The Time Effect of the Impact of the Body Roundness Index on Kidney Disease: A Cluster Analysis Based on Longitudinal Data

Background Central obesity is a key modifiable risk factor for kidney disease. The Body Round-ness Index (BRI) is useful for assessing central obesity and associated metabolic risks. This study aimed to investigate the correlation between body roundness index (BRI) and the risk of kidney disease and explore the possibility of using BRI monitoring to identify high-risk groups. Methods This study used longitudinal data from the China Health and Retirement Longitudinal Study (CHARLS) including 2,160 participants. K-means clustering identified patterns in BRI changes, and logistic regression was used to assess the association between BRI and kidney disease risk. Subgroup and restricted cubic spline analyses were conducted to explore non-linear relationships and influencing factors. Results The best clustering of BRI was achieved by dividing participants into four groups. Significant differences were observed in demographic, physical, and clinical characteristics. Logistic regression revealed that groups B (P < 0.001) and C (P = 0.007) had significantly higher kidney disease risk compared to group A. No significant difference was observed for group D. Subgroup analysis showed elevated kidney disease risk in group B across all subgroups, and higher risk in women and those under 60 in group C. A non-linear, U-shaped relationship between BRI and kidney disease risk was observed, with both high and low BRI levels increasing risk. Conclusions The impact of BRI on kidney disease is time-dependent. Both persistently high and low BRI levels are risk factors, highlighting the value of BRI monitoring for early identification and prevention of high-risk populations.