Association between triglyceride glucose-body roundness index and incidence diabetes mellitus: a cohort study

Diabetes mellitus (DM) is a major global health burden. Insulin resistance (IR) is a key driver, but its direct assessment is often impractical in large-scale settings. The triglyceride-glucose (TyG) index and body roundness index (BRI) have emerged as accessible markers for IR and obesity, respectively. However, their combined role in predicting DM incidence remains unclear. This study aimed to evaluate the relationship between the TyG-BRI and DM risk, to provide a practical tool for early identification of high-risk individuals. This study included 15,310 Japanese adults who participated in the NAGALA Physical Examination Project from 2004 to 2015. To assess the association of TyG-BRI with DM incidence, Cox proportional-hazards regression model, restricted cubic spline (RCS) regression analyses, subgroup analyses, and sensitivity analyses were utilized. Time-dependent receiver operating characteristic (ROC) curve analysis was used to assess the ability of TyG-BRI to predict DM. To investigate the relationship between combined exposure to each component of TyG-BRI and DM incidence, weighted quantile sum regression analysis was employed. During the median 5.4-year follow-up duration, 350 (2.3%) participants developed DM. With TyG-BRI as a continuous variable, the HR (95% CI) for DM incidence was 1.38 (1.19-1.61) in the fully adjusted model. Participants with the highest TyG-BRI quartiles exhibited a 98% (HR 1.98, 95% CI 1.10-3.57) increased risk of DM compared to those with the lowest quartiles. RCS analysis indicated a positive linear relationship between TyG-BRI and DM incidence ( p for overall<0.001; p for nonlinear=0.465). FPG emerged as the primary contributor when the weights were assigned to the constituent elements of the TyG-BRI (weight=0.751). Time-dependent ROC analyses suggested that TyG-BRI demonstrated superior and more stable predictive capacity for incident DM compared with the TyG index and BRI over mid- to long-term follow-up. The TyG-BRI was positively associated with the risk of DM, demonstrating a dose-response relationship. Maintaining lower TyG-BRI levels may be beneficial to reduce the burden of DM.