Reviews/Electrolytes and Hydration/Water intake prevents kidney stones
Health · EHYD-HEA-01 · v2
Borderline: within 4 points of the Uncertain/Doubtful boundary, so a re-grade could land either side.
Drinking more water is widely advised to stop kidney stones coming back, and the biology behind it is reasonable: more fluid makes more dilute urine. But when a large trial actually tracked whether stone formers had fewer stone events over two years, a programme designed to push up fluid intake did not produce significantly fewer recurrences than ordinary care [1]. The other included trials only measured how much urine people produced, not whether they got fewer stones [2][4]. So the corpus shows the approach can nudge urine volume up a little, yet the one study that measured real stone recurrence did not find a benefit. Because that single trial's result leaves room for either a small real effect or none, the panel treated the clinical claim as genuinely unsettled rather than proven.
The corpus contains one large randomised trial measuring the claim's actual clinical endpoint — symptomatic stone recurrence in stone formers — and it was null: 154 (19%) events in the intervention group versus 165 (20%) in control, hazard ratio 0.96 (95% CI 0.77-1.20) [1]. That same trial found 24h urine volume rose modestly in both arms and was higher in the intervention group, and no difference in stone growth or new stones [1]. The two supporting trials measured only the surrogate of urine volume: a smart bottle raised mean volume more than dietary advice alone [2], and urine output rose 0.4 L across all arms with smart technology adding nothing beyond counselling [4]. The corpus therefore demonstrates that interventions can slightly raise urine volume but does not demonstrate fewer stone events. The contested point: The division is whether a modest, achievable increase in urine volume translates into fewer actual stones. The surrogate trials [2][4] show volume can be raised, but [1] shows that in practice a raised-volume intervention did not cut recurrence, while its confidence interval (0.77-1.20) neither confirms nor rules out a real benefit.
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One reviewer's only job is to attack the finding. The challenges below were weighed before the grade was set.
The single hard-outcome trial [1] is null (HR 0.96, 95% CI 0.77-1.20): the most directly relevant evidence in the corpus fails to show the claimed reduction in recurrent stones.
All supporting included evidence ([2],[4]) reaches only the surrogate of 24h urine volume; [1] shows that a modest volume increase did not translate into fewer stones, so surrogate gains cannot substantiate the clinical claim.
Where it remains uncertain. Supporting trials show urine volume can be modestly raised [2][4], but [1] shows that increase did not translate into fewer stones, and its CI leaves a real benefit neither confirmed nor excluded.
Aleatory
Recurrence was counted from 154 vs 165 events over two years [1]; random variation in a finite number of events leaves genuine imprecision around the hazard ratio.
The load-bearing papers from a corpus of 12, each classified by what it does to the claim. Every DOI is taken from the corpus the claim was graded on.
Direct, large-N clinical endpoint: higher-fluid intervention did not significantly reduce recurrent symptomatic stones.
“A behavioural intervention programme to promote fluid intake for secondary stone prevention did not reduce recurrent stone events but modestly increased urine volume compared with guideline-based care during a 2-year follow-up period.”
Panel auditInternal validity: high · scope of inference: Adults and adolescents 12+ with a history of urinary stones and low 24h urine volume; 66.6% were recurrent stone formers; 2-year follow-up.Key limitations: intervention only modestly raised urine volume · tests an adherence intervention, not a clean high-vs-low intake contrast · 2-year follow-up may be short for recurrence
Surrogate support: an intervention can raise 24h urine volume in stone formers, but recurrence is not measured.
“The mean increase in volume was greater in the SB arm (1.37 L, 95% confidence interval -0.51 to 3.25) than the DR arm (0.79 L, 95% confidence interval -1.15 to 2.73) (P = .04).”
Panel auditInternal validity: medium · scope of inference: Adults with nephrolithiasis and low urine volume (<1.5 L), over 6-12 weeks; speaks to urine volume, not stone events.Key limitations: no stone outcome · high dropout · short duration · manufacturer-related device
Surrogate support: counselling raised urine output across arms; again no stone-recurrence endpoint.
“Overall mean UOP increased by 0.4 L in each group (p < 0.05), with no difference in mean baseline 24 h UOP (1.6 L) and 12 month 24 h UOP (2.0 L) between groups (p > 0.05).”
Panel auditInternal validity: low · scope of inference: Nephrolithiasis patients with low urine output over 12 months; speaks to urine output and adherence, not stone events.Key limitations: no stone outcome · severe attrition · surrogate endpoint
3 of 12 papers shown. The full review lists all of them, with the panel’s arbitration →
Claims are graded at each quarterly release, and re-graded between releases only when a pivotal trial lands. Every change is a new version of the claim.
A large direct RCT null on the clinical endpoint, with only surrogate support otherwise and a confidence interval that neither confirms nor excludes benefit, places the claim at genuine equipoise rather than supported.
Release 2026-q4 re-graded every claim from its corpus under protocol v0.19. An earlier release's grade is shown for the record; it came from an earlier protocol and is not a movement.
Assumptions that carry weight but are not themselves established.
The panel records the gap that would most move the claim, and the study that would close it.
Recurrence at an achieved urine-volume target. The claim turns on whether reaching high urine volume cuts stones, but [1] only modestly raised volume and was null, while [2][4] never measured recurrence. The panel rates this the highest-importance open gap for the claim, and names the study design that would close it: A trial powered on symptomatic recurrence that enrols or analyses participants who demonstrably sustain a high urine-output target, rather than assignment to an intervention programme.
Open question: Does achieving and sustaining a high urine volume, rather than being assigned to a fluid-intake programme, reduce symptomatic stone recurrence? Why it is still open: [1] was null but only modestly raised volume with challenging adherence, and its CI (0.77-1.20) does not exclude a benefit; [2][4] measured only volume.
Priors is a sceptical first reader, not peer review, and not medical advice.
Release 2026-q4 · graded 21 Oct 2026 · protocol v0.19