Relationship of the Intake of Water and Other Beverages With Renal Endpoints: Cross-Sectional and Longitudinal Data — Observational, Population-Based Study

Objectives: The relationship of water intake with kidney function in the population is uncertain. This study investigated cross-sectionally and longitudinally the relationship of the intake of water and other beverages with kidney function within an adult Italian population sample. Methods: In 4,554 Gubbio Study examinees (54.4% women, age 18-95 years), data collection at baseline included demographics, anthropometry, questionnaires on habitual intakes of water and other beverages (non-water fluids), a timed overnight urine collection, estimated glomerular filtration rate (eGFR), decreased eGFR ( , 60 mL/minute/1.73 m2), and other variables including urinary markers of diet. At 15-year follow-up, the incidence of renal/kidney replacement therapy, the eGFR change from baseline, and the incidence of decreased eGFR were used as indices of kidney function change over time. Results: In multivariable analyses, higher water intake is independently related to higher urine flow (beta 5 0.163, P , .001), lower urine osmolality (beta 5 0.184, P , .001), lower eGFR (beta 5 0.030, P 5 .002), and higher prevalence of decreased eGFR (logistic coefficient 6 standard error 5 1.13 6 0.32, P , .001). Water intake did not relate to kidney function change over time. Intake of non-water fluids did not independently relate to urinary indices nor to kidney function. Conclusions: In the general population, water intake relates cross-sectionally to urine flow, urine concentration, and kidney function but it does not relate to kidney function change over time. The intake of other beverages does not relate to urinary indices or kidney function. Results do not support a role of water intake in kidney function decline over time in the population.