A KANG1, F NERBASS2,3, R PECOITS-FILHO1,2,3, B NEAL1, M JARDINE1
1The George Institute for Global Health, University Of New South Wales, Sydney, Newtown, Australia, 2Pro-Rim Foundation, Joinville, Brazil, 3Pontificia Universidade Catolica do Parana, , Curitiba, Brazil
Aim: Determine the short and long-term impact of dietary sodium reduction on estimated glomerular filtration rate (eGFR) in chronic kidney disease (CKD).
Background: Dietary sodium reduction improves blood pressure (BP), an important predictor of CKD progression. In healthy subjects, sodium restriction leads to a short-term reduction in eGFR. The long-term effects of dietary sodium reduction have greater clinical importance.
Methods: We performed a systematic review of randomised controlled trials of higher versus lower sodium consumption in people with CKD (eGFR<60ml/min or as defined by study authors). We searched the Cochrane central register of controlled trials, MEDLINE, EMBASE, and clinicaltrials.gov with a pre-specified strategy. Two reviewers independently assessed studies and extracted data. Outcomes included eGFR, albuminuria and BP. Prespecified subgroups were short- and long-term (<3 months, ≥3 months) study duration. The effect on outcomes was meta-analysed using random effects models.
Results: From 2245 references, 20 trials were identified reporting outcomes of interest representing 1038 people with CKD. Mean follow-up was 8.1[range:1-24] weeks with only 3 trials ≥3 months. Separation in dietary sodium was achieved through either dietary (15) or combined sodium supplementation +/- dietary-based (5) interventions. Lower dietary sodium improved BP (SBP-5.83[-7.78 to -3.88]/ DBP-2.92[-3.88 to -1.95]mmHg). There was no overall difference in eGFR (-0.39[-3.13 to 2.35]ml/min/1.73m2, heterogeneity I² 55%) or albuminuria (1.13[-1.42 to 1.12] mg/day I² 0%). Trial duration made no difference to the impact of lower dietary sodium on eGFR (short-term -3.40[-8.12 to 1.31]; long-term 1.69[-0.58 to 3.96]ml/min/1.73m2, p 0.06.
Conclusion: In CKD, dietary sodium reduction improves BP but not albuminuria. With few longer term studies, there is currently insufficient evidence to determine the long-term effect of sodium reduction on renal function.
Amy Kang is nephrologist and PhD student at the George Institute for Global Health, UNSW, Sydney.