Association between Albumin-to-Globulin Ratio and Periodontitis: A Cross-Sectional and Mendelian Randomisation Analysis.

PURPOSE: Periodontitis has been linked to systemic inflammation and nutrition. The albumin-to-globulin ratio (AGR) is a readily available inflammatory and nutritional index, but its relationship with periodontitis remains to be fully clarified. This study examined the association between AGR and periodontitis using the National Health and Nutrition Examination Survey (NHANES) data and Mendelian randomisation (MR). METHODS AND MATERIALS: The cross-sectional analysis included 10,094 participants from NHANES 2009-2014. Weighted multivariable logistic regression, restricted cubic splines (RCS), subgroup analyses, and threshold effect analysis were performed. Furthermore, MR analysis was conducted using genetic data for AGR (98,626 individuals) and periodontitis (9,560 cases and 169,166 controls) to further evaluate the relationship. RESULTS: After fully adjusting for confounders, logistic regression shows elevated AGR was associated with lower odds of periodontitis (OR = 0.52, 95% CI: 0.40-0.67). The top quartile group had 44% fewer cases of periodontitis than the lowest quartile group (OR = 0.56, 95% CI: 0.46-0.68). The RCS revealed an L-shaped nonlinear association between AGR and periodontitis. Threshold effect analysis showed that when AGR 1.79, higher AGR was significantly associated with lower odds of periodontitis (OR = 0.37, 95% CI: 0.28-0.50). Stratified analyses suggested a stronger association among participants aged 60 years. MR did not substantiate a genetic correlation between AGR and periodontitis (p = 0.304). CONCLUSION: Higher AGR was associated with a lower prevalence of periodontitis, particularly among adults aged 60 years. However, MR analysis did not provide genetic evidence supporting this link. Prospective studies are needed to clarify this relationship.