Shared oral microbiome signatures linking periodontitis and autoimmune thyroiditis: NHANES 2009-2012.

OBJECTIVE: To examine the association between periodontitis severity and autoimmune thyroiditis (AIT) in a nationally representative US sample and to explore oral microbiome features shared between the two conditions. METHODS: We analyzed adults from NHANES 2009-2012 with complete periodontal examinations, thyroid autoantibodies, and oral microbiome data (n = 1,346). Periodontitis was classified using CDC/AAP case definitions. AIT was defined as positivity for thyroid peroxidase antibodies (TPOAb ≥ 9 IU/mL) and/or thyroglobulin antibodies (TgAb ≥ 4 IU/mL). Survey-weighted multivariable logistic regression estimated adjusted odds ratios (aORs) and 95% confidence intervals (CIs). Oral microbiome diversity and differentially abundant genera were compared between groups. RESULTS: In the fully adjusted model, mild and severe periodontitis were associated with higher odds of AIT compared with periodontally healthy individuals (mild: aOR 2.15, 95% CI 1.20-3.84; severe: aOR 2.77, 95% CI 1.22-6.28), whereas moderate periodontitis was not significantly associated (aOR 1.47, 95% CI 0.63-3.43). Genera enriched in both AIT and periodontitis included Fusobacterium, Bergeyella, Johnsonella, and Prevotella_2. Fusobacterium abundance increased across periodontal severity categories and showed a weak inverse correlation with TPOAb, whereas TT3 and FT3 showed weak positive correlations with Fusobacterium. CONCLUSION: Periodontitis severity was associated with AIT in this cross-sectional NHANES analysis, and Fusobacterium emerged as a shared genus associated with both periodontal status and thyroid autoimmunity. Longitudinal and interventional studies are warranted to assess causality.