The Oral Microbiome and Systemic Health: Current Insights into the Mouth–Body Connection

The oral cavity contains a complex and dynamic microbial ecosystem that plays a central role in maintaining both local and systemic homeostasis. Emerging evidence indicates that disturbances in oral microbial communities-including genetic and functional diversity within species-are associated not only with oral diseases but may also contribute to the development and progression of systemic diseases. This narrative review summarises the current state of knowledge on bidirectional interactions between oral microbial communities and major organ systems. A comprehensive search of PubMed/MEDLINE, Web of Science, Scopus, and Cochrane databases was conducted for studies published between 2019 and 2025, prioritising systematic reviews, meta-analyses, and high-quality mechanistic studies. Ultimately, 40 articles were included in the narrative synthesis. The results provide clear evidence of an association between oral dysbiosis and cardiovascular disease (CVD), type 2 diabetes mellitus (T2DM), chronic respiratory infections, and adverse pregnancy outcomes (APOs). Recent data also suggest links with neurodegenerative disorders, chronic kidney disease (CKD), autoimmune diseases, and cancer. Proposed mechanisms include transient or persistent bacteraemia, systemic inflammation caused by microbial metabolites and endotoxins, disruption of immune homeostasis, molecular mimicry, and modulation of host metabolic pathways. Despite growing evidence linking oral microbial communities to systemic health, most findings are based on observational studies, and causal relationships remain to be established through longitudinal and interventional research. Understanding the connection between the mouth and the body highlights the potential for targeting oral microbial activity, virulence factors, and host inflammatory responses in disease prevention and treatment.