Association Between Baseline Blood Urea Nitrogen-to-Creatinine Ratio and Incident Sarcopenia in Middle-Aged and Older Chinese Adults: Findings from the CHARLS Cohort

This study aimed to comprehensively investigate the association between the Blood Urea Nitrogen-to-Creatinine Ratio and Incident Sarcopenia.We included 6,494 CHARLS (China Health and Retirement Longitudinal Study) participants aged ≥ 45 years who were free of sarcopenia at baseline (2011) and were followed prospectively until 2015.Logistic regression estimated incident sarcopenia odds ratios (ORs) with 95% confidence intervals (CIs) across BUN/Cr levels, adjusting for sociodemographic characteristics, lifestyle, and health-relevant covariates. Restricted cubic splines modeled the dose-response relationship flexibly. Subgroup analyses by age, sex, and other factors were performed. Over 4 years, 673 participants (10.4%) developed sarcopenia. These individuals were older (62.5 ± 7.9 vs 56.6 ± 7.8 years) and had higher baseline BUN/Cr ratios (22.7 ± 7.6 vs 20.7 ± 6.6) than those without sarcopenia (p < 0.001). Each interquartile range increase in BUN/Cr was associated with a 17% higher sarcopenia odds after full adjustment (OR 1.17, 95% CI 1.05–1.31, p = 0.006). Participants in the highest BUN/Cr quartile had a 57% increased risk compared to the lowest quartile (OR 1.57, 95% CI 1.22–2.03). A roughly linear exposure-response relationship was observed (p = 0.013), with consistent associations across all subgroups. Prospectively, elevated baseline BUN/Cr independently predicted 4-year incident sarcopenia in this nationally representative cohort.