Oral health and diabetes: a systematic review and meta-analysis.

BACKGROUND: Diabetes is a major public health challenge, affecting nearly 828 million people worldwide. Similarly, oral diseases such as dental caries, periodontal diseases, and oral cancers are highly prevalent, affecting approximately 3·7 billion individuals globally. Diabetes and oral diseases share common risk factors and studies suggest a potential relationship in which poor management of one potentially exacerbates the other. However, the direction, magnitude, and consistency of these associations remain unclear, and oral health remains largely overlooked in diabetes prevention and management strategies. The aim of this study is to systematically assess and synthesise the evidence on the longitudinal association between diabetes and oral diseases. METHODS: We conducted a systematic review and meta-analysis reported in accordance with PRISMA guidelines. We searched four electronic databases (Embase, PubMed, Web of Science, and LILACS) and grey literature from database inception to Oct 27, 2025. Eligible studies included longitudinal prospective studies examining associations between diabetes (type 1, type 2, or gestational) and core WHO oral diseases (periodontitis, dental caries, tooth loss or edentulism [complete tooth loss], and oral cancer). Random-effects meta-analyses were performed using the restricted maximum likelihood method to estimate pooled effect sizes with 95% CIs of hazard ratios (HRs) and risk ratio (RR). Methodological quality was assessed using the Newcastle-Ottawa Scale for cohort studies. FINDINGS: We screened 45 477 records and included 28 longitudinal studies from 16 countries, encompassing over 300 000 participants. Most studies were population-based and of moderate-to-high methodological quality. A bidirectional temporal association in incidence patterns was observed between diabetes and periodontitis. Individuals with periodontitis at baseline showed a 18-25% higher occurrence of newly incident type 2 diabetes during follow-up, and baseline diabetes status was associated with a higher newly incident cases of periodontitis, with pooled RRs indicating modest differences between groups. Tooth loss was also associated with newly incident type 2 diabetes over time (HR 1·12-1·20). Quantitative pooling was not feasible for edentulism outcomes; however, individuals who were edentulous at baseline showed a higher occurrence of newly incident type 2 diabetes (RR 1·30). Evidence regarding dental caries was scarce and heterogeneous, precluding meta-analysis. No longitudinal evidence was identified for oral cancer. INTERPRETATION: Findings from this longitudinal synthesis indicate associations between diabetes and oral diseases in both directions; however, the strength and consistency of evidence are asymmetric. Evidence suggests that people with periodontitis and edentulism are more likely to be diagnosed with type 2 diabetes than people without periodontitis and edentulism in the future. People with diabetes are more likely to be diagnosed with periodontitis than people without diabetes, but with less consistent evidence. Our findings support integrating oral health within interdisciplinary diabetes prevention and management strategies. FUNDING: WHO Oral Health Programme.