# Association of BRI With Psoriasis and Mediator Effect of SII: A Study Based on NHANES (2003–2006, 2009−2014)

## TL;DR

This study finds that body roundness index is linked to psoriasis, with systemic immune-inflammation index partially mediating this relationship.

## Contribution

The novel finding is that SII partially mediates the association between BRI and psoriasis prevalence.

## Key findings

- BRI shows a nonlinear association with psoriasis, with a point of inflection at 5.103.
- SII mediates 9.48% of the effect of BRI on psoriasis prevalence.
- The association between BRI and psoriasis is stronger on the left side of the inflection point.

## Abstract

The prevalence of psoriasis (Pso), a chronic immune‐mediated inflammatory skin disease, is high in patients with obesity. This study investigates the mediating role of the systemic immune‐inflammation index (SII) in the association between body roundness index (BRI) and Pso prevalence.

This study included 14,669 participants from the National Health and Nutrition Examination Survey (NHANES) (2003–2006, 2009−2014). The presence or absence of obesity was identified using the BRI, and Pso was assessed using the Pso questionnaire. The association of BRI with Pso was explored by weighted multivariate logistic regression analyses and restricted cubic spline (RCS) analyses, and the threshold effect was further examined using two‐stage linear regression models. Mediation analyses assessed SII’s role in the BRI‐Pso association. The Pso group included 445 out of 14,669 participants. Logistic regression analyses indicated a positive association between BRI and Pso after adjusting for potential confounders. RCS analyses showed a nonlinear relation between BRI and Pso (P
nonlinear = 0.018), with a point of inflection at 5.103 (odds ratio [OR] = 1.09, 95% CI: 1.04, 1.14). BRI and Pso were positively correlated on the left side of the point of inflection (OR = 1.25, 95% CI: 1.09, 1.45), whereas such an association was not detected on the right side (OR = 1.04, 95% CI: 0.97, 1.11). Mediation analysis showed SII partially mediated this association, accounting for 9.48% of the effect (p < 0.001).

BRI is positively associated with Pso, with SII playing a mediating role. These findings highlight the importance of visceral fat management and SII monitoring in addressing Pso and its metabolic comorbidities.