What Vitamins Are Produced in the Gut?

The gut microbiome produces essential vitamins like K and B, but diet remains crucial to meet your daily needs. Discover which bacteria support vitamin synthesis and what can affect it.

Content Outline

• How does the gut microbiome produce vitamins?
• Key vitamins produced in the gut
  • Vitamin K
  • B vitamins
• Can gut bacteria fully meet our vitamin needs?
• The role of human milk oligosaccharides (HMOs) in supporting gut bacteria
• Conclusion

The human gut microbiome is home to trillions of microbes that play a vital role in digestion, immunity, and the production of essential nutrients. Among these nutrients are short-chain fatty acids (SCFAs) and vitamins.

Although the diet is the primary source of micronutrients, including vitamins, certain gut bacteria can produce them and contribute to your overall health and nutrition status.

Here, we explore the key vitamins synthesized by your gut microbiota, and identify the bacteria responsible for their production, before outlining some of the factors that influence microbial vitamin production.

How does the gut microbiome produce vitamins?

The gut microbiome consists of diverse bacterial species, many of which ferment or breakdown dietary components, most notably fiber. Through various metabolic processes, these bacteria can transform dietary components into useful metabolites, also known as postbiotics, like vitamins, and make them readily available for absorption in the colon.

Key vitamins produced in the gut

Some types of gut bacteria can produce essential vitamins our bodies need for:

• metabolic health
• immunity
• nutritional status
• general health and wellbeing

Essential vitamins are so-called because the human body can’t make them, so you must get them from your diet – or with a little help from your bacterial friends.

The key vitamins produced by the microbial residents in your gut are discussed in more detail below.

Vitamin K

Vitamin K is a fat-soluble vitamin that is crucial for:

• blood clotting – helps produce clotting factors to stop excessive bleeding after an injury[i]
• bone health – important for calcium absorption, strengthening bones, and preventing osteoporosis[ii]
• cardiovascular function – may prevent cardiovascular disease caused by clogged arteries[iii]

Emerging research suggests that vitamin K is also important for gut health, particularly in alleviating inflammatory bowel disease (IBD) and irritable bowel syndrome (IBS)[iv].

Similarly, small intestinal bacterial overgrowth (SIBO) can contribute to vitamin K deficiency. SIBO occurs when excessive numbers of bacteria colonize in the small intestine, disrupting digestion and nutrient absorption. Some bacterial species that contribute to SIBO may compete for vitamin K, resulting in deficiency, even if you have an adequate dietary intake[v].

There are two main forms of vitamin K:

1. Vitamin K1 (phylloquinone) – naturally present in green, leafy vegetables like spinach and kale and fruits like apples.
2. Vitamin K2 (menaquinone) – produced by gut bacteria and present in fermented foods and animal protein.

There are several different menaquinones, varying from MK-4 to MK-13. The abundance and concentrations of these different forms can vary between individuals and are dependent on the person's microbiome composition. Some of the major menaquinone producers are shown below[vi]:

 

B vitamins

B vitamins are a group of water-soluble nutrients that have numerous roles throughout the body. The B vitamin complex is essential, so it must be acquired from the diet, but there are several B vitamin producers in the gut.

However, the need for these essential micronutrients is a two-way affair. That’s because several gut bacteria need B vitamins. After all, they are necessary for the diversity and richness of the gut.

The table below outlines the key B vitamins produced by the gut microbiota[vii].

 

Can gut bacteria fully meet our vitamin needs?

The gut microbiome contributes to vitamin synthesis, and it’s believed that up to 50% of your daily vitamin K needs are provided by gut bacteria[viii]. However, it’s not healthy to solely rely on your gut to meet the body’s nutrient demands for several reasons. Perhaps the biggest reason is that the gut microbiome doesn’t synthesize all the essential vitamins your body requires.

Plus, the extent to which the vitamins it does produce are absorbed and used by the body depends on several factors, such as:

• Dietary intake – Eating a healthy balanced diet ensures adequate vitamin levels because bacterial synthesis alone may not produce large enough quantities. For example, the gut microbiome can make vitamins de novo, up to 30% of your daily requirements[ix], but this can depend on several factors including your diet[x]. So, dietary intake can help you meet your body’s vitamin needs, while many foods contain other important nutrients you need to thrive that your gut bacteria simply cannot produce.
• Gut microbiome composition – Individual differences in gut microbiome composition and diversity can impact vitamin synthesis. Some research shows that geographical location which heavily influences diet can impact vitamin production. For example, adults in the USA have lower capabilities to produce B vitamins[xi].  
• Gut health – An imbalanced microbiome (dysbiosis), inflammation, and infections can disrupt bacterial vitamin production and absorption. For example, conditions like IBD, IBS, and SIBO can affect your gut’s ability to synthesize vitamins.
• Competition – Some bacteria also need some of the vitamins that are produced by their comrades which inevitably means your body is competing for the nutrients. For example, while species like E. coli, and S. Typhimurium are busy making vitamin B5, other such as Lactobacillus helveticus need it for their own fatty acid and biotic metabolism[xii].

For these reasons, relying solely on your gut bacteria for vitamin production is not enough. Instead, a nutrient-rich diet packed with fruits, vegetables, wholegrain, lean proteins, and fermented foods will provide both the macro- and micronutrients your body needs for optimal health. It will also support a thriving gut microbiome to enhance overall vitamin synthesis and absorption.

The role of human milk oligosaccharides (HMOs) in supporting gut bacteria

Alongside your diet, supplements like human milk oligosaccharides (HMOs), can support a thriving bacterial community in your gut. HMOs are prebiotic compounds that are naturally present in breast milk and help to establish the early infant gut microbiome. However, they also have numerous benefits for adults, including shaping and diversifying their colonic bacterial community.

Research suggests that HMOs may support vitamin synthesis and absorption by:

• stimulating the growth of beneficial probiotics, particularly Bifidobacteria[xiii], which can synthesise many of the B vitamins de novo[xiv].
• enhancing the integrity of the gut barrier[xv] which may aid the absorption of several vitamins[xvi].
• stimulating the growth of specific species which can cross-feed others to stimulate their growth and activity, which may increase the production of specific metabolites[xvii].

Conclusion

The gut microbiome has a crucial role in synthesizing vitamins, especially vitamin K and B vitamins. However, while the microbiota contributes to the overall availability in the body, dietary intake is essential for maintaining optimal health.

Supporting your gut health through a fiber-rich diet, probiotics, and prebiotics like HMOs, may enhance microbial vitamin production and absorption and promote your overall wellbeing.

Written by: Leanne Edermaniger, M.Sc. Leanne is a professional science writer who specializes in human health and enjoys writing about all things related to the gut microbiome.  

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