Threshold effects between caffeine intake and urine flow rate: a population-based cross-sectional study

Purpose: The potential benefits of caffeine intake are currently receiving much attention and exploration. Urine flow rate (UFR) is an objective index to comprehensively reflect bladder function. The aim of this study was to investigate the association between caffeine intake and UFR using the National Health and Nutrition Examination Survey (NHANES) database. Methods: 14,142 participants were enrolled in this study. Weighted multivariate adjusted regression models were used to explore the relationship between caffeine intake and UFR. The dose–response relationships were explored using a restricted cubic spline (RCS) and a threshold effect analysis was conducted based on the inflection points identified by the two-segment linear regression model. In addition, subgroup analysis and sensitivity analysis were applied. Results: The findings suggested that the intake of caffeine was correlated with improved UFR [Model 3: 0.091 (0.057, 0.126), P value < 0.001]. In addition, the RCS supported a nonlinear relationship between them. The analysis of threshold effect further revealed a specific level of caffeine intake (34.51 mg/day) that exhibited a significant enhancement in UFR. Finally, through re-analyzing the data set obtained after multiple imputation (MI), we obtained similar results. Conclusion: This study found a nonlinear beneficial relationship between caffeine intake and UFR, and revealed the recommended intake of caffeine. The values varied by gender, race, education, and smoking status.