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 = 0.163, P < .001), lower urine osmolality (beta = 0.184, P < .001), lower eGFR (beta = 0.030, P = .002), and higher prevalence of decreased eGFR (logistic coefficient ± standard error = 1.13 ± 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.

Urinary Potassium and Kidney Function Decline in the Population-Observational Study.

Background-Some data suggest favorable effects of a high potassium intake on kidney function. The present population-based study investigated cross-sectional and longitudinal relations of urinary potassium with kidney function. Methods-Study cohort included 2027 Gubbio Study examinees (56.9% women) with age ≥ 18 years at exam-1 and with complete data on selected variables at exam-1 (1983-1985), exam-2 (1989-1992), and exam-3 (2001-2007). Urinary potassium as urinary potassium/creatinine ratio was measured in daytime spot samples at exam-1 and in overnight timed collections at exam-2. Estimated glomerular filtration rate (eGFR) was measured at all exams. Covariates in analyses included demographics, anthropometry, blood pressure, drug treatments, diabetes, smoking, alcohol intake, and urinary markers of dietary sodium and protein. Results-In multivariable regression, urinary potassium/creatinine ratio cross-sectionally related to eGFR neither at exam-1 (standardized coefficient and 95%CI = 0.020 and -0.059/0.019) nor at exam-2 (0.024 and -0.013/0.056). Exam-1 urinary potassium/creatinine ratio related to eGFR change from exam-1 to exam-2 (0.051 and 0.018/0.084). Exam-2 urinary potassium/creatinine ratio related to eGFR change from exam-2 to exam-3 (0.048 and 0.005/0.091). Mean of urinary potassium/creatinine ratio at exam-1 and exam-2 related to eGFR change from exam-1 to exam-3 (0.056 and 0.027/0.087) and to incidence of eGFR < 60 mL/min per 1.73 m2 from exam-1 to exam-3 (odds ratio and 95%CI = 0.78 and 0.61/0.98). Conclusion-In the population, urinary potassium did not relate cross-sectionally to eGFR but related to eGFR decline over time. Data support the existence of favorable effects of potassium intake on ageing-associated decline in kidney function.

Sodium Intake and Proteinuria/Albuminuria in the Population-Observational, Cross-Sectional Study.

Sodium effects on proteinuria are debated. This observational, cross-sectional, population-based study investigated relationships to proteinuria and albuminuria of sodium intake assessed as urinary sodium/creatinine ratio (NaCR). In 482 men and 454 women aged 35-94 years from the Moli-sani study, data were collected for the following: urinary NaCR (independent variable); urinary total proteins/creatinine ratio (PCR, mg/g), urinary albumin/creatinine ratio (ACR, mg/g), and urinary non-albumin-proteins/creatinine ratio (calculated as PCR minus ACR) (dependent variables). High values were defined as PCR ≥ 150 mg/g, ACR ≥ 30 mg/g, and urinary non-albumin-proteins/creatinine ratio ≥ 120 mg/g. Urinary variables were measured in first-void morning urine. Skewed variables were log-transformed in analyses. The covariates list included sex, age, energy intake, body mass index, waist/hip ratio, estimated urinary creatinine excretion, smoking, systolic pressure, diastolic pressure, diabetes, history of cardiovascular disease, reported treatment with antihypertensive drug, inhibitor or blocker of the renin-angiotensin system, diuretic, and log-transformed data of total physical activity, leisure physical activity, alcohol intake, and urinary ratios of urea nitrogen, potassium, and phosphorus to creatinine. In multivariable linear regression, standardized beta coefficients of urinary NaCR were positive with PCR (women and men = 0.280 and 0.242, 95% confidence interval = 0.17/0.39 and 0.13/0.35, p < 0.001), ACR (0.310 and 0.265, 0.20/0.42 and 0.16/0.38, p < 0.001), and urinary non-albumin-proteins/creatinine ratio (0.247 and 0.209, 0.14/0.36 and 0.09/0.33, p < 0.001). In multivariable logistic regression, higher quintile of urinary NaCR associated with odds ratio of 1.81 for high PCR (1.55/2.12, p < 0.001), 0.51 of 1.62 for high ACR (1.35/1.95, p < 0.001), and of 1.84 for high urinary non-albumin proteins/creatinine ratio (1.58/2.16, p < 0.001). Findings were consistent in subgroups. Data indicate independent positive associations of an index of sodium intake with proteinuria and albuminuria in the population.