Coaching chronic kidney disease (CKD) patients to increase their usual water intake does not slow kidney function decline over 1 year, according to new study findings published in the Journal of the American Medical Association.

For the CKD WIT (Chronic Kidney Disease Water Intake Trial) trial, William F. Clark, MD, of Victoria Hospital in London, Ontario, and colleagues randomly assigned 590 stage 3 CKD patients (mean age 65 years; 63.4% men) with 24-hour urine volume of less than 3.0 L to increase or maintain their usual water intake. Patients in the hydration group were coached by phone to drink an additional 1.0 to 1.5 L of water daily, depending on their sex and weight. Patients in the control group maintained their usual fluid intake or decreased it by 0.25 to 0.5 L per day if baseline 24-hour urine volume was greater than 1.5 L per day and 24-hour urine osmolality less than 500 mOsm/kg. At baseline, mean estimated glomerular filtration (eGFR) rate was 43 mL/min/1.73 m2 and median urine albumin 123 mg/day.

After 1 year, 24-hour urine volume was a significant 0.6 L per day higher in the hydration group. Yet both groups experienced similar eGFR decline: −2.2 vs -1.9 mL/min/1.73m2 in the hydration and control groups, respectively. The hydration group also had lower plasma copeptin (-2.2 pmol/L), and higher creatinine clearance (3.6 mL/min/1.73m2), urine albumin (7mg/d), and quality of health (0.2 points).

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According to investigators, increased water intake may not slow kidney function decline, or even higher amounts of water or longer follow up may be needed. It also is possible that the study is underpowered to detect a small clinical difference.

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Clark WF, Sontrop JM, Huang SH, et al. Effect of coaching to increase water intake on kidney function decline in adults with chronic kidney disease: The CKD WIT randomized clinical trial.  JAMA. 2018;319(18):1870-1879. doi:10.1001/jama.2018.4930