Can humans convert vitamin K1 to K2? Understanding the conversion process

December 5, 2025 •

3 min read

While vitamin K is a fat-soluble nutrient essential for blood clotting, it is composed of two primary forms: K1 (phylloquinone) and K2 (menaquinones). Though the body can synthesize some vitamin K2 from K1, the process is not always efficient enough to meet all of the body's needs.

Quick Summary

The human body has a limited and inefficient ability to convert vitamin K1 (phylloquinone) from plants into vitamin K2 (menaquinone-4), while gut bacteria also produce other K2 forms. This process depends on gut health and dietary factors, making direct dietary intake of K2 from animal and fermented foods important for health.

Key Points

Limited Conversion Efficiency: The human body can convert vitamin K1 to K2 (specifically MK-4), but this metabolic process is inefficient and does not meet all needs.
Gut Bacteria Contribution: In addition to internal conversion, gut bacteria synthesize other forms of vitamin K2, though their overall contribution to body stores is unclear and variable.
Different Functions: Vitamin K1 is primarily associated with blood clotting, while vitamin K2 is more critical for bone and cardiovascular health, supporting calcium metabolism.
Factors Impacting Absorption: Absorption is enhanced by dietary fats and a healthy gut microbiome, and can be hindered by low-fat diets, certain medications, and intestinal issues.
Direct Intake Recommended: Because conversion is insufficient, consuming direct dietary sources of K2, such as fermented and animal products, is important for maintaining optimal levels.

The Biological Basis for Vitamin K1 to K2 Conversion

Humans possess the metabolic machinery to convert vitamin K1 (phylloquinone) into a specific subtype of vitamin K2, known as menaquinone-4 (MK-4). This conversion process occurs within various tissues, including the pancreas, brain, and testes. Research involving stable isotope tracers in animal models has provided significant insight into the biochemical steps involved. It has been shown that phylloquinone is first broken down into an intermediate compound, menadione (vitamin K3), through the removal of its side chain. This menadione molecule is then used to synthesize the new menaquinone-4 molecule by adding a new isoprenoid side chain. This process is independent of the gut microbiota and represents a critical internal pathway for producing the highly bioavailable MK-4 form.

The Role of Gut Bacteria in Vitamin K2 Production

Beyond the body's internal conversion of K1 to MK-4, certain gut bacteria also play a vital role in synthesizing various other forms of vitamin K2, known as long-chain menaquinones (e.g., MK-7 through MK-13). These forms are produced in the large intestine from both dietary K1 and other bacterial processes. The efficiency of this bacterial production can be influenced by the composition and balance of the gut microbiome. For example, the use of broad-spectrum antibiotics can disrupt the delicate balance of gut flora, potentially leading to a decrease in endogenous K2 production. However, it is still uncertain how much of this bacterially produced K2 is actually absorbed and utilized by the body, highlighting the importance of dietary sources.

The Inefficiency of Human Conversion

Despite the existence of these conversion pathways, the overall efficiency of transforming dietary vitamin K1 into usable K2 is considered low. The body absorbs only a fraction of the vitamin K1 present in plant foods like leafy greens, as it is tightly bound within the plant's chloroplasts. For instance, studies suggest that the body absorbs significantly less phylloquinone from spinach compared to a vitamin K supplement. This low bioavailability, combined with the inefficient metabolic conversion, means that relying solely on K1 intake is unlikely to provide sufficient levels of K2, especially for its systemic functions in bone and cardiovascular health.

Factors Affecting Conversion and Absorption

Numerous factors can impact the conversion and absorption of vitamin K:

Dietary Fat Intake: As a fat-soluble vitamin, both K1 and K2 require dietary fat for optimal absorption in the small intestine. Low-fat diets can significantly hinder this process.
Gut Microbiome Health: The type and diversity of bacteria in the gut influence the production of menaquinones. A healthy, balanced gut flora promotes better K2 synthesis.
Intestinal Health: Conditions that affect intestinal health, such as Crohn's disease or celiac disease, can impair nutrient absorption, including vitamin K.
Antibiotic Use: Prolonged or frequent use of broad-spectrum antibiotics can suppress the gut bacteria responsible for producing K2.
Medications: Certain medications, including bile acid sequestrants and some fat-blocking drugs, can interfere with vitamin K absorption.

Comparing K1, K2, and the Conversion Process


Feature	Vitamin K1 (Phylloquinone)	Vitamin K2 (Menaquinones)	Conversion from K1 to K2
Primary Source	Green leafy vegetables	Fermented foods, animal products	Internal process and gut bacteria
Main Function	Primarily blood clotting	Bone and cardiovascular health	Inefficiently produces MK-4
Absorption Rate	Low bioavailability from plants	Higher bioavailability, especially MK-7	Highly variable, depends on health
Body Storage	Short half-life, primarily stored in the liver	Longer half-life, stored in various tissues	Leads to MK-4 storage in specific tissues
Health Effects	Blood coagulation	Reduces vascular calcification, improves bone density	Limited contribution to systemic K2 levels

Conclusion

While the human body does have the capacity to convert vitamin K1 to K2, specifically to the MK-4 subtype, this process is notably inefficient. The conversion, along with the production of other K2 forms by gut bacteria, is not sufficient to rely on as a sole source for the broader, systemic benefits associated with vitamin K2, such as promoting bone density and preventing arterial calcification. Optimal health requires a balanced approach that includes both abundant dietary sources of K1 from vegetables and direct intake of K2 from animal products, fermented foods, or supplements to ensure adequate levels for all bodily functions.

Here is a source discussing the conversion process via a menadione intermediate.

Frequently Asked Questions

Vitamin K1 (phylloquinone) is mainly found in leafy green vegetables and is primarily involved in blood clotting. Vitamin K2 (menaquinones), found in fermented foods and animal products, is more active in regulating bone health and preventing arterial calcification.

No, relying solely on the body's conversion of K1 is insufficient. The process is inefficient, and the K2 produced may not be enough to support optimal bone and cardiovascular health, necessitating direct dietary intake of K2.

Certain bacteria in the large intestine produce various forms of vitamin K2 (long-chain menaquinones) from dietary sources. However, the amount absorbed is unclear and can be affected by factors like antibiotic use and gut health.

Vitamin K1 is abundant in leafy green vegetables like kale and spinach. Vitamin K2 is found in fermented foods like natto, certain cheeses, and animal products like grass-fed dairy, egg yolks, and organ meats.

Vitamin K is a fat-soluble vitamin. It requires the presence of dietary fats to be properly absorbed by the small intestine. Low-fat diets can therefore impair vitamin K absorption.

While it can lead to some increase in MK-4 through the conversion process, a vitamin K1 supplement is unlikely to provide sufficient levels of K2. Directly supplementing with or consuming K2 is a more effective way to increase K2 status.

You can support the process by maintaining a healthy and balanced gut microbiome through a diet rich in fiber and fermented foods, limiting antibiotic use when possible, and ensuring you consume enough dietary fat.