Low Protein Intake in the Population: Low Risk of Kidney Function Decline but High Risk of Mortality

Objective This population-based study investigated low protein intake, mortality, and kidney function decline. Design Observational longitudinal cohort study. Subjects Target cohort consisted of 4,679 adults participating in 1988–1992 and 2001–2007 examinations of the Gubbio Study (baseline and follow-up). Data collection included overnight urine urea nitrogen (UUN) and other variables at baseline, serum creatinine at baseline and follow-up, and mortality from baseline to follow-up. Three hundred seventy-two persons were excluded for missing data. UUN in the lowest 20% of the distribution was defined as low and used as index of low protein intake. Estimated glomerular filtration rate (eGFR, mL/minute × 1.73 m 2 ) was used as kidney function index. Intervention None (observational study). Main Outcome Measure Mortality and eGFR decline are the main outcome measures, and eGFR decline was defined as eGFR change from baseline to follow-up ≤ mean−1 standard deviation (Z-score ≤ −1). Results Eight hundred seventy-one deaths occurred over 15.9 ± 4.0 years of observation (417 from cardiovascular disease and 276 from neoplastic disease). Low UUN associated with mortality (hazard ratio, HR=1.31, 95% confidence interval, CI=1.12/1.53) due to association with mortality from neoplastic disease (HR = 1.33, 95% CI=1.02/1.76). Mortality-corrected follow-up response rate was 79.9% (n = 2845). Baseline to follow-up eGFR change was −9.9 ± 10.1, and eGFR decline was found in 454 examinees. Low UUN associated with eGFR decline only in subgroup with baseline eGFR P  = .024). Conclusion Low protein intake predicted higher mortality in the whole population and lower incidence of eGFR decline only in subgroup with reduced kidney function.