Salt intake correlates with night systolic blood pressure in non-dialytic chronic kidney disease

Lowering salt intake is a cornerstone strategy to optimize blood pressure (BP) control in chronic kidney disease (CKD) [1–3], although recent studies have raised some concerns about the real benefit of a low salt diet on the renal prognosis in hypertensive and CKD patients [4–6]. Increased salt intake induces abnormalities in circadian BP rhythm likely due to incapacity to excrete sodium or enhanced sodium tubular reabsorption [7–9]. Indeed, nocturnal hypertension is a common condition in CKD patients and is more predictive than office BP of poor cardio-renal outcomes [10]. Nonetheless, the relationship between salt intake and nocturnal BP has been poorly investigated in these patients [11]. To gain more insights on this issue, we used data from a recent 6-month multicentre randomized trial that evaluated the effect of self-measurement of urinary chloride on adherence to a low sodium diet [24 h urinary sodium excretion (24hUNa) <100 mmol/day] and BP control in 138 CKD patients [12]. During this trial, 24-h ambulatory BP (ABP), estimated glomerular filtration rate (eGFR) and 24hUNa were measured at baseline and months 3 and 6 in each patient. As the trial did not show a substantial difference in 24hUNa and ABP over time, we pooled the data of the two groups and averaged the three measurements to reduce the intrinsic variability of these parameters. A single measurement of 24hUNa is traditionally used to assess dietary salt intake. However, recent studies have highlighted the relevance of multiple urinary measurements to assess salt intake properly when testing associations between this variable and clinical outcomes [1, 2, 13].