A K1 deficiency can cause blood clotting issues and bleeding. Insufficient K2 intake may contribute to poor bone mineralization and increased arterial calcification over time.

Good sources of Vitamin K2 include natto (fermented soybeans), cheeses, egg yolks, and organ meats.