Is Vitamin K Synthesized by Intestinal Bacteria?

December 2, 2025 •

3 min read

According to research from the National Institutes of Health, bacteria in the large intestine produce a significant amount of vitamin K for the body. While a substantial portion of our vitamin K comes from dietary sources, particularly K1, the intestinal bacteria that synthesize vitamin K play a crucial, yet often underestimated, role in our overall nutritional status.

Quick Summary

The human gut microbiome produces menaquinones (vitamin K2), which can be absorbed and utilized by the body. This bacterially-derived vitamin complements dietary intake and is vital for blood clotting and bone health. Certain bacterial species are more efficient producers than others.

Key Points

Yes, intestinal bacteria synthesize vitamin K: Specifically, the gut microbiome produces menaquinones (vitamin K2) through microbial fermentation in the large intestine.
Endogenous production complements diet: This bacterial production serves as a supplementary source of vitamin K, especially beneficial when dietary intake of phylloquinone (K1) is insufficient.
Specific bacteria are responsible: Several species, including Escherichia coli, Bacteroides, Eubacterium, and Veillonella, are known producers of different menaquinone subtypes.
Absorption happens in the colon: Unlike dietary K1, which is absorbed in the small intestine, bacterially-produced K2 is absorbed in the colon via passive diffusion.
Gut health affects synthesis: Factors like prolonged antibiotic use or inflammatory bowel diseases can disrupt the gut microbiome, negatively impacting vitamin K synthesis.
Gut K2 has distinct functions: The K2 produced by gut bacteria is important for extra-hepatic functions, including bone and cardiovascular health, beyond the blood clotting function of K1.
Newborns lack this source initially: Infants are particularly susceptible to deficiency because their gut flora is not yet developed, necessitating a prophylactic vitamin K injection.

The Gut Microbiome: A Hidden Vitamin Factory

It is now widely established that the complex ecosystem of microorganisms residing in the human gut, known as the gut microbiome, is a critical contributor to our body's vitamin K supply. These organisms produce menaquinones (vitamin K2), one of the key forms of this essential nutrient. This production provides a supplement to the phylloquinone (K1) we obtain from our diet.

The Role of Intestinal Bacteria in Vitamin K2 Production

Intestinal bacteria synthesize menaquinones (MK-n), a family of vitamin K2 compounds. This synthesis is part of their own metabolic processes. The concentration and specific forms of K2 produced can vary between individuals, depending on their unique gut microbiome composition.

Several key bacterial species found in the human intestine are known to synthesize menaquinones, including:

Escherichia coli: Produces MK-8.
Bacteroides species: Produce longer-chain menaquinones like MK-10 and MK-11.
Eubacterium lentum: Synthesizes MK-6.
Veillonella species: Primarily produces MK-7.
Lactobacillus and Bifidobacterium: Some strains are producers, but with varying efficiency.

The absorption of this bacterially-produced vitamin K2 primarily occurs in the colon via passive diffusion. Dietary K1 is absorbed in the small intestine via a more active process.

Comparison of Dietary vs. Bacterially-Produced Vitamin K

Understanding the differences between dietary and endogenously-produced vitamin K is key. The table below highlights the major distinctions between these two sources.


Feature	Dietary Vitamin K (K1 and some K2)	Bacterially-Produced Vitamin K (K2)
Primary Form	Phylloquinone (K1) in plants, some menaquinones (K2) in fermented foods.	Menaquinones (MK-n), primarily synthesized by intestinal bacteria.
Absorption Site	Primarily absorbed in the small intestine.	Primarily produced and absorbed in the colon.
Absorption Mechanism	Active, carrier-mediated transport with the aid of bile salts.	Passive diffusion in the colon.
Bioavailability	Lower, often requiring fat for efficient absorption.	Variable; can be lower due to bacterial membrane binding, but longer-chain MKs can have better absorption properties.
Contribution	The major source of overall vitamin K intake, especially for K1.	An important supplementary source, especially significant when dietary intake is low.

Factors Affecting Gut Bacterial Vitamin K Synthesis

The efficiency of bacterial vitamin K production can be influenced by several factors:

Antibiotic Use: Can disrupt the gut microbiome, killing vitamin K-synthesizing bacteria, potentially leading to deficiency.
Gut Health: Conditions affecting fat malabsorption or inflammatory bowel diseases can interfere with absorption and microbiota composition.
Diet: Dietary fiber and prebiotics can support a healthy gut microbiome and influence vitamin K-producing bacteria.
Infancy: Newborn infants' gut flora is not fully developed, making them vulnerable to vitamin K deficiency. A prophylactic vitamin K injection is standard.

The Importance of the Intestinal Contribution

The menaquinones (K2) produced by intestinal bacteria have distinct functions from phylloquinone (K1) and are essential for extra-hepatic functions such as bone and cardiovascular health. A healthy gut microbiome ensures a consistent supply of K2, helping to minimize deficiency risk, especially during periods of low dietary intake. Disrupting this bacterial synthesis can have significant health implications, including an increased risk of bleeding. The symbiotic relationship between the host and its gut bacteria is vital for maintaining adequate vitamin K status. For more detailed information on vitamin K, consult authoritative health resources like the NIH Office of Dietary Supplements.

Conclusion

In conclusion, intestinal bacteria do synthesize vitamin K. This endogenous production of menaquinones (K2) by the gut microbiome is an important source of the vitamin for human health, complementing dietary intake. While dietary phylloquinone (K1) remains crucial, the bacteria in our large intestine provide a vital secondary supply, especially important for extra-hepatic functions. Maintaining a healthy, balanced gut flora is therefore essential for optimizing the body's overall vitamin K status and preventing potential deficiencies caused by factors like antibiotic use or poor diet. The symbiotic relationship between us and our intestinal bacteria highlights the profound connection between gut health and systemic nutrition.

Frequently Asked Questions

Intestinal bacteria synthesize vitamin K2, which is also known as menaquinone. This contrasts with vitamin K1 (phylloquinone), which comes primarily from plant-based foods.

No, the amount of vitamin K produced by intestinal bacteria is generally not enough to meet all of a person's needs. While it provides a significant contribution, especially K2, a healthy diet rich in vitamin K1 and other K2 sources is still necessary for optimal intake.

Several types of bacteria in the gut produce vitamin K, including Escherichia coli, Bacteroides species, Eubacterium lentum, and Veillonella. The specific subtypes of K2 (menaquinones) can vary depending on the bacterial species.

Long-term or broad-spectrum antibiotic use can disrupt and reduce the population of vitamin K-synthesizing bacteria in the gut. This can lead to a deficiency, especially if dietary intake of vitamin K is also low.

Vitamin K produced by gut bacteria in the colon is absorbed via passive diffusion, a process that is less efficient than the active transport mechanism used for dietary K1 absorption in the small intestine.

Newborn babies are given a prophylactic vitamin K injection because they have not yet developed the gut bacteria necessary for producing vitamin K. This prevents a potentially life-threatening bleeding disorder known as Vitamin K Deficiency Bleeding (VKDB).

Yes, chronic intestinal diseases or malabsorption issues can severely affect a person's vitamin K status. Poor fat absorption can hinder the uptake of both dietary and bacterial vitamin K, leading to deficiency.