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.