Blood urea nitrogen to creatinine ratio is associated with physical frailty in older-aged Chinese: a cross-sectional study

The relationship between the ratio of blood urea nitrogen to creatinine (BUN/Cr) and physical frailty in elderly patients remains unclear. The study aims to investigate the association between the BUN/Cr ratio and physical frailty in the elderly Chinese population. In this cross-sectional analysis, the clinical data of 5213 participants from 2015 were selected from the China Health and Retirement Longitudinal Study (CHARLS). The demographic variables (including age and gender) and health behavior (including smoking and drinking history), anthropometric (including systolic and diastolic blood pressure, waist circumference (WC), etc.), physical performances (i.e., grip strength, repeated chair stands, etc.), and biochemical indicators (i.e., blood urea nitrogen (BUN), creatinine(Cr), total cholesterol (TC), triglycerides (TG), etc.) were measured. The association between the BUN/Cr ratio and physical frailty was analyzed. After adjusting for potential confounding factors, smooth curve fitting showed a linear relationship between the BUN/Cr ratio and grip strength, a non-linear relationship between the BUN/Cr ratio, and repeated chair-rising time. The fully adjusted linear regression results showed a negative association between the BUN/Cr ratio and grip strength. In the multivariate, piecewise linear regression, when the BUN/Cr ratio was greater than 18.60, the repeated chair-rising time increased with the increase in BUN/Cr ratio (β = 0.046, 95%CI 0.025, 0.066; p < 0.001). However, we did not observe a significant correlation when the BUN/Cr ratio was less than 18.60 (β = −0.007, 95%CI −0.046, 0.032; p = 0.717). This study demonstrated that the BUN/Cr ratio might be associated with physical frailty in older-aged Chinese, and this association requires further investigation.