We performed this review to find out whether drinking more water prevents people from getting kidney stones.
Kidney stones are common in people. Drinking more water may prevent people who have never had stones to get stones and/or help people who have had stones in the past to get them again. We are uncertain how well this works and whether drinking more water has unwanted effects.
We examined research published up to October 2019. We included studies which by chance decided whether people were asked to drink more water (to produce at least 2 litres of urine) or were given no special instructions. We found no studies of people who had never had kidney stones. We found one study, performed in 220 people who had calcium-containing stones in the past, but were stone-free when they started the study. The average age was approximately 41 years, and two-thirds of participants were men.
We found that drinking more water may reduce the risk of stones coming back. It may also prolong the time it takes for stones to come back. We found no evidence of unwanted effects.
Certainty of evidence
The certainty of evidence for both outcomes for which we found evidence was low. This means that the true results may be quite different.
We found no RCT evidence on the role of increased water intake for primary prevention of urinary stones. For secondary prevention, increased water intake achieving a urine volume of at least 2.0 L/day may reduce urinary stone recurrence and prolong time to recurrence for people with a history of urinary stone disease. However, our confidence in these findings is limited. We did not find evidence for adverse events.
Urinary stone disease is a common condition characterised by increasing prevalence and high rates of recurrence. Observational studies have reported that increased water intake played a role in the prevention of urinary stone formation but with limited strength of evidence.
To compare the effects of increased water intake with standard water intake for the prevention of urinary stone formation in participants with or without a history of urinary stones.
We performed a systematic search of PubMed (MEDLINE), EMBASE (Ovid) and the Cochrane Library to 15 October 2019. We handsearched review articles, clinical trial registries, and reference lists of retrieved articles. We did not apply any restrictions to publication language or publication status.
We included randomised controlled trials (RCTs) and quasi-RCTs looking at the benefits and harms of increased water intake versus standard water intake for the prevention of urinary stone formation in participants with or without a history of urinary stones.
We used standard methodological procedures expected by Cochrane. Two review authors independently extracted data and assessed the risk of bias of included studies. We pooled dichotomous outcomes (e.g. incidence/recurrence rate of urinary stones; adverse events) using risk ratios (RRs) with 95% confidence intervals (CIs). We calculated hazard ratio (HRs) and corresponding 95% CIs to assess the intervention effect for time-to-event outcomes. We assessed the certainty of the evidence by using the GRADE criteria.
Our search identified no RCTs investigating the role of increased water intake for the prevention of urinary stone formation in participants with no history of urinary stones (primary prevention). We found one RCT assessing the effects of increased water intake versus standard water intake for the prevention of urinary stone formation in people with a history of urinary stones (secondary prevention). This trial randomised 220 participants (110 participants in the intervention group with increased water intake and 110 in the control group with standard water intake). Increased water intake was defined as achieving a urine volume of at least 2.0 L per day by drinking water.
Based on this study, increased water intake may decrease stone recurrences (RR 0.45, 95% CI 0.24 to 0.84; 199 participants; low-certainty evidence); this corresponds to 149 fewer (43 fewer to 205 fewer) stone recurrences per 1000 participants with 270 stone recurrence per 1000 participants over five years in the control group.
Increased water intake may also prolong the time to urinary stone recurrence compared to standard water intake (HR 0.40, 95% CI 0.20 to 0.79; 199 participants; low-certainty evidence); based on a stone recurrence rate of 270 per 1000 participants over five years, this corresponds to 152 fewer (209 fewer to 50 fewer) recurrences per 1000 participants.
For both outcomes we downgraded the certainty of evidence for study limitations and imprecision. We found no evidence for the outcome of adverse events