Effect of <scp>EGCG</scp> Intake on Kidney Function Chronic Kidney Disease: A Nonlinear Dose–Response Relationship and Health Impact Evidence From <scp>US</scp> Adults

Epigallocatechin gallate (EGCG), a major catechin in tea, has been linked to various health outcomes; however, its association with kidney function remains unclear. This cross-sectional study included 5001 participants from the 2009-2018 National Health and Nutrition Examination Survey (NHANES). Daily EGCG intake was estimated from two 24-h dietary recalls. Kidney function outcomes included chronic kidney disease (CKD), estimated glomerular filtration rate (eGFR), and urinary albumin-to-creatinine ratio (UACR). Multivariable logistic and linear regression models were used to assess associations, and restricted cubic spline (RCS) models were applied to examine potential nonlinear relationships. Per 100 mg/day higher EGCG, CKD odds did not change meaningfully: crude OR 1.03 (95% CI 0.93-1.15; <i>p</i> = 0.59) and adjusted OR 1.09 (0.97-1.23; <i>p</i> = 0.14). By contrast, EGCG was inversely related to eGFR: crude β -1.01 mL/min/1.73 m² (95% CI -1.59 to -0.43; <i>p</i> = 0.0006) and adjusted <i>β</i> -0.86 (-1.23 to -0.49; <i>p</i> < 0.001). UACR showed no significant associations: crude <i>β</i> -13.09 (95% CI -89.26 to 63.08; <i>p</i> = 0.736) and adjusted <i>β</i> -22.49 (-103.87 to 58.90; <i>p</i> = 0.588). RCS indicated a nonlinear association for CKD (<i>p</i>-overall = 0.021; <i>p</i>-nonlinear = 0.010) with an inflection near 48.750 mg/day; for eGFR, the overall association was significant (<i>p</i>-overall < 0.001) with a visually N-shaped curve and a turning point near 52.707 mg/day, though nonlinearity was not significant (<i>p</i>-nonlinear = 0.063). No overall or nonlinear relationships were observed for UACR (<i>p</i>-overall = 0.764; <i>p</i>-nonlinear = 0.752). Higher EGCG intake was consistently associated with lower eGFR, and a significant nonlinear association with CKD risk was identified, suggesting that the relationship between EGCG and kidney function may vary across intake levels. No association was observed with UACR.