COMMENTARY

Can Drinking More Water Forestall CKD Progression? It's Complicated

Tejas P. Desai, MD

Disclosures

August 30, 2018

I often stress the importance of drinking water for my patients with chronic kidney disease (CKD). Given the choice of beverages available, water seems to be the healthiest option. While I don't "prescribe" water to my patients and I try to avoid the debate of bottled versus tap water, I routinely encourage my patients with early to moderate CKD to drink water plentifully because "it helps the kidneys."

I never considered that my recommendation was not exactly evidence-based. As a result, I was pleasantly surprised by the Chronic Kidney Disease Water Intake Trial (CKD WIT) published in JAMA .[1] The patients enrolled in this randomized controlled trial (RCT) were encouraged to drink water, and authors wanted to determine whether such a simple intervention could stave off the progression of CKD.

The CKD WIT study was a 1-year RCT (not double-blinded) of 631 Canadian patients with stage 3 CKD (data for 590 patients were available for final analysis). The patients who were enrolled in the intervention arm were encouraged by the research staff to increase their water intake by at least 1 L/day. Various measures were taken to ensure that these patients indeed increased their water intake, including plasma copeptin (a surrogate marker for antidiuretic hormone [ADH]), urine outputs, and patient-reported fluid intake.

The primary outcome was the change in the estimated glomerular filtration rate (eGFR; measured by serum creatinine and cystatin-C) after 12 months of randomization. A prespecified secondary outcome included a measurement of creatinine clearance.

Despite having a goal of increasing fluid intake by at least 1 L/day, patients in the intervention group achieved a mean increase of 700 mL/day (95% confidence interval [CI], 600-800 mL/day; P < .001). In association with this increase, the researchers noted both a statistically significant decline in plasma copeptin levels and an increase in 24-hour urine volume.

During the 1-year study period, both patient groups experienced a decline in eGFR, with a greater but nonstatistically significant decline in the intervention group (-2.2 mL/min/1.73 m2 versus -1.9 mL/min/1.73 m2 in the control group). This finding was unchanged regardless of whether the eGFR was measured with creatinine or cystatin-C.

In further subgroup analyses, the presence/absence of macroalbuminuria or diabetes did not alter the differences in eGFR between the groups. Of interest, the creatinine clearance (a secondary outcome) improved in the hydration group (3.6 mL/min/1.73 m2 [95% CI, 0.8-6.4; P = .01]).

The Complicated Part

On its face, CKD WIT does not provide me with the scientific support to recommend increasing water intake. Still, the results don't dissuade me from making this recommendation. For one, the follow-up period of 1 year may be too short to notice a difference. In addition, I am skeptical as to why the creatinine clearance was not a part of the primary outcome. Indeed, noting that Danone Research, the sponsor of the study, suggested that creatinine clearance be included as a secondary outcome raises more questions in my mind as to why the outcome wasn't among the primary outcome measurements.

Nevertheless, I don't see a significant downside to increasing one's water intake. Given the numerous unhealthy beverages one could enjoy, substituting water for caffeinated/carbonated/high-fructose corn syrup-containing drinks seems to be a good idea regardless of the results of CKD WIT.

What do you think? Share your thoughts in the comments section below.

Follow Tejas P. Desai, MD, on Twitter: @nephondemand

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