Urinary sodium excretion and kidney failure in nondiabetic chronic kidney disease

Renal outcomes and dietary potassium: the overshadowed electrolyte?

Smyth et al. examined the association between urinary sodium and potassium excretion and adverse renal outcomes in adults at high cardiovascular risk. They found no association between urinary sodium excretion and adverse renal outcomes, but a reduced odds of adverse renal outcomes with higher urinary potassium excretion. This finding is quite interesting and a major advancement from this study. It will be important to ascertain whether this finding holds true in individuals free from vascular disease and diabetes, as well as in patients with chronic kidney disease.

[New insights into sodium in kidney and cardiovascular diseases]

Recent guidelines recommend a restriction of sodium intake below 2,4 g/day (6 g/day of NaCl) in general population to prevent arterial hypertension and cardiovascular disease. Three papers published in 2014 by The New England Journal of Medecine confirm the association between high sodium intake and arterial hypertension. However, marked sodium restriction is also associated with increased mortality. On the other hand, a diet rich in potassium, over 1.5 g/day, is associated with less cardiovascular mortality, and less chronic kidney disease progression.

Association between sodium intakes with the risk of chronic kidney disease: evidence from a meta-analysis

OBJECTIVE

Inconsistent results regarding the association between sodium intake and the risk of chronic kidney disease (CKD) have been reported. Thus, we conducted a meta-analysis to summarize the evidence from epidemiological studies of sodium with the risk of CKD.

METHODS

Pertinent studies were identified by searching of PubMed and Web of Science. The random effect model was used to combine the results. Meta-regression and subgroups analyses were used to explore potential sources of between-study heterogeneity. Publication bias was estimated using Egger's regression asymmetry test.

RESULTS

Finally, 9 articles involving 5638 CKD cases were included in this meta-analysis. Pooled results suggested that highest sodium intake level versus lowest level was significantly associated with the risk of CKD [summary relative risk (RR) = 1.088, 95% CI = 1.009-1.193, I(2) = 78.1%], especially among Europe [summary RR = 1.097, 95% CI = 1.009-1.205], but not in the America. The association was also found in the prospective studies [summary RR = 1.096, 95% CI = 1.007-1.192], but not in the cross-sectional studies. No evidence of significant publication bias was found.

CONCLUSIONS

Higher sodium intake might increase the risk of CKD.

Reduction in sodium intake is independently associated with improved blood pressure control in people with chronic kidney disease in primary care

Decreasing sodium intake has been associated with improvements in blood pressure (BP) and proteinuria, two important risk factors for CVD and chronic kidney disease (CKD) progression. We aimed to investigate the role of sodium intake by examining the effect of changes in sodium intake over 1 year on BP and proteinuria in people with early stage CKD. From thirty-two general practices, 1607 patients with previous estimated glomerular filtration rate of 59-30 ml/min per 1.73 m² and mean age of 72.9 (sd 9.0) years were recruited. Clinical assessment, urine and serum biochemistry testing were performed at baseline and after 1 year. Sodium intake was estimated from early morning urine specimens using an equation validated for this study population. We found that compared with people who increased their sodium intake from ≤ 100 to >100 mmol/d over 1 year, people who decreased their intake from >100 to ≤ 100 mmol/d evidenced a greater decrease in all BP variables (Δmean arterial pressure (ΔMAP) = -7.44 (SD 10.1) v. -0.23 (SD 10.4) mmHg; P<0.001) as well as in pulse wave velocity (ΔPWV = -0.47 (SD 1.3) v. 0.08 (SD 1.88) m/s; P<0.05). Albuminuria improved only in albuminuric patients who decreased their sodium intake. BP improved in people who maintained low sodium intake at both times and in those with persistent high intake, but the number of anti-hypertensive increased only in the higher sodium intake group, and PWV improved only in participants with lower sodium intake. Decreasing sodium intake was an independent determinant of ΔMAP. Although more evidence is needed, our results support the benefits of reducing and maintaining sodium intake below 100 mmol/d (2.3-2.4 g/d) in people with early stages of CKD.

Chronic kidney disease

INTRODUCTION

Continued progression of kidney disease will lead to renal function too low to sustain healthy life. In developed countries, such people will be offered renal replacement therapy in the form of dialysis or renal transplantation. Requirement for dialysis or transplantation is termed end-stage renal disease (ESRD).

METHODS AND OUTCOMES

We conducted a systematic review, aiming to answer the following clinical questions: What are the effects of a low-sodium diet to reduce progression rate of chronic kidney disease? What are the effects of a low-protein diet to reduce progression rate of chronic kidney disease? We searched: Medline, Embase, The Cochrane Library, and other important databases up to September 2014 (Clinical Evidence overviews are updated periodically; please check our website for the most up-to-date version of this overview).

RESULTS

We found seven studies that met our inclusion criteria. We performed a GRADE evaluation of the quality of evidence for interventions.

CONCLUSIONS

In this systematic overview we present information relating to the effectiveness and safety of the following interventions: low-protein diet versus control, different low-protein diets versus each other (low-protein diet versus very low-protein diet), low-sodium diet versus control, different low-sodium diets versus each other.

Prescriptions for dietary sodium in patients with chronic kidney disease: how will this shake out?

Patients with chronic kidney disease (CKD) are at risk of exhibiting expanded extracellular volume, and low-sodium diets are often prescribed to limit clinical complications from this condition. Fan et al. performed a post hoc study from the database of the Modification of Diet in Renal Disease Study. Their article, as well as other recent observations, suggests that a low-sodium diet may not be as beneficial as previously thought in all CKD patients.

Vitamin D analogues to target residual proteinuria: potential impact on cardiorenal outcomes

Residual proteinuria, the amount of proteinuria that remains during optimally dosed renin-angiotensin-aldosterone system (RAAS) blockade, is an independent risk factor for progressive renal function loss and cardiovascular complications in chronic kidney disease (CKD) patients. Dual RAAS blockade may reduce residual proteinuria but without translating into improved cardiorenal outcomes at least in diabetic nephropathy; rather, dual RAAS blockade may increase the risk of adverse events. These findings have challenged the concept of residual proteinuria as an absolute treatment target. Therefore, new strategies must be explored to address whether by further reduction of residual proteinuria using interventions not primarily targeting the RAAS benefit in terms of cardiorenal risk reduction would accrue. Both clinical and experimental intervention studies have demonstrated that vitamin D can reduce residual proteinuria through both RAAS-dependent and RAAS-independent pathways. Future research should prospectively explore vitamin D treatment as an adjunct to RAAS blockade in an interventional trial exploring clinically relevant cardiorenal end points.

What determines human sodium intake: policy or physiology?

Past and current U.S. sodium and health policy focused on population-wide reductions in sodium intake. Underlying that policy are a number of assumptions that recent scientific publications challenged. The assumptions include the following: 1) that current intakes are excessive; 2) that the “healthy range” must be below current intakes; 3) that sodium intake can be substantially reduced by public policy; 4) that human intake is dictated by the sodium content of the food supply; and 5) that, unlike all other essential nutrients in which a healthy range is defined by a Gaussian distribution, lower sodium intake is always better. Drawing on the most current published evidence, this review addresses each of these long-standing assumptions. Based on worldwide surveys that assessed sodium intake by 24-h urinary sodium measurements, it is now evident that, across 45 societies and 5 decades, humans consume a reproducible, narrow range of sodium: ∼2600–4800 mg/d. This range is independent of the food supply, verifiable in randomized controlled trials, consistent with the physiologic regulators of sodium intake and is not modifiable by public policy interventions. These findings indicate that human sodium intake is controlled by physiology and cannot be modified by public health policies.