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 [1,500mg/d], low-protein [0.8g 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 ≤ 280mOsm/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±2.5pmol/L (P=0.02) and from 426±193 to 258±117mOsm/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±4pmol/L [P=0.2] and 329±159 to 349±139mOsm/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, -0.86±1.3 vs +0.39±1.2pmol/L [P=0.009]; delta urine osmolality, -167±264 vs +20±80mOsm/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 2.6L/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.