Internal medicine

Osmole

Hazard ratio

Interquartile range

Urology

Renal function

Urine osmolality

Urine

Kidney

Kidney disease

Cohort

Confidence interval

Medicine

Nephrology Dialysis Transplantation

Optimal daily water intake to prevent chronic kidney disease (CKD) progression is unknown. Taking the kidney's urine-concentrating ability into account, we studied the relation of kidney outcomes in patients with CKD to total and plain water intake and urine volume.Including 1265 CKD patients [median age 69 years; mean estimated glomerular filtration rate (eGFR) 32 mL/min/1.73 m2] from the Chronic Kidney Disease-Renal Epidemiology and Information Network cohort (2013-19), we assessed fluid intake at baseline interviews, collected 24-h urine volumes and estimated urine osmolarity (eUosm). Using Cox and then linear mixed models, we estimated hazard ratios (HRs) and 95% confidence intervals (CIs) for kidney failure and eGFR decline associated with hydration markers, adjusting for CKD progression risk factors and eUosm.Patients' median daily intake was 2.0 L [interquartile range (IQR) 1.6-2.6] for total water and 1.5 L (1-1.7) for plain water, median urine volume was 1.9 L/24 h (IQR 1.6-2.4) and mean eUosm was 374 ± 104 mosm/L. Neither total water intake nor urine volume was associated with either kidney outcome. Kidney failure risk increased significantly with decreasing eUosm ˂292 mosm/L. Adjusted HRs (95% CIs) for kidney failure associated with plain water intake were 1.88 (1.02-3.47), 1.59 (1.06-2.38), 1.76 (0.95-3.24) and 1.55 (1.03-2.32) in patients drinking <0.5, 0.5-1.0, 1.5-2.0 and >2.0 L/day compared with those drinking 1.0-1.5 L/day. High plain water intake was also significantly associated with faster eGFR decline.In patients with CKD, the relation between plain water intake and progression to kidney failure appears to be U-shaped. Both low and high intake may not be beneficial in CKD.

Water intake and progression of chronic kidney disease: the CKD-REIN cohort study