To explore the relationship between body roundness index (BRI) and new onset arthritis, and provide a new perspective for the prevention and treatment of arthritis.

A cohort study design was adopted, using the data of 2011 and 2020 in the China longitudinal study on the China Health and Retirement Longitudinal Study (CHARLS), taking BRI as the exposure factor, high-density lipoprotein cholesterol (HDL-C), total cholesterol, triglycerides, low-density lipoprotein cholesterol (LDL-C) as the intermediary variables, including demographic characteristics such as age and gender, smoking, alcohol consumption and other health behaviors as confounding factors, and new onset arthritis as the outcome. Statistical analysis was carried out using multiple model logistic regression strategy, restricted cubic spline, subgroup analysis and intermediary analysis. Compared with relevant studies, the main purpose of the dose-response relationship we explored is to study whether there is a nonlinear relationship between exposure and outcome, that is, whether the risk of outcome will change accordingly with the change of exposure level.

A total of 5 166 participants were included, and BRI was positively correlated with arthritis, with an OR value of 1.196 (95% CI: 1.047-1.367). The prevalence of new onset arthritis increased by 19.6% when BRI increased by a quartile range; The dose-response relationship showed that BRI > 3.943 was positively correlated with the incidence of arthritis; Subgroup analysis showed that the positive correlation between BRI and new onset arthritis was not affected by many factors; Mediation analysis showed that HDL-C had a protective effect on arthritis, mediating about 6.84% of the impact of BRI on the incidence of arthritis. The mediation effect of total cholesterol, triglycerides and LDL-C was not significant; The AUC of BRI for predicting new onset arthritis (0.546) was higher than that of BMI (0.527).

The increased level of BRI may lead to an increased risk of arthritis, and HDL-C may alleviate this risk. In the future, its clinical application potential and regulatory strategies should be explored to reduce the incidence of arthritis and improve the prognosis.