Baseline and longitudinal changes of body roundness index and incident type 2 diabetes: evidence from the UK Biobank cohort.

Introduction: Type 2 diabetes (T2D) is closely associated with excess adiposity, particularly visceral fat. The body roundness index (BRI), calculated from height and waist circumference, provides a refined estimate of visceral adiposity. This study aimed to investigate the associations of baseline BRI and longitudinal changes in BRI with the risk of incident T2D.

Research design and methods: We used UK Biobank data, a cohort involving adults aged 37-73 years. Both baseline and last follow-up BRI values were classified according to the tertiles of baseline BRI, and long-term BRI changes were categorized by baseline and follow-up grades. The annual average rate of change (AARC) of BRI was also calculated. Cox regression models were employed to evaluate HRs and 95% CIs, while restricted cubic splines explored non-linear relationships.

Results: Among 485 509 participants, 32 956 developed T2D during the follow-up period. Elevated baseline BRI was correlated with a greater risk of T2D, with adjusted HRs of 2.39 (95% CI: 2.28 to 2.51) and 6.23 (95% CI: 5.96 to 6.50) for the second and third tertiles of BRI, respectively. In the longitudinal analysis of 65 684 participants (1153 T2D cases), low baseline BRI with grade increase was linked to higher risk of T2D (HR: 1.49, 95% CI: 1.05 to 2.13). Among participants with middle baseline BRI, grade decrease and increase showed HRs of 0.65 (95% CI: 0.45 to 0.93) and 1.66 (95% CI: 1.32 to 2.10) versus stable middle. Grade decrease with high baseline BRI was associated with lower T2D risk (HR: 0.50, 95% CI: 0.40 to 0.62) compared with stable high. Non-linear associations between AARC of BRI and T2D risk were identified (p <0.05).

Conclusions: This study shows that both baseline BRI and long-term BRI changes are linked to T2D risk, emphasizing the significance of monitoring BRI trends for T2D prevention and control.