Abstract
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.
Highlights
Glomerular filtration rate and proteinuria or albuminuria are essential components for the diagnosis and for the staging of chronic kidney disease [1]
The mode was in the intermediate values for urinary NaCR and in the lowest tail for PCR, ACR, and urinary non-albumin proteins to creatinine ratio
The results are in contrast to the conclusions of the study of Sharma et al, where sodium intake was assessed by dietary recalls [37], a method that is notoriously affected by various biases [15]
Summary
Glomerular filtration rate and proteinuria or albuminuria are essential components for the diagnosis and for the staging of chronic kidney disease [1]. There is not agreement on the possibility that a sodium intake restriction per se might favor the prevention and/or the control of proteinuria or albuminuria [2]. Intervention studies reported favorable effects of sodium restriction but could not dissociate the effects on blood pressure from those on albuminuria or proteinuria [2,3,4]. The present study was designed to analyze in a sample of the general population the associations of urinary sodium, taken as index of sodium intake, with proteinuria, albuminuria, and urinary non-albumin proteins, separately. The analyses were controlled for many confounders including socio-cultural factors, anthropometry, blood pressure status, kidney function, lifestyle, and dietary and biochemical markers
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