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Table 1 Studies reporting a relationship between fluid intake and/or urinary hydration biomarkers and health outcomes related to urine dilution: kidney stones and urinary tract infection

From: Hydration for health hypothesis: a narrative review of supporting evidence

Author (year)
Study type, cohort name, follow-up period
Fluid intake or urinary hydration marker associated with health outcome Health Outcome (Risk or Benefit)
Total fluid intake volume (TFI, L·day−1) 24-h urine volume (UVol, L·day−1) or Urine osmolality (UOsm, mOsm·kg−1)
Borghi et al. (1996) [23]
Recurrent stone formers
vs. healthy controls
  UVol, Mean [sd]
Stone formers: 1.04 [0.24]
Controls: 1.35 [0.53]
Risk: Stone formers had lower spontaneous 24 h urine volume than age, sex, body weight, and socioeconomic-matched controls
Borghi et al. (1996) [23]
RCT, 5-year follow-up
Recurrent stone formers
  UVol, Mean [sd]
Pre: 1.1 [0.2]
Post: 2.6 [0.4]
Pre: 1.0 [0.2]
Post: 1.0 [0.2]
Benefit: Increasing urine volume reduced kidney stone recurrence (12% vs. 27% in control group), time between episodes, and urine supersaturation in stone formers
Curhan et al. (2004) [117]
Prospective, NHS II cohort, 8-year follow-up
General population (women)
TFI, quintiles
Q1: ≤ 1.43
Q2: 1.43–1.85
Q3: 1.85–2.25
Q4: 2.25–2.77
Q5: ≥ 2.77
  Benefit: Reduction in multivariate-adjusted RR for incident kidney stones in women in Q3, Q4, and Q5 (RR 0.79, 0.72, and 0.68, respectively), compared to reference (women with FI ≤ 1.43 L·day−1)
Curhan & Taylor (2008) [24]
Pooled retrospective study of 3 cohorts (NHS I, NHS II, HPFS)
General population
  UVol, Cutoff value
From 1.5 to ≥ 2.5
Benefit: Across three cohorts including 2,237 stone formers, individuals with a urine volume ranging from 1.5L to more than 2.5L·day−1 were shown to be at lower risk of developing kidney stones with corresponding RR ranging from 0.46 (urine volume 1.5 to 1.74L·day−1) to 0.22 (urine volume ≥ 2,5 L·day−1), compared to reference (urine volume ≤ 1.0L·day−1)
Curhan et al. (1993) [22]
Prospective cohort (HPFS), 4-year follow up
General population (men)
TFI, quintiles
Q1: < 1.28
Q2: 1.28–1.67
Q3: 1.67–2.05
Q4: 2.05–2.54
Q5: ≥ 2.54
  Benefit: Reduction in multivariate-adjusted RR for incident kidney stones in men in Q5 (RR = 0.71), compared to reference (men with FI < 1.28 L·day−1)
Hooton et al. (2018) [42]
RCT, 12-month follow-up
Recurrent UTI (women)
TFI (intervention group), Mean [sd]
Pre: 1.1 [0.1]
Post: 2.8 [0.2]
UVol (intervention group), Mean [sd]
Pre: 0.9 [0.2]
Post: 2.2 [0.3]
UOsm (intervention group), Mean [sd]
Pre: 721 [169]
Post: 329 [117]
Benefit: 48% reduction in UTI recurrence in intervention group vs. control; increased time between episodes; reduction in antibiotic use
  1. Empty cells denote that this variable was not reported
  2. HPFS Health Professionals Follow-Up Study; NHS I Nurses’ Health Study; NHS II Nurses’ Health Study II; RCT Randomized Controlled Trial; RR Relative risk; sd Standard Deviation; TFI Total Fluid Intake, volume of drinking water plus other beverages; UTI Urinary Tract Infection