Where is vitamin K mostly produced? A guide to its sources and synthesis

December 11, 2025 •

4 min read

Approximately 25% of our vitamin K, specifically menaquinones (K2), may be supplied by the helpful bacteria living in our gut. This article answers the question, 'where is vitamin K mostly produced?' by exploring the dual origins of its main forms, K1 and K2, which come from both plants and bacterial synthesis.

Quick Summary

Vitamin K is produced by plants (K1) and gut bacteria (K2). Dietary intake from green vegetables, fermented foods, and animal products also provides a vital supply of this essential vitamin.

Key Points

Dual Production: The two main forms of vitamin K are produced by different sources: K1 by plants and K2 primarily by bacteria.
Plant-Based K1: Vitamin K1 (phylloquinone) is made by plants and is most abundant in dark, green leafy vegetables like spinach and kale.
Bacterial K2: Vitamin K2 (menaquinone) is produced by bacteria, including the beneficial microbes residing in the human large intestine.
Dietary Sources: Important food sources of K2 include fermented foods like natto, as well as certain animal products like liver and cheese.
Diet and Bacteria Together: While gut bacteria produce some K2, a substantial portion of the body's total vitamin K supply must come from a diet rich in both plant-based K1 and other K2 sources.
Absorption Matters: For fat-soluble vitamin K, consuming plant sources with a bit of fat (e.g., oil) enhances absorption into the body.

The Dual Origins of Vitamin K

Vitamin K is not a single compound but a group of fat-soluble vitamins essential for blood clotting and bone health. The two most significant naturally occurring forms are phylloquinone (vitamin K1) and a series of menaquinones (vitamin K2). The answer to where this vitamin is mostly produced depends on which form you are discussing, as each has a distinct origin. While plants are the exclusive producers of vitamin K1, bacteria are the sole producers of most menaquinone subtypes (K2), including those residing in the human gut.

Vitamin K1: A Product of Photosynthesis

Phylloquinone, or vitamin K1, is synthesized exclusively by plants and algae, playing a key role in photosynthesis. Because of this, it is found in the highest concentrations in the green, photosynthesizing parts of plants.

Key sources of vitamin K1 include:

Dark, leafy greens: Kale, spinach, turnip greens, collard greens, and romaine lettuce are some of the most concentrated sources.
Cruciferous vegetables: Broccoli, Brussels sprouts, and cabbage also contribute significant amounts.
Other vegetables: Vegetables such as asparagus and leafy parts of spring onions contain K1.
Some plant oils: Soybean and canola oil are good sources of phylloquinone.
Fruits: Smaller amounts are present in some fruits, like kiwi and blueberries.

An important factor for dietary K1 absorption is its fat-soluble nature. Consuming these foods with a small amount of dietary fat, such as adding olive oil to a salad, can significantly improve its bioavailability.

Vitamin K2: The Bacterial Connection

Menaquinones, or vitamin K2, are primarily synthesized by bacteria. This includes both food fermentation processes and the activity of the microorganisms that make up our intestinal flora. The different menaquinone subtypes (designated MK-4 through MK-13) have varying side chain lengths, which affect their biological activity and distribution in the body.

Key sources of vitamin K2 include:

Gut Microbiota: The bacteria in the large intestine, including E. coli and Bacteroides, are known to synthesize menaquinones. While the exact contribution of this internal production to overall vitamin K status is debated, it is believed to satisfy at least some of the body's requirements.
Fermented Foods: Traditional Japanese food natto, made from fermented soybeans, is an exceptionally rich source of menaquinone-7 (MK-7). Other fermented products like hard and soft cheeses also contain significant amounts of menaquinones, depending on the bacterial strains and fermentation process.
Animal Products: Meats, especially liver and poultry, as well as egg yolks, contain menaquinone-4 (MK-4). This form is created in animal tissues from the dietary conversion of vitamin K1, a process that does not require gut bacteria.

K1 vs. K2: A Comparison of Sources


Feature	Vitamin K1 (Phylloquinone)	Vitamin K2 (Menaquinone)
Primary Producers	Plants (for photosynthesis)	Bacteria (gut microbiota, fermentation)
Primary Dietary Source	Dark green leafy vegetables	Fermented foods and animal products
Best Food Examples	Kale, spinach, collard greens, broccoli	Natto, hard cheeses, egg yolks, liver
Synthesis in Humans	Not directly synthesized	Synthesized by gut bacteria; MK-4 is converted from K1 in tissues
Key Functions	Mostly involved in blood clotting	Important for bone metabolism and cardiovascular health in addition to clotting
Bioavailability	Relatively low from vegetables, improved with fat	Varies depending on the source; MK-7 from natto is highly bioavailable

The Role of Dietary vs. Endogenous Production

While the human gut synthesizes vitamin K2, this endogenous production alone may not be sufficient to meet all the body's needs. Our overall vitamin K status relies on a combination of dietary intake and bacterial synthesis. Factors like prolonged antibiotic use can disrupt the gut microbiota, reducing the internal production of vitamin K2 and potentially leading to a deficiency, especially if dietary intake is also low. For this reason, a balanced diet rich in varied vitamin K sources is the most reliable way to ensure adequate intake. For most healthy adults, consuming a varied diet provides all the necessary vitamin K, and supplementation is generally not required unless there is an underlying health condition or medication interference.

To learn more about vitamin K, its functions, and potential deficiencies, consult this authoritative resource: Vitamin K - Health Professional Fact Sheet

Conclusion: A Diverse Production Chain

Ultimately, vitamin K is mostly produced by both the plant and bacterial kingdoms, making it a nutrient with diverse origins. Vitamin K1 is manufactured by plants and is abundant in green leafy vegetables. Vitamin K2, conversely, is the product of bacterial activity, found in fermented foods, some animal products, and synthesized by the microorganisms living within our intestines. A healthy, balanced diet containing a mix of both plant and animal-based foods remains the best way to ensure your body receives a steady supply of this crucial fat-soluble nutrient.

Frequently Asked Questions

Our gut bacteria, primarily in the large intestine, produce menaquinones, which are a form of vitamin K2.

Yes, humans can produce a portion of their own vitamin K, but only the K2 form and indirectly. The menaquinone (K2) synthesized by gut bacteria is absorbed, and the body can also convert some dietary K1 into menaquinone-4 (MK-4) in certain tissues.

The primary source of vitamin K1 (phylloquinone) is plants, especially dark, green leafy vegetables such as kale, spinach, and collard greens.

Yes, fermented foods are a key source of vitamin K2. A notable example is natto, a Japanese fermented soybean dish, which contains very high amounts of menaquinone-7 (MK-7).

Yes, for most healthy people, a varied and balanced diet that includes plenty of green vegetables, fermented foods, and some animal products can provide all the vitamin K needed.

Vitamin K is a fat-soluble vitamin, so it is best absorbed when consumed with dietary fat. It is absorbed in the small intestine and transported via the lymphatic system.

Prolonged antibiotic use can disrupt the gut microbiota, which may reduce the endogenous production of vitamin K2. In such cases, maintaining adequate dietary intake becomes even more important.