Coaching to improve water intake does not improve kidney function in adults with chronic kidney disease

1. In this randomized controlled trial, coaching to improve daily fluid intake did not improve kidney function in patients with Chronic Kidney Disease.

2. Increasing fluid intake via coaching was adequate to lower vasopressin secretion in patients.

Evidence Rating Level: 1 (Excellent)

Study Rundown: In both preclinical animal models and clinical human studies, increased water intake has improved kidney function. However, these findings have often been in adults with normal kidney function, and there is a lack of scientific evidence on the benefits of water intake in patients with chronic kidney disease (CKD). In this randomized control trial, the effect of coaching to improve kidney function in patients with CKD was compared to a control group that maintained usual fluid intake. After one year, the coaching group drank on average about a half liter more per day than the control group, but the mean change in GFR between the coaching and control groups were similar. The hydration group did have reduced plasma vasopressin concentration, however.

While this study suggests that coaching to increase water intake does not slow decline in kidney function in patients with CKD, a few limitations should preclude this conclusion. First, while the patient were able to increase their fluid consumption with coaching, the study targeted a 1.0 to 1.5L increase in water intake per day, and this goal was not met, underscoring the difficulty in obtaining a large, sustained increase in routine practice. In addition, the study was underpowered to detect clinically important differences. Therefore, further research is required to understand the benefits of increased water intake in this patient population.

Click to read the study, published in JAMA

Relevant Reading: “Drink at least eight glasses of water a day.” Really? Is there scientific evidence for “8 × 8”?

In-Depth [randomized control trial]: The current study is a parallel-study randomized control trial that included adults with stage 3 CKD from 9 different Canadian clinics in Ontario. Patients in the coaching group were coached to increased their fluid intake by 1.0 to 1.5L per day depending on their sex and weight for the duration of the 1-year trial. Patients in control group maintained their fluid intake or reduced it by 0.25 to 0.5L per day based on pre-randomization urine output and 24-hour urine osmolality. Patients were individually coached at monthly intervals over 12 months. The primary outcome was 1-year change in eGFR from enrollment to 12 months after randomization. Secondary outcomes included 1-year change in plasma copeptin concentration (proxy for vasopressin secretion), creatinine clearance, 24-hour urine albumin, and patient reported quality of life.

The study originally intended to recruit 700 patients but only 631 could be randomized due to reasons including budget and trial length. Overall, of the 631 randomized participants, mean age was 65.0, males 63.4%, and median urine albumin 123 mg/dL. At 1-year follow-up, the coaching group had increased water intake by 0.6L (CI95 0.5 to 0.7) per day on average. Mean change in eGFR was similar between groups (adjusted between-group difference -0.3 mL/min/1.73 m2; CI95 -1.8 to 1.2). For secondary outcomes, mean between-group differences favoring the coaching group were detected for plasma copeptin (-2.2pmol/L; CI95 -3.9 to -0.5) and creatinine clearance (3.6 mL/min/1.73m2; CI95 0.8 to 6.4) but not for urine albumin (7 mg/d; CI95 -4 to 51) and quality of life (0.2 points; CI95 -0.3 to 0.3).

Image: PD

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