Sodium intake and kidney function in the general population: an observational, population-based study

Abstract

Abstract Background The relationships of sodium intake to kidney function within the population have been poorly investigated and are the objective of the study. Methods This observational, population-based, cross-sectional and longitudinal study targeted 4595 adult participants of the Gubbio study with complete data at baseline exam. Of these participants, 3016 participated in the 15-year follow-up (mortality-corrected response rate 78.4%). Baseline measures included sodium:creatinine ratio in timed overnight urine collection, used as an index of sodium intake, together with serum creatinine, sex, age and other variables. Follow-up measures included serum creatinine and other variables. Estimated glomerular filtration rate (eGFR, mL/min/1.73 m2) was calculated using serum creatinine, sex and age and was taken as an index of kidney function. Results The study cohort was stratified in sex- and age-controlled quintiles of baseline urine sodium:creatinine ratio. A higher quintile associated with higher baseline eGFR (P < 0.001). In multivariable analysis, the odds ratio (OR) of Stage1 kidney function (eGFR ≥90 mL/min/1.73 m2) was 1.98 times higher in Quintile 5 compared with Quintile 1 [95% confidence interval (CI) 1.50–2.59, P < 0.001]. The time from baseline to follow-up was 14.1 ± 2.5 years. Baseline to follow-up, the eGFR change was more negative along quintiles (P < 0.001). In multivariable analysis, the OR in Quintile 5 compared with Quintile 1 was 2.21 for eGFR decline ≥30% (1.18–4.13, P = 0.001) and 1.38 for worsened stage of kidney function (1.05–1.82, P = 0.006). Findings were consistent within subgroups. Conclusions Within the general population, an index of higher sodium intake associated cross-sectionally with higher kidney function but longitudinally with greater kidney function decline.