Periodontitis and Diabetes: Mechanistic Evidence of a Circular Relationship

The circular relationship between periodontitis and diabetes mellitus is one of the most established oral-systemic links. Uncontrolled diabetes contributes to an increased susceptibility and severity of periodontitis, while periodontitis contributes to poorer glycaemic control and greater insulin resistance. This reciprocal interaction is mediated by a network of interconnected mechanisms that extends beyond the traditional paradigm of bacteraemia and the hepatic acute phase response triggered by the systemic cytokine spillover from affected periodontal tissues. Experimental and clinical evidence indicate that dissemination of periodontal pathogens and virulence factors can directly affect the pancreas and liver, which are key organs in the pathogenesis of diabetes. Periodontal microbes and their virulence factors have been detected in the pancreas, eliciting β-cell dysfunction and apoptosis, compensatory alpha cell expansion and disruption of insulin-glucagon homeostasis. In addition to haematogenous spread, swallowed oral biofilm can promote oral-gut translocation, altering gut microbial ecology and contributing to entero-hepatic metabolic perturbations that exacerbate insulin resistance. The detection of periodontal pathogens by Toll-like receptors in peripheral tissues, including adipose tissue and the kidney, links periodontitis to adipose inflammation, dysregulated lipid metabolism and diabetic nephropathy. Similarly, other than eliciting the acute phase response, the systemic inflammatory spillover from periodontitis also dysregulates hepatic metabolism, increasing gluconeogenesis and impairing glycogenesis, thus contributing to hyperglycaemia. Beyond metabolic tissues, periodontal inflammation, mediated by pro-inflammatory mediators such as interleukin-6, can promote maladaptive myelopoiesis and the generation of hyperresponsive neutrophils and monocytes. In uncontrolled diabetes, chronic hyperglycaemia induces a similar trained, pro-inflammatory myeloid phenotype and the convergence of these processes may synergistically increase systemic inflammatory burden. The resulting pool of primed circulating innate immune cells can exacerbate periodontal tissue destruction and contribute to inflammatory injury in distant organs, thereby worsening diabetic complications. Overall, this review considers the complex mechanistic framework in which microbial dissemination, immune amplification and metabolic reprogramming collectively connect periodontitis and diabetes. While focused on the periodontitis-diabetes axis, this review also underscores the broader systemic relevance of periodontal inflammation in chronic metabolic disease and supports the inclusion of periodontal care as part of chronic disease management.