Low Salt Diet Improves Blood Pressure in CKD

Packaged foods tend to contain excess sodium.
Packaged foods tend to contain excess sodium.

Nephrologists may improve the health and quality of life of non-dialysis chronic kidney disease (CKD) patients by encouraging dietary sodium restriction and counseling from a registered dietitian.

Limiting dietary sodium to 2000 mg a day clinically and significantly reduced 24-hour ambulatory systolic blood pressure by 10.8 mmHg and excess fluid retention over 4 weeks, compared with usual diet. Whole-body extracellular volume and calf-intracellular volume decreased by 1.02 L and 0.06 L, respectively. Urinary sodium excretion decreased by 57.3 mEq/24 hours and weight decreased by 2.3 kg. The results of the blinded, randomized, crossover trial of 58 stage 3 to 4 CKD patients were published online ahead of print in the Clinical Journal of the American Society of Nephrology.

“Optimal BP control remains a cornerstone of CKD management,” Rajiv Saran, MD, of the University of Michigan, Ann Arbor, and colleagues wrote. “In this randomized crossover trial, we have demonstrated the feasibility and efficacy of dietary sodium restriction using motivational interviewing without invoking preprepared meals in effecting meaningful improvements in both hydration status and BP among patients with CKD.”

CKD patients are purported to have “salt-sensitive” blood pressure. Reducing fluid retention and blood pressure by lowering dietary sodium intake may help slow CKD progression, along with other strategies. The 2012 Kidney Disease: Improving Global Outcomes (KDIGO) blood pressure guidelines recommend limiting dietary sodium to 2000 mg daily.

With regard to the intervention, patients did not receive food provisions, but implemented advice given by registered dietitians. Each week, a dietitian provided individualized counseling, either in person or by phone, using the patient's 3-day food diary for reference. The dietitian employed motivational interviewing techniques to overcome resistance to change and empower lower sodium choices.

A majority of patients (79%) reduced their dietary sodium intake, including 65% who reduced their intake by more than 20%. However, a dietitian's ongoing support may be necessary to maintain adherence to a low sodium diet because patients' urinary sodium excretion returned to usual levels after the sodium-restricted phase of the study.

Notably, albuminuria did not decline as expected, warranting further research. Patients' baseline proteinuria was modest, however. Mean serum creatinine rose slightly by 0.1 mg/dL, which might reflect dips in intraglomerular pressure, according to the investigators. Albumin-to-creatinine ratio did not change significantly.

Limiting dietary sodium may reduce the number of antihypertensive medications patients need to take. At enrollment, most patients were taking at least one blood pressure medication and half were taking 3 or more. More patients discontinued a medication during the sodium restricted diet phase of the study than the usual diet phase.

Participants were advised to keep their daily calories and fat intake the same (while restricting potassium and phosphorus) throughout the study. They were also asked to maintain usual habits with regard to alcohol, caffeine, nicotine, and physical activity. Given the incremental weight loss experienced by participants, however, the investigators speculated that regular contact with the dietitian may have fostered healthier eating and exercise.

A low sodium diet may also reduce renal and cardiovascular risks in other ways, such as preventing left ventricular diastolic dysfunction.

The study was conducted at 2 centers: the University of Michigan and the University of North Carolina at Chapel Hill. Patients with salt wasting disease were excluded. During the study, 2 participants experienced hypotension, but it did not require medical treatment.

 

Reference

1.Saran R, Padilla RL, Gillespie BW, et al. A Randomized Crossover Trial of Dietary Sodium Restriction in Stage 3-4 Chronic Kidney Disease. CJASN February 16, 2017. doi: 10.2215/CJN.01120216 [Epub before print]

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