Evidence Summaries

The quality of evidence is downgraded by study limitations (unclear allocation concealment, blinding and incomplete outcome data in half of the trials).

A Cochrane review ¹ included 8 studies with a total of 258 subjects. Duration of the included studies was too short (1 to 26 weeks) to test the effect of salt restriction on endpoints such as mortality, cardiovascular events or chronic kidney disease (CKD) progression. There was a significant reduction in 24 hour sodium excretion associated with low salt interventions (range 52 to 141 mmol) ( MD -105.86 mmol/d, 95% CI -119.20 to -92.51; 8 studies, n=258, I²=51%). Reducing salt intake significantly reduced systolic blood pressure (MD -8.75 mm Hg, 95% CI -11.33 to -6.16; 8 studies, n=258, I²=0%) and diastolic blood pressure (MD -3.70 mm Hg, 95% CI -5.09 to -2.30; 8 studies, n=258,I²=0%). One study reported restricting salt intake reduced the risk of oedema by 56%. Salt restriction increased plasma renin activity and serum aldosterone. Antihypertensive medication dosage was significantly reduced with a low salt diet (RR 5.48, 95% CI 1.27 to 23.66; 2 studies, n=52, I²=0%). There was no significant difference in eGFR, creatinine clearance, serum creatinine, or body weight. Salt restriction significantly reduced urinary protein excretion in all studies that reported proteinuria as an outcome (4 trials, n=149), however data could not be meta-analysed.

A prospective cohort study ² investigated whether an intensive low-salt diet education program effectively attenuated the rate of renal function decline in hypertensive patients with CKD (n=171). During the whole study period, the rate of renal function decline was significantly faster in the conventional group (0.11 ± 4.63 vs. -1.53 ± 3.04 mL/min/1.73 m²/year, p = 0.01). The percent of incremental change in serum creatinine ≥50% was 1.1% in the intensive group and 8.2% in the conventional group (p = 0.025), and the percent of decremental change in eGFR ≥30% was 3.3% in the intensive group and 11.1% in the conventional group (p= 0.048). With logistic regression analysis adjusted for related factors, conventional group showed a higher risk for deterioration in serum creatinine and eGFR.

References

1. McMahon EJ, Campbell KL, Bauer JD et al. Altered dietary salt intake for people with chronic kidney disease. Cochrane Database Syst Rev 2015;(2):CD010070.  [PMID:25691262]

2. Ahn SY, Kim DK, Park JH et al. Long-Term Effects of Intensive Low-Salt Diet Education on Deterioration of Glomerular Filtration Rate among Non-Diabetic Hypertensive Patients with Chronic Kidney Disease. Kidney Blood Press Res 2019;44(5):1101-1114.  [PMID:31533093]