We’ve all heard the saying, “An apple a day keeps the doctor away.” More recently, patients have been asking about — and nephrologists have been recommending — increased water intake to keep kidney disease away.
For years, a growing number of nephrologists and primary care physicians have been recommending drinking more water to either dilute unrecognized nephrotoxins or just bathe the kidneys in a friendly environment. On the surface, this recommendation seems to make sense, but two studies suggest that our zealous pursuit of imbibing more and more water will not give us the kidney protection we’re hoping for.
About 4 years ago, researchers from Canada performed the decently sized but underpowered CKD WIT randomized clinical trial to determine whether increased water intake would slow the rate of kidney decline. Over a 1-year follow-up period, well-matched patients with chronic kidney disease stage 3 or worse were told to increase their daily water intake by 1.0-1.5 L/d vs making no change at all. Using the estimated glomerular filtration rate (eGFR) equation (creatinine-based or cystatin C–based), the extra water consumed in the intervention group did not protect kidney function.
Although a major limitation was a possible lack of adherence to increased water intake (most patients had an increased urine output by only 600 mL/d), CKD WIT was my first scientific exposure to the notion that water wasn’t as kidney-protective as once thought.
Nonetheless, organizations remain focused on the renal benefits of increasing water intake. Short clinical studies show that water intake can lower fasting glucose levels or sufficiently restore hemodynamic stability. These are small studies with short follow-up periods, so the true benefits of water intake can’t be accurately assessed.
To help resolve this issue, investigators of the CKD-REIN study undertook a 3-year prospective trial of 1265 patients with stage 3 or worse chronic kidney disease to determine which, if any, amount of water intake would reduce decline in kidney function.
Their investigation showed that participants who lowered their urine osmolarity from a baseline of 374 mOsm/L to < 326 mOsm/L had the greatest drop in eGFR (creatinine-based). Individuals who drank the least or most amount of water daily (< 0.5 or > 2.0 L/d, respectively) had the greatest likelihood of experiencing kidney decline (hazard ratio, 1.92 and 2.43, respectively) compared with those who had moderate water intake (1.0-1.5 L/d).
What Should We Tell Patients?
All of this means that we should no longer be focused on the amount of water one drinks. It’s still safe to recommend some water intake over none, but drinking excessive amounts of water will not confer any protection.
CKD WIT and CKD-REIN have called into question the belief that we can simply bathe the kidneys with water and all will be well. Just as an apple a day won’t actually keep the doctor away, guzzling water won’t prevent kidney disease. Moderate water consumption is all we can recommend on the basis of the available science.
Reference:
https://www.medscape.com/viewarticle/956731
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