The Oral–Gut Microbiota Axis Across the Lifespan: New Insights on a Forgotten Interaction

The oral–gut microbiota axis is a relatively new field of research. Although most studies have focused separately on the oral and gut microbiota, emerging evidence has highlighted that the two microbiota are interconnected and may influence each other through various mechanisms shaping systemic health. The aim of this review is therefore to provide an overview of the interactions between oral and gut microbiota, and the influence of diet and related metabolites on this axis. Pathogenic oral bacteria, such as Porphyromonas gingivalis and Fusobacterium nucleatum, can migrate to the gut through the enteral route, particularly in individuals with weakened gastrointestinal defenses or conditions like gastroesophageal reflux disease, contributing to disorders like inflammatory bowel disease and colorectal cancer. Bile acids, altered by gut microbes, also play a significant role in modulating these microbiota interactions and inflammatory responses. Oral bacteria can also spread via the bloodstream, promoting systemic inflammation and worsening some conditions like cardiovascular disease. Translocation of microorganisms can also take place from the gut to the oral cavity through fecal–oral transmission, especially within poor sanitary conditions. Some metabolites including short-chain fatty acids, trimethylamine N-oxide, indole and its derivatives, bile acids, and lipopolysaccharides produced by both oral and gut microbes seem to play central roles in mediating oral–gut interactions. The complex interplay between oral and gut microbiota underscores their crucial role in maintaining systemic health and highlights the potential consequences of dysbiosis at both the oral and gastrointestinal level. Some dietary patterns and nutritional compounds including probiotics and prebiotics seem to exert beneficial effects both on oral and gut microbiota eubiosis. A better understanding of these microbial interactions could therefore pave the way for the prevention and management of systemic conditions, improving overall health outcomes.