Jury still out on whether drinking more water protects against CKD progression
Drinking more water did not significantly slow down the decline in kidney function of patients with stage 3 chronic kidney disease (CKD) at 1 year compared with patients who maintained their daily water intake, the CKD WIT* randomized study suggests.
The age-old advice of “drink at least eight glasses of water a day” comes not from primary research, as the researchers noted, but from the US food and Nutrition Board in 1945. [Natl Res Counc 1945;No. 122:3-18; Am J Physiol Regul Integr Comp Physiol 2002;283:R993-R1004]
“Despite widespread beliefs, little scientific data exists on the optimal amount of water to drink,” said lead author Dr William Clark of Schulich School of Medicine & Dentistry at Western University in Ontario, Canada.
In the multicentre parallel-group study, 631 patients (mean age 65 years, 63.4 percent men) with stage 3 CKD (eGFR of 30–60 mL/min/1.73 m2 and micro-/macroalbuminuria) were randomized to coaching to increase (by 1.0–1.5 L) or maintain their daily water intake. Out of the total population, 590 patients survived and had data available at 1-year follow-up. The hydration group had 0.6 L more urine volume per 24 hours than the control group (p<0.001), indicating adherence to increase fluid intake. [JAMA 2018;319:1870-1879]
After 1 year, increased water intake did not delay the loss of kidney function, as indicated by similar changes in eGFR in the hydration and control groups (-2.2 vs -1.9 mL/min/1.73 m2; p=0.74). The finding remained in per-protocol analysis, as well as subgroup analyses prespecified by presence of macroalbuminuria, diabetes, and eGFR <45 mL/min/1.73 m2.
Nonetheless, increased water intake did lead to significantly reduced release of the antidiuretic hormone vasopressin, as reflected in the 2.2 pmol/L lower plasma copeptin level in the hydration group compared with the control group (-1.4 vs 0.8 pmol/L; p=0.01).
Creatinine clearance was also significantly higher by 3.6 mL/min/1.73 m2 with greater water intake vs control (p=0.01).
Other secondary measures such as urine albumin and quality of health did not differ significantly between the two groups.
“This research indicates that for most patients with CKD, increasing fluid intake will not stop further loss of kidney function. It does allow us then to focus our efforts on other potential therapeutic options,” said Clark.
According to the researchers, current treatment guidelines for managing CKD are limited. Management strategies include medication and controlling blood pressure through restriction of salt consumption and increased water intake.
“We do know that many patients are drinking well below the recommended amounts. More research is needed, but the goal would be to tailor increased water intake as a treatment to those patients [drinking below the recommended amount],” suggested Clark.
“The absence of an effect of drinking more water on eGFR may be interpreted in several ways,” wrote Clark and co-authors. A greater increase in water intake or follow-up longer than a year may be required to detect a significant effect on eGFR.
Furthermore, as the study was powered (up to 80 percent) to detect 2 mL/min/1.73 m2 difference in eGFR change between groups, “the study may have been underpowered to detect … the prespecified minimal clinically important difference of 1 mL/min/1.73 m2,” according to the researchers.
Although drinking more water did not appear to protect against declining kidney function in the current study, drinking large amount of water is still important as it has been associated with a lower risk of kidney stones. [Ann Intern Med 2014;161:659-667; J Urol 1996;155:839-843]