J-shaped association between systemic immune-inflammation index and periodontitis: Results from NHANES 2009-2014

To examine the relationship between the systemic immune-inflammation index (SII) and periodontitis and to investigate possible effect modifiers.

Data used in the present cross-sectional study are from the National Health and Nutrition Examination Survey (NHANES) 2009-2014 (N = 10,301). The SII was calculated using the following formula: (neutrophils count × platelet count)/lymphocytes count. The category of periodontitis was defined by the Centers for Disease Control and Prevention and American Academy of Periodontology (CDC/AAP) classification. We employed natural cubic spline and multivariable logistic regression analyses to evaluate the associations of the SII with periodontitis.

The associations between SII and periodontal health followed a J-shape (p < 0.001). The risk of periodontitis tended to reduce with the increment of log₂(SII) in participants with log₂(SII) ≤ 8.66 (odds radio [OR] = 0.83; 95% CI: 0.69-0.999), especially among non-Hispanic Whites (OR = 0.70; 95% CI: 0.52-0.95), and increased with the increment of log₂(SII) in participants with log₂(SII) > 8.66 (OR = 1.19; 95% CI: 1.02-1.38). A similar trend was also observed between the SII and the number of sites with probing pocket depth (PPD) ≥4 mm and clinical attachment loss (CAL) ≥ 3 or 5 mm. Furthermore, we found a significantly stronger correlation between lymphocytes and either neutrophils or platelets in individuals with log₂(SII) > 8.66, as opposed to those with log₂(SII) ≤ 8.66.

There is a J-shaped association between SII and periodontitis in US adults, with an inflection point of log₂(SII) at 8.66, which may provide potential adjunctive treatment strategies for periodontitis with different immune response states. Further prospective trials are still required to confirm our findings.