What is vitamin K produced from? A Comprehensive Guide to its Diverse Origins

January 6, 2026 •

4 min read

Over half of all bacterial species produce menaquinones, a form of vitamin K. This guide will delve into what is vitamin K produced from, exploring the origins of its different forms and how the human body utilizes them from various food sources.

Quick Summary

Vitamin K originates from two primary natural sources: plants synthesize K1 (phylloquinone), and bacteria produce K2 (menaquinone), which is also found in fermented foods and animal products.

Key Points

Plant Sources (K1): Phylloquinone (K1) is produced exclusively by plants during photosynthesis and is found in green leafy vegetables and vegetable oils.
Bacterial Sources (K2): Menaquinones (K2) are primarily produced by bacteria, making fermented foods like natto and cheese a rich source.
Dual Origin : Vitamin K's diverse forms, K1 and K2, come from fundamentally different biological production processes in plants and microbes, respectively.
Bioavailability Differences: Vitamin K2 (especially MK-7) has a longer half-life and is considered more bioavailable than K1, which affects how it's used in the body.
Endogenous Conversion: The body's own tissues, such as the pancreas and testes, can convert vitamin K1 into the menaquinone-4 (MK-4) form, a process independent of gut bacteria.
Limited Gut Contribution: While our gut bacteria produce some K2, its absorption is limited, making dietary sources essential for meeting our vitamin K needs.
Synthetic Form: A synthetic form of vitamin K, menadione (K3), is used as an intermediate in animal feed, but is no longer used in human supplements due to toxicity concerns.

Vitamin K is a fat-soluble vitamin essential for several vital bodily functions, including blood clotting, bone metabolism, and cardiovascular health. The story of its production is not singular; it is a tale of different forms—known as vitamers—emerging from distinct biological processes and sources. The two most significant natural forms are vitamin K1 (phylloquinone) and vitamin K2 (menaquinone), each produced by different organisms. Understanding their origins is key to appreciating how a diverse diet contributes to our overall health.

Vitamin K1: The Plant-Derived Form

Phylloquinone, or vitamin K1, is synthesized exclusively by plants, where it plays a critical role in the process of photosynthesis. It is found in the highest concentrations within the chloroplasts of photosynthetic tissues. This makes leafy green vegetables and other green plant parts the primary dietary source of vitamin K1 for humans.

How Plants Produce Phylloquinone

In green plants, phylloquinone functions as an electron acceptor in Photosystem I, a light-dependent reaction that is a fundamental step in photosynthesis. Because of this vital role, the vitamin is present in substantial quantities in any plant part with high chlorophyll content. The biosynthesis pathway converts precursors like chorismate into the final phylloquinone molecule.

Dietary Sources of Vitamin K1

Some of the best food sources for phylloquinone include:

Green leafy vegetables: Kale, spinach, collard greens, Swiss chard, and turnip greens.
Cruciferous vegetables: Broccoli, Brussels sprouts, and cabbage.
Vegetable oils: Soybean oil, canola oil, and olive oil contain vitamin K1, and adding a fat source to vegetables improves absorption.

Vitamin K2: The Bacterial-Derived Form

Menaquinones, collectively known as vitamin K2, are primarily synthesized by bacteria through a different metabolic pathway. These bacteria produce menaquinones for use in their own electron transport chains, enabling anaerobic respiration. This microbial origin means that we obtain vitamin K2 through certain fermented foods and, to a lesser extent, from our own gut microbiota.

The Role of Bacteria in Vitamin K2 Synthesis

The production of menaquinones is a common capability among many bacteria. Specific species involved include:

Bacillus subtilis: This bacterium is used to ferment soybeans to make natto, a Japanese food that is one of the richest dietary sources of menaquinone-7 (MK-7).
Lactococcus lactis and Propionibacterium: These and other lactic acid bacteria (LAB) are used in the production of various cheeses and other fermented dairy products, which contain different menaquinone subtypes like MK-8 and MK-9.

The Gut Microbiota and K2

While many intestinal bacteria, including strains of E. coli and Bacteroides, can synthesize menaquinones, the contribution of this internal production to a person's overall vitamin K status is still debated. Absorption of these menaquinones is thought to be inefficient due to their production location in the large intestine, where bile salts necessary for absorption are less abundant. Therefore, dietary intake of K2 remains the most reliable source for this form of the vitamin.

The Unique Case of Menaquinone-4 (MK-4)

Menaquinone-4 (MK-4) is a unique subtype of vitamin K2. Unlike the long-chain menaquinones produced by bacteria, MK-4 is predominantly synthesized by animals through a conversion process. Animal tissues, particularly the testes, pancreas, and arterial walls, can convert phylloquinone (K1) into MK-4. This conversion is not dependent on gut bacteria and explains why MK-4 is found in animal-sourced foods like meat, eggs, and dairy, even if the animal's diet was rich in plant-based K1. MK-4 is also formed in animals by converting the synthetic form, menadione.

Comparison of Vitamin K1 and Vitamin K2 Sources


Feature	Vitamin K1 (Phylloquinone)	Vitamin K2 (Menaquinone)
Primary Natural Source	Synthesized by plants during photosynthesis.	Synthesized by bacteria.
Key Dietary Sources	Green leafy vegetables, vegetable oils, some fruits.	Fermented foods (natto, cheese), animal products (meat, eggs, dairy).
Primary Forms	One single compound, phylloquinone.	A series of subtypes (MK-4 through MK-13).
Half-Life in Body	Short half-life, a few hours.	Longer half-life, especially for long-chain MKs like MK-7.
Bioavailability	Lower absorption from plant sources unless consumed with fat.	Often considered more bioavailable due to better absorption and longer circulation time.
Primary Bodily Function	Supports blood clotting factors synthesized in the liver.	More widely distributed and plays significant roles in bone and cardiovascular health.

How the Body Gets Vitamin K

Most of our vitamin K intake comes from dietary sources. The fat-soluble nature of the vitamin means it is absorbed in the small intestine, requiring the presence of bile and pancreatic juices for optimal uptake. The primary pathway is consuming vitamin K1 from plant sources and vitamin K2 from fermented and animal foods. While gut bacteria do synthesize some menaquinones, their contribution is considered minimal because production occurs mainly in the large intestine, past the main absorption site in the small intestine. Some of the ingested K1 is converted into the MK-4 form in the body's tissues.

Conclusion

In summary, the origin of vitamin K is not monolithic, but rather a dual system involving both plant and bacterial synthesis. Phylloquinone (K1) comes directly from plants, particularly leafy greens, and is most recognized for its role in blood coagulation. Menaquinones (K2), which have varying subtypes, are produced by bacteria and are abundant in fermented foods and animal products; they are linked more strongly to bone and cardiovascular health. The body also performs its own conversion, transforming K1 into the highly-bioavailable MK-4 variant. A balanced diet rich in both plant-based and fermented/animal products is therefore the most effective way to obtain the full spectrum of vitamin K for optimal health. For more detailed information on vitamin K and its functions, refer to trusted nutrition resources such as the Linus Pauling Institute at Oregon State University.

Frequently Asked Questions

The two primary natural forms are vitamin K1 (phylloquinone), found in plants, and vitamin K2 (menaquinone), produced by bacteria.

Vitamin K1 is produced by plants during photosynthesis. The main dietary sources are green leafy vegetables such as kale, spinach, and broccoli, as well as some vegetable oils.

Vitamin K2 is primarily synthesized by bacteria. It is abundant in fermented foods, especially natto, and is also found in animal products like eggs, meat, and cheese.

While intestinal bacteria produce menaquinones (K2), their contribution to your total vitamin K status is minimal. This is because absorption primarily occurs further up in the small intestine, and diet is the most reliable source.

Both forms are important and serve different functions. K1 is vital for blood clotting, while K2 is more involved in bone and cardiovascular health. K2 (specifically MK-7) is considered more bioavailable with a longer half-life.

MK-4 is a unique form of vitamin K2 that is produced by animal tissues converting vitamin K1 or a synthetic precursor called menadione, not by gut bacteria.

The absorption of vitamin K1 from plant sources can be poor unless consumed with fat. K2, especially the long-chain versions like MK-7, is generally absorbed better and stays in circulation longer.

Newborns have low vitamin K levels due to poor placental transfer. A vitamin K injection is administered to prevent Vitamin K Deficiency Bleeding (VKDB), a dangerous bleeding disorder.