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Do gut bacteria produce vitamin B12?

The human body is a complex ecosystem teeming with billions of microorganisms. Among these, gut bacteria play an important part in our general health and well-being. Vitamin B12 is present in tiny amounts in food and is used as a dietary supplement.

One fascinating subject that has piqued researchers’ interest is whether gut bacteria can manufacture vitamin B12 (cyanocobalamin or cobalamin), a key component required for a variety of human processes.

Vitamin B12: Functions and Sources

Vitamin B12, commonly known as cobalamin, is a water-soluble vitamin that is essential for deoxyribonucleic acid (DNA) synthesis, the creation of red blood cells, and brain function. Vitamin B12 is also involved in the formation of short-chain fatty acids (SCFAs) such as propionate, which improve gut function and general health.

Vitamin B12 deficiency can lead to anemia, tiredness, weight loss, constipation, depression, memory difficulties, tingling in the hands and feet, and other clinical presentations of neurological disorders.

This vitamin is mostly found in animal products such as fish, liver, meat, chicken, dairy, and eggs. As a result, those who eat a vegetarian or vegan diet may have difficulty getting enough vitamin B12 from their food.

Vitamin B12 in the Gut

The ability of the human body to synthesize vitamin B12 is limited, and the liver retains only a small quantity of this essential component. This begs the issue of whether gut bacteria, which live in the complex environment of the digestive system, can synthesize vitamin B12 and contribute to our overall B12 requirements.

The link between Gut microbes and Vitamin B12 production

According to research, certain bacteria in the human stomach may manufacture vitamin B12. However, the quantity they produce may be insufficient to fulfill the body’s daily needs. Certain kinds of bacteria from the genera Bacteroides and Firmicutes, which are often found in the human digestive tract, are the principal producers of B12. Research indicates that Bacteroidetes encode a unique family of vitamin B12-binding proteins known as BtuH, which are necessary for effective B12 transport and competitive fitness in the gut.

Researchers have stated that around 20% of gut bacteria can manufacture vitamin B12, while over 80% of gut bacteria require B12 for metabolic processes. A review published in 2019 in the Frontiers of Nutrition reported that the following gut microbes can synthesize vitamin B12:

  • Firmicutes: Faecalibacterium prausnitzii, Clostridium difficile, Lactobacillus plantarum, Ruminococcus lactaris, L. reuteri, and L. coryniformis.
  • Bacteroidetes Prevotella copri and Bacteroides fragilis
  • Fusobacteria: Fusobacterium varium
  • ActinobacteriaBifidobacterium infantis, B.longum, and B. animalis.

While these bacteria can produce B12, this vitamin is mostly absorbed in the small intestine, and B12 produced by gut bacteria in the large intestine (colon) may be too far downstream (below the ileum) to be properly absorbed.

In other words, B12-producing bacteria are found in the large intestine, but vitamin B12 receptors are exclusively found in the small intestine, where they absorb dietary B12 following protein breakdown in the stomach. As a result, the gut microbial B12 is not bioavailable to the host. This theory is reinforced by the fact that numerous vegetarian animal species ingest their feces, allowing them to obtain B12. Coprophagy is the act of consuming excrement by mammals such as hippos, rabbits, elephants, pandas, and non-human primates when they are deficient in vitamin B12.

Furthermore, the host’s and gut bacteria’s fight for B12 absorption may reduce the quantity accessible for absorption by the host. Studies have reported that the abundance and diversity of gut microbiota are linked to vitamin B12 levels and obesity.

Probiotics such as Bacillus megaterium, Propionibacterium freudenreichii, and Pseudomonas denitrificans are known to produce vitamin B12 commercially. B12 generated by anaerobic indigenous gut microorganisms is required for probiotics to improve host resistance to pathogen infections. Furthermore, as a gut microbial regulator, B12 demonstrated the potential to improve connections between gut microbiota and tight junctions in the gut, hence enhancing host resistance to pathogen infection.

Factors that influence vitamin B12 synthesis by gut microbes

Gut bacteria produce vitamin B12, which is not produced by host cells. Several factors, including diet, the makeup of the gut microbiome, and the individual’s overall health, impact the capacity of gut bacteria to create vitamin B12. A microbiome that is balanced and diversified is regarded to be more favorable to B12 production. Consumption of specific fibers and prebiotics, for example, may impact the proliferation and activity of B12-producing bacteria in the gut.

Final thoughts

The link between gut bacteria and vitamin B12 synthesis adds another dimension to our understanding of the microbiome’s role in human health. Gut bacteria are essential for supporting host health. Gut flora dysbiosis (imbalance between good and bad bacteria) can result in a variety of disorders. 
Relying solely on gut flora for vitamin B12 may be insufficient, especially for individuals with severe dietary limitations. Vegans and Vegetarians must investigate other sources of vitamin B12, such as fortified meals or pills. Regular health checks and blood testing can aid in determining B12 levels and addressing any inadequacies.


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