Can K1 be Converted to K2? Unpacking the Vitamin K Conversion Process

December 25, 2025 •

4 min read

While most people are aware of Vitamin K's importance for blood clotting, far fewer understand that Vitamin K is actually a family of compounds. Specifically, this includes Vitamin K1 (phylloquinone) from plants and Vitamin K2 (menaquinones) from fermented foods and animal products. The question of whether the body can convert one form to another is critical for ensuring optimal intake.

Quick Summary

The body can convert Vitamin K1 to K2, specifically to the MK-4 subtype, but this process is limited and inefficient. Dietary intake of K2, especially the long-chain MK-7 found in fermented foods, is crucial for sufficient levels that support extra-hepatic functions like bone and heart health.

Key Points

Conversion is Limited: While your body can convert some K1 into K2 (MK-4), the process is inefficient and likely doesn't produce enough for optimal health.
Source Matters: Vitamin K1 from leafy greens is primarily used by the liver for blood clotting, whereas K2 from fermented foods and animal products supports bones and arteries.
Gut Bacteria Help: Beneficial gut bacteria contribute to the production of certain K2 menaquinones, underscoring the importance of a healthy gut microbiome.
Bioavailability Differences: K2, particularly the MK-7 subtype, has a longer half-life and is more bioavailable than K1, allowing for better distribution throughout the body.
Dietary Intake is Key: The most reliable way to ensure sufficient levels of both K1 and K2 is through a diverse diet that includes both leafy greens and fermented or animal-based foods.

Understanding the Vitamin K Family

Before delving into the conversion process, it is important to understand the different forms of Vitamin K. Vitamin K is a fat-soluble vitamin essential for producing proteins involved in blood clotting, bone metabolism, and heart health. The two most prevalent natural forms are Vitamin K1 and Vitamin K2.

Vitamin K1 (Phylloquinone): Predominantly found in plant-based foods, especially green leafy vegetables like kale, spinach, and broccoli. Its primary role is in the liver, where it helps produce proteins for blood coagulation.
Vitamin K2 (Menaquinones): Primarily found in animal products and fermented foods, where it is synthesized by bacteria. Vitamin K2 includes several subtypes, or menaquinones (MKs), most notably MK-4 and MK-7, which have different side-chain lengths and functions. K2 is distributed to extra-hepatic tissues, such as bones and blood vessels, where it activates proteins for calcium utilization.

The Conversion of K1 to K2: A Limited Process

Yes, the human body can convert Vitamin K1 into Vitamin K2, but this conversion is not as straightforward or efficient as many believe. Research has confirmed that Vitamin K1 is converted into the MK-4 subtype of Vitamin K2 in specific tissues, including the pancreas, testes, and arterial walls. The mechanism involves removing the side chain of K1 and then reattaching a shorter chain to create MK-4, a process that does not rely on gut bacteria.

However, this conversion pathway has significant limitations that make dietary intake of K2 crucial:

Inefficient Absorption: The absorption of K1 from plant sources is often poor, with studies suggesting less than 10% is absorbed by the body. This is because K1 is tightly bound to plant cell membranes.
Limited Supply: The amount of K2 produced from K1 conversion may be insufficient to meet the body's needs for extra-hepatic functions, like activating proteins for bone and cardiovascular health.
Different Functions: While K1 primarily supports liver functions for blood clotting, K2 has broader roles. Longer-chain K2 forms, like MK-7, are known to have a longer half-life in the bloodstream, allowing for more effective distribution to extra-hepatic tissues.

K1 vs. K2: A Comparison of Functions and Sources


Feature	Vitamin K1 (Phylloquinone)	Vitamin K2 (Menaquinones)
Primary Source	Leafy green vegetables (kale, spinach, broccoli)	Fermented foods (natto, cheese), animal products (egg yolks, liver, dark meat chicken)
Absorption	Poorly absorbed from plant sources; improves with dietary fat	Better absorbed, especially when consumed with fat
Half-Life	Short half-life, clears from blood quickly (hours)	Long half-life for longer-chain forms (days)
Distribution	Primarily transported to and used by the liver for blood clotting	Redistributed from the liver to extra-hepatic tissues (bones, arteries)
Main Function	Blood coagulation	Bone mineralization and preventing arterial calcification

The Role of Gut Bacteria and Dietary Intake

While the internal conversion of K1 to MK-4 is a key mechanism, gut bacteria also play a role in producing different forms of Vitamin K2. The length of the menaquinone side chain determines its biological activity and distribution within the body. Longer-chain MKs, such as MK-7 found in fermented soybeans (natto), are known for their enhanced bioavailability and ability to reach extra-hepatic tissues, which is why they are often recommended in supplements.

For most people, relying solely on the body's limited conversion process is not enough to maintain optimal Vitamin K2 status for long-term bone and cardiovascular health. This is particularly true for individuals with low dietary intake of K2-rich foods or those taking blood-thinning medication.

To ensure adequate intake, a diverse diet including both plant-based K1 sources and animal or fermented K2 sources is recommended. Additionally, consuming K1-rich vegetables with a source of fat can enhance its absorption. For those with dietary restrictions or specific health concerns, supplementation may be necessary, but should be discussed with a healthcare provider, especially when taking other medications.

Conclusion

In short, while the body possesses the ability to convert K1 into K2, specifically the MK-4 subtype, this process is generally inefficient and insufficient to cover all of the body's needs. The conversion is not a reliable source for the long-chain menaquinones like MK-7, which are crucial for bone and cardiovascular health. Therefore, for optimal health, it is important to consume both K1-rich foods and K2-rich foods, or consider supplements, rather than relying solely on the body's internal conversion of K1.

This article is for informational purposes only and does not constitute medical advice. Consult with a healthcare professional before making any dietary changes or starting new supplements.

A Balanced Diet Is Crucial

List of Dietary Sources

Vitamin K1 (Plant-Based):

Kale
Spinach
Broccoli
Brussels sprouts
Swiss chard

Vitamin K2 (Fermented & Animal-Based):

Natto (fermented soybeans)
Cheeses (Gouda, Brie, Edam)
Egg yolks
Organ meats (liver)
Dark meat chicken
Sauerkraut

Final Thoughts on Supplementation

For those concerned about meeting their Vitamin K needs, particularly K2, supplements can be a viable option. Many supplements offer K2 in the form of MK-7, which is known for its high bioavailability and long half-life, ensuring it reaches extra-hepatic tissues effectively. However, it is essential to consult a doctor, especially if you are taking blood-thinning medication like warfarin, as Vitamin K can interfere with its effects. Consistent intake is key, and healthcare guidance ensures a safe and effective approach to supplementation.

NIH Office of Dietary Supplements provides additional information on Vitamin K intake and sources.

Frequently Asked Questions

Vitamin K1 (phylloquinone) is found in plants and primarily supports blood clotting in the liver. Vitamin K2 (menaquinones) is found in animal and fermented foods and supports bone and cardiovascular health in other tissues.

No, while your body can convert some K1 from leafy greens into K2 (MK-4), this process is limited and inefficient, and the K2 produced may not be sufficient for all bodily functions.

Vitamin K2 activates proteins like osteocalcin, which helps direct calcium into bones to improve density and strength. K1 does not have the same significant effect on bone health.

Rich sources of K2 include natto (fermented soybeans), hard cheeses, egg yolks, and organ meats. The specific K2 subtype can vary by food source.

Many experts suggest combining K2 with Vitamin D3, as they work synergistically. Vitamin D aids calcium absorption, and K2 helps direct that calcium to the correct places, like bones, rather than arteries.

Yes, Vitamin K plays a role in blood clotting and can interfere with the effectiveness of anticoagulant medications like warfarin. Anyone on blood thinners should consult a doctor before increasing Vitamin K intake.

Vitamin K1 deficiency is rare, but insufficient levels of K2 are more common, especially in Western diets that lack fermented foods. Low K2 levels may manifest as long-term issues like arterial calcification, which can be hard to detect early.