Effect of dietary salt reduction on blood pressure in kidney transplant patients: a randomised controlled trial

Abstract Background and Aims Cardiovascular morbidity and mortality are increased in kidney transplant patients. High blood pressure (BP) contributes significantly to this risk and is associated with shortened allograft survival. Dietary salt reduction is widely recommended as a strategy to lower BP in the general population and in chronic kidney disease. Due to a lack of evidence there is currently no consensus on dietary salt restriction in kidney transplant patients. The primary aim of the study was to examine the impact of reduced dietary salt intake on BP in kidney transplant patients. Method Sixty stable kidney transplant patients, ≥ 6-months post-transplantation, with BP ≥120/80 mmHg, and sodium intake ≥80 mmol/24hrs, were randomised in this parallel-designed study to receive either a regular-salt diet (target 150 mmol/24hr) or a low-salt diet (target 80 mmol/24hr) for 8-weeks. The primary outcome measure was systolic and diastolic BP. Secondary outcome measures included 24-hour ambulatory BP (ABP) and proteinuria. Dietary salt intake was assessed by 48-hour urinary sodium excretion. Results At baseline, patients (72% men) were 56±11 years with estimated glomerular filtration rate (eGFR) 53±18 mL/min/1.73m2. Mean urinary sodium was 128±42 mmol/24hr, mean systolic BP was 132±12 mmHg, and mean diastolic BP was 77±10 mmHg. At the end of the intervention period sodium excretion was significantly lower in the low-salt group compared with the regular-salt group (90±37 vs. 132±51 mmol/24hr; adjusted mean difference, -36 [95% CI, -59 to -14] mmol/24hr; P=0.002). We found no difference in systolic BP (adjusted mean difference, -2 [95% CI, -12 to 9] mmHg; P=0.750), diastolic BP (adjusted mean difference, 0 [95% CI, -4 to 4] mmHg; P=0.887), 24-hour systolic ABP (adjusted mean difference, -3 [95% CI, -9 to 2] mmHg; P=0.213) or 24-hour diastolic ABP (adjusted mean difference, -2 [95% CI, -5 to 1] mmHg; P=0.267). There was no significant effect on proteinuria or eGFR. Conclusion In this study baseline urinary sodium was lower than expected and baseline BP was well controlled. Reducing dietary salt by 2g/day did not have a significant effect on office blood pressure readings.