B vitamins & your Gut Microbes
B vitamins constitute a crucial group of water-soluble organic compounds vital for various physiological functions across nearly all living organisms. Acting primarily as cofactors, they play diverse functional roles within the body(1). For instance, B vitamins participate in essential cellular processes such as cellular aerobic respiration, immune functions, neurotransmitter synthesis, metabolism, cell signaling, and nucleic acid biosynthesis(2).
The gut functions as a conduit for the transit and absorption of ingested nutrients. Within the gut reside various microorganisms collectively known as the gut microbiome, encompassing dominant phyla like Bacteroidetes and Firmicutes, Actinobacteria, Proteobacteria, and Verrucomicrobia. These microorganisms maintain a symbiotic relationship with the host, offering protection against harmful pathogens, enhancing intestinal fermentation, and modulating host immune function(3). While the human gut microbiota is relatively stable, its composition undergoes dynamic remodeling throughout different stages of life, influenced by factors like birth method, age, lifestyle, medications, and notably, diet(3).
Interestingly, the gut harbors bacteria capable of producing B vitamins, though in limited quantities. Certain gut bacteria require specific vitamins for their growth, creating a competitive environment within the gut microbiota. Deficiencies in these vitamins can disrupt normal cellular metabolism, leading to the development of chronic diseases in humans. Even though they are produced by gut bacteria, B vitamins are also essential for their survival. Therefore, a dietary supply of these vitamins is crucial to meet the daily requirements of both the host and your gut microbiota. In turn, B vitamins help to shape the diversity of the microbiome.
Vitamin B1/Thiamin: Thiamin is important for glycolysis, tricarboxylic acid (TCA) cycle, and the pentose phosphate pathway. While several bacteria can synthesize free thiamine, dietary thiamine is absorbed primarily in the small intestine. While the precise impact of thiamine on intestinal integrity remains elusive, emerging evidence hints at its involvement in regulation of immune cells within the gut(4).
Vitamin B2/Riboflavin: Riboflavin participates in carbohydrate, fat, and protein metabolism5. Riboflavin is primarily produced in the large intestine, while dietary riboflavin is absorbed in the small intestine. In the gut Bacteroidetes, Fusobacteria and Proteobacteria are the primary riboflavin producers and about 50% of Firmicutes can produce riboflavin. And its supplementation increases levels of Faecalibacterium prausnitziiand Roseburia(5).
Vitamin B3/Niacin: Niacin plays a critical role as a redox cofactor in metabolic processes. Intestinal bacteria synthesize vitamin B3 primarily from amino acid tryptophan6, with various bacteria capable of producing it in the gut, such as Bacilli, Clostridia, Proteobacteria and Bacteroidetes. B3 seems to be a powerful protector of colonic cells and epithelial integrity(6).
Vitamin B5/Pantothenic Acid: Vitamin B5 participates in various metabolic pathways because it is a precursor of coenzyme A. Several bacteria, including Escherichia coli and Salmonella typhimurium, can synthesize vitamin B5(7).
Vitamin B6/Pyridoxine: Vitamin B6 acts as a cofactor in the generation of amino acids and neurotransmitters, is involved in fatty acid metabolism, and acts as an antioxidant(8,9). Bacteroides fragilis, Prevotella copri, Bifidobacterium longum, Collinsella aerofasciens, and Helicobacter pylori can synthesize B6 in the large intestine(10). However, the vitamin B6 produced in the gut is insufficient to meet the host's daily needs. Its deficiency has been found to reduce microbial diversity and significantly alter intestinal metabolites. Elevated levels of Lachnospiraceae(11) and Prevotella(12) were observed with vitamin B6 deficiency, whereas high vitamin B6 intake led to decreased abundance of Bacteroides(11,12).
Vitamin B7/Biotin: Biotin serves as a coenzyme in biochemical reactions such as glycolysis and cell signaling and gene regulation. Several gut bacteria, including Bacteroides fragilis and Prevotella copri, can produce vitamin B7 while Lactobacillus reduces B7 levels.
Vitamin B9/Folate: Every living cell requires folate to perform a variety of biochemical processes(13). For example, folate impacts cell survival and proliferation, regulates genes in immune cells, and impacts gut integrity and brain function(13). Folate is supplied through diet and by gut bacteria, such as Bacteroides fragilis and Prevotella copri, a few Lactobacillus species, Streptococcus and Bifidobacterium(2).
Vitamin B12/Cobalamin: B12 is one of the most complex vitamins and is essential for protein and lipid metabolism, regulating the central nervous system and for the synthesis of red blood cells (RBCs)8. While only 20% of the bacteria in the gut can synthesize B12 80% of the microbiota requires it(14).
Various factors can influence the synthesis of B vitamins by the gut microbiota, including exposure to antibiotics, free radicals, genetics, dietary habits and lifestyle. These factors, in turn, impact the gut microbial profile, colonic health, and overall host metabolism, emphasizing the intricate relationship between B vitamins, gut microbiota, and host health. Understanding these interactions provides insights into how dietary B vitamins affect gut-host interactions
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