The association between the body roundness index and the risk of rheumatoid arthritis: a cross-sectional study based on NHANES

Objective: There is increasing evidence of an association between rheumatoid arthritis (RA) and obesity. However, the precise relationship between BRI, a novel indicator of visceral fat, and RA remains unclear. The objective of this study was to investigate the relationship between BRI and RA risk. Methods: A cross-sectional study was conducted using data from the NHANES from 2011 to 2020. A logistic regression analysis was employed to investigate the correlation between the BRI and RA risk, and restricted cubic splines (RCS) and fitting curve analysis were used to capture the potential non-linear relationship. Furthermore, a piecewise two-stage logistic regression model combined with smoothing techniques was employed to explore the potential threshold effect of BRI on RA risk. Results: A total of 6.25% (830/13,273) of the 13,273 participants aged 20 and above included in the study were diagnosed with RA. The adjusted OR values for BRI and RA in Q2 (3.666, 4.924), Q3 (4.924, 6.477), and Q4 (6.470, 20.970) were compared with those for individuals with lower BRI-Q1 (1.049, 3.666). The ORs for the remaining categories were 1.22 (95% CI: 0.91–1.64, p = 0.181), 1.64 (95% CI: 1.25–2.17, p < 0.001) and 2.04 (95% CI: 1.55–2.70, p < 0.001), respectively. The results of the trend analysis showed that the adjusted OR for the trend was 1.28 (95% CI: 1.18–1.38, P < 0.001). The results of the RCS analysis indicated a significant linear correlation between the risk of RA and increasing BRI ( p -value for the overall <0.001, p -value for non-linearity = 0.627). A sensitivity analysis demonstrated that when BRI was treated as a continuous variable, the observed association remained, with an adjusted OR of 1.12 (95% confidence interval: 1.08-1.15, P < 0.001). Subgroup analysis indicated that BRI interacted with smoking status, age and marital status, with never smokers, those under 50 and those living with a partner being more susceptible to BRI. Conclusions: A significant positive correlation was observed between the risk of RA and BRI, particularly in individuals who had never smoked, were under the age of 50, and living with a partner. It is proposed that maintaining an appropriate BRI may contribute to a reduction in the incidence of RA.