title: Population-based dose-response curve of glomerular filtration rate to dietary protein intake.
abstract: BACKGROUND
  Kidney function measured as estimated glomerular filtration rate (eGFR) is a risk factor for mortality and severe diseases. Protein intake up-regulates kidney function. The dose-response curve of eGFR over protein intake is unknown. Urinary urea nitrogen is an objective index of protein intake.
  
  
  METHODS
  The study cross-sectionally analysed the relation between overnight urinary urea nitrogen ((on)U-ureaN) and eGFR with and without control for other variables in 4106 adults of the Gubbio population. Analyses were done for serum creatinine (S-cr) also to investigate the independency of results from eGFR calculation.
  
  
  RESULTS
  Higher (on)U-ureaN associated with higher eGFR, and lower S-cr independently of sex and age (simple and partial correlation coefficients >0.100, P < 0.001). Analyses by (on)U-ureaN decile indicated sigmoid curves of eGFR and S-cr over (on)U-ureaN with trend to flatness in the lowest 20% and the highest 20% of (on)U-ureaN (<5.19 and >10.12 mg/h, respectively). Multi-variable spline regression indicated that the relation of eGFR over (on)U-ureaN was non-significant for (on)U-ureaN <5.19 mg/h (coefficient = +0.27, 95% CI = -0.31/+0.84, P = 0.364), positive for (on)U-ureaN in the range 5.19-10.12 mg/h (coefficients = 1.35-1.64, lower 95% CI ≥ +0.48, P ≤ 0.002), and non-significant for (on)U-ureaN >10.12 mg/h (coefficient = +0.05, 95% CI = -0.06/ +0.16, P = 0.394). eGFR differed by ≈8 mL/min × 1.73 m(2) between the lowest and highest 20% of (on)U-ureaN distribution.
  
  
  CONCLUSIONS
  Higher protein intake relates to higher eGFR. The relation is sigmoid with eGFR up-regulation for (on)U-ureaN >5.19 mg/h, a threshold approximately corresponding to the recommended daily allowance for protein intake (0.8 g/day per kg of ideal weight).
authors: Department of Medicine and Surgery, University of Salerno, Baronissi, Italy.
authors: Massimo
authors: M
authors: Cirillo
authors: Department of Medicine and Surgery, University of Salerno, Baronissi, Italy.
authors: Fabiana
authors: F
authors: Zingone
authors: Department of Maternity and Pediatrics, Hospital of Benevento, Benevento, Italy.
authors: Cinzia
authors: C
authors: Lombardi
authors: Department of Physics, University of Salerno, Baronissi, Italy.
authors: Pierpaolo
authors: P
authors: Cavallo
authors: Istituto Auxologico Italiano, University of Milan, Milan, Italy.
authors: Alberto
authors: A
authors: Zanchetti
authors: Department of Medicine and Surgery, University of Salerno, Baronissi, Italy.
authors: Giancarlo
authors: G
authors: Bilancio
mesh_terms: D000328:Adult; D000368:Aged; D015331:Cohort Studies; D003404:Creatinine / Q000097:blood*; D003430:Cross-Sectional Studies; D004044:Dietary Proteins / Q000008:administration & dosage* / Q000378:metabolism*; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D007668:Kidney / Q000503:physiopathology*; D007677:Kidney Function Tests; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D012307:Risk Factors; D014508:Urea / Q000652:urine*
chemical_list: D004044:Dietary Proteins; D014508:Urea; D003404:Creatinine
keywords: creatinine; dietary protein; eGFR; kidney function; urea