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

Long-term association between water intake and kidney function in a population at high cardiovascular risk

OBJECTIVES

The evidence on water intake in the prevention of kidney function decline is scarce at population level in well-being individuals at high cardiovascular risk. Therefore, we aimed to longitudinally evaluate the associations between total water intake and subtypes and kidney function, through estimated-Glomerular Filtration Rate (eGFR).

METHODS

Three-year prospective analysis conducted in 1986 older adults (aged 55-75 year) with overweight/obesity and metabolic syndrome from the PREDIMED-Plus study. Water intake was assessed using validated beverage and food frequency questionnaires. Serum creatinine-based eGFR (SCr-based eGFR; ml/min/1.73 m2) was estimated using the CKD-EPI equation at baseline, one-year and 3-years of follow-up. Mixed-effects linear regression models were fitted to evaluate the associations between baseline total water intake and subtypes, and SCr-based eGFR over 3-years of follow-up.

RESULTS

Participants in the highest baseline tertile of total water intake, plain water and water from all fluids showed a lower decrease in SCr-based eGFR after 3-years of follow-up, compared to those in the lowest tertile. Participants with the highest tap water consumption showed a lower SCr-based eGFR decline after 1-year and 3-years of follow-up, in comparerd to participants in the lowest intake category (T3 vs. T1: β: 1.4 ml/min/1.73 m2; 95%CI: 0.5-2.3, β: 1.0; 95%CI: 0.1-2.0, respectively).

CONCLUSIONS

Plain water rather than other water sources, and especially tap water, was associated with lower kidney function decline assessed through eGFR over 3-years of follow-up, in older individuals at high cardiovascular risk.

TRIAL REGISTRATION

ISRCTN89898870. Retrospectively registered on 24 July 2014.

Relation of Alcohol Intake to Kidney Function and Mortality Observational, Population-Based, Cohort Study

Data are conflicting about the effects of alcohol intake on kidney function. This population-based study investigated associations of alcohol intake with kidney function and mortality. The study cohort included adult participants in Exam-1, Exam-2 (6-year follow-up), and Exam-3 (20-year follow-up) of the Gubbio study. Kidney function was evaluated as estimated glomerular filtration rate (eGFR, CKD-Epi equation, mL/min × 1.73 m2). Daily habitual alcohol intake was assessed by questionnaires. Wine intake accounted for >94% of total alcohol intake at all exams. Alcohol intake significantly tracked over time (R > 0.66, p < 0.001). Alcohol intake distribution was skewed at all exams (skewness > 2) and was divided into four strata for analyses (g/day = 0, 1−24, 25−48, and >48). Strata of alcohol intake differed substantially for lab markers of alcohol intake (p < 0.001). In multivariable regression, strata of alcohol intake related cross-sectionally to eGFR at all exams (Exam-1: B = 1.70, p < 0.001; Exam-2: B = 1.03, p < 0.001; Exam-3: B = 0.55, p = 0.010) and related longitudinally to less negative eGFR change from Exam-1 to Exam-2 (B = 0.133, p = 0.002) and from Exam-2 to Exam-3 (B = 0.065, p = 0.004). In multivariable Cox models, compared to no intake, intakes > 24 g/day were not associated with different mortality while an intake of 1−24 g/day was associated with lower mortality in the whole cohort (HR = 0.77, p = 0.003) and in the subgroup with eGFR < 60 mL/min × 1.73 m2 (HR = 0.69, p = 0.033). These data indicate a positive independent association of alcohol intake with kidney function not due to a mortality-related selection.

Causal Association Between Tea Consumption and Kidney Function: A Mendelian Randomization Study

Background

Causal research concerning the consumption of tea and the risk of chronic kidney disease (CKD) is limited. This study identified the potential causal effects of tea intake on CKD, the estimated glomerular filtration rate (eGFR), and albuminuria.

Methods

Genome-wide association studies (GWASs) from UK Biobank were able to identify single-nucleotide polymorphisms (SNPs) associated with an extra cup of tea each day. The summary statistics for the kidney function from the CKDGen consortium include 11,765 participants (12,385 cases of CKD) and 54,116 participants for the urinary albumin-to-creatinine ratio who were mostly of European descent. A two-sample Mendelian randomization (MR) analysis was performed to test the relationship between the selected SNPs and the risk of CKD.

Results

A total of 2,672 SNPs associated with tea consumption (p < 5 × 10^-8) were found, 45 of which were independent and usable in CKDGen. Drinking more cups of tea per day indicates a protective effect for CKD G3-G5 [odds ratio (OR) = 0.803; p = 0.004] and increases eGFR (β = 0.019 log ml/min/1.73 m² per cup per day; p = 2.21 × 10^-5). Excluding two SNPs responsible for directional heterogeneity (Cochran Q p = 0.02), a high consumption of tea was also negatively correlated with a lower risk of albuminuria (OR = 0.758; p = 0.002).

Conclusion

From the perspective of genes, causal relationships exist between daily extra cup of tea and the reduced risk of CKD and albuminuria and increased eGFR.

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.