Low-Osmolar Diet and Adjusted Water Intake for Vasopressin Reduction in Autosomal Dominant Polycystic Kidney Disease: A Pilot Randomized Controlled Trial

Background:Autosomal dominant polycystic kidney disease (ADPKD) affects millions of people worldwide. Vasopressin promotes disease progression. Study Design:A randomized controlled trial with equal (1:1) allocation. Setting & Participants:This trial examined the effect of combining a low-osmolar (low-sodium [1,500 mg/d], low-protein [0.8 g per kilogram of body weight]) diet and adjusted water intake on vasopressin secretion in 34 patients with ADPKD. Intervention:Participants were randomly assigned to receive a low-osmolar diet followed by adjusted water intake to achieve urine osmolality <= 280 mOsm/kg water versus no intervention for 2 weeks. Outcome:The primary outcome of the study was change (delta) in copeptin levels and urine osmolality between the intervention and control groups from baseline to 2 weeks. Measurements:Fasting plasma copeptin level, 24-hour urine osmolality, and total solute intake. Results:Baseline characteristics of the 2 groups were similar. Mean plasma copeptin levels and urine osmolality declined from 6.2 +/- 3.05 (SD) to 5.3 +/- 2.5 pmol/L (P=0.02) and from 426 +/- 193 to 258 +/- 117 mOsm/kg water (P=0.01), respectively, in the intervention group compared to a nonsignificant change in the control group (from 4.7 +/- 3.6 to 5.07 +/- 4 pmol/L [P=0.2] and 329 +/- 159 to 349 +/- 139 mOsm/kg water [P=0.3], respectively). The change in copeptin levels (primary outcome) and urine osmolality was statistically significant between the intervention and control groups (delta copeptin, 20.86 +/- 1.3 vs 10.39 +/- 1.2 pmol/L [P = 0.009]; delta urine osmolality, 2167 +/- 264 vs 120 +/- 80 mOsm/kg water [P=0.007], respectively). Total urinary solute decreased in only the intervention group and significantly differed between groups at week 1 (P=0.03), reducing mean water prescription from 3.2 to 2.6 L/d. Limitations:Small sample size and short follow-up. Conclusions:We developed a stepwise dietary intervention that led to a significant reduction in vasopressin secretion in patients with ADPKD. Furthermore, this intervention led to a reduction in water required for vasopressin reduction. (C) 2016 by the National Kidney Foundation, Inc.