IntroductionEpidemiologyI. Epidemiology of kidney stonesI.1. Prevalence of kidney stonesI.2. An increasing trend in childrenPathophysiology II. Pathophysiology of kidney stonesII.1. LithogenesisII.1.1. Urine supersaturation : the driving force of crystallogenesisII.1.2. Promoters and inhibitors of stone formationII.2. Urine volume and composition: a necessary balanceRisk factorsIII. Risk factors for kidney stonesIII.1. Individual, non-modifiable risk factorsIII.1.1 Family historyIII.1.2. Race and ethnicityIII.1.3. Age and genderIII.1.4. Current change in gender prevalenceIII.2. Lifestyle related factorsIII.2.1. Calcium intakeIII.2.2. Emerging dietary risk factorsIII.2.3. Association with other chronic diseasesDehydrationIV. Dehydration: a risk factor for kidney stonesIV.1. Low urine volume: a key risk factor for kidney stonesIV.2. Environmental factors predisposing to low urine volumeIV.2.1. Occupational risk of kidney stonesIV.2.2. Climate and temperature as risk factorsWater & recurrenceV. Prevention of stone recurrence with high water intakeV.1. Reduction of recurrence rate with increased water intakeV.2. Water intake and urinary parameters in stone formersWater & incidenceVI. Primary prevention of stones with high water intakeVI.1. Reduction of stone incidence with increased water intakeVI.2. Water intake and urinary parameters in healthy subjectsWater & health costsVII. Water intake and health costs of kidney stonesVII.1. Reduction of stone recurrence costs via adequate water intakeVII.2. Reduction of first stone costs with adequate water intakeRecommendationsVIII. Dietary and water recommendations for stone preventionVIII.1. Guidelines for the prevention of recurrence in patientsVIII.2. Dietary and water guidelines for general populationConclusion References
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Water & recurrence
Recurrence rate of kidney stone disease is high: 40 to 60% of stone formers will relapse within 5 years following a first episode (Ettinger 1979; Hosking et al. 1983; Sutherland et al. 1985). Current recommendations to prevent stone recurrence involve diet and lifestyle (Brenner and Rector 2008; Tiselius et al. 2001). A high water intake had been advised as a preventive measure for stone recurrence since the time of Hippocrates, and was for a long time the only advice given to reduce the risk (Borghi et al. 1999c; Ramello et al. 2000). Until a few decades ago, there was little scientific evidence of this preventive effect.
Prospective cohort studies have shown that recurrence was associated with lower urine volumes. In his study published in 2005, Daudon enrolled 181 stone formers who were advised to follow a particular diet (including a fluid intake sufficient to result in a urine volume of at least 2.0L/d). After a 3-years follow-up, 72 patients experienced at least one episode of recurrence while 109 subjects remained stone free. Urinary analysis showed that patients who remained stone free had increased their urine volume to a greater extent than patients who experienced recurrence: in stone-free patients, mean daily urine volume was 2.26L/d, as compared to 1.74 in patients with recurrence. Actually, a 1.0L/d increase in urine volume was associated with a hazard ratio of 0.32, meaning that an increase in fluid intake leads to a reduced risk of stone recurrence (Daudon 2005). Likewise, in a study involving 70 stone patients, 25 were treated with a calcium channel blocker, 25 increased their fluid intake to achieve a urine volume of at least 2.5L/d and 20 received no treatment. A reduction in recurrence from 55% to 40% was observed in subjects who increased their fluid intake as compared to no treatment group; however no information was given regarding mean fluid intake in subjects without any treatment (Sarica et al. 2006).
The main research regarding this matter was published by Borghi et al. in 1996. They assessed the causal effect of increased water intake and risk of kidney stone recurrence. Authors recruited 199 stone formers right after their first episode of kidney stones. Patients were randomized in two groups: in the first group, 99 patients increased their water intake to achieve a urine volume of at least 2.0L/d, while 100 subjects in the second group didn’t receive any particular instructions. After a 5-years follow-up, patients with higher water intake presented a significantly lower recurrence rate (12.1% compared to 27% in controls, p=0.008) (Borghi et al. 1996).
Studies performed on stone formers investigated the impacts of an increased urine volume on urinary parameters related to stone formation. Results showed that an increase in urine volume leads to a reduction of urine density (Amar et al. 2006), and urine supersaturation for calcium oxalate (Borghi et al. 1999a; Pak et al. 1980), calcium phosphate and monosodium urate (Pak et al. 1980). Moreover, increasing urine volume also leads to an increase of the upper limit of metastability for calcium oxalate (Pak et al. 1980), and to an increase of the permissible increment in oxalate, meaning that a greater level of supersaturation of these compounds is required to initiate crystallization (Borghi et al. 1999a). Furthermore, increased urine volume reduced the frequency of crystalluria (Amar et al. 2006; Kaid-Omar et al. 2001; Rodgers et al. 1991). Finally, increasing water intake leads to a higher rate of clearance of residual stone fragments (Sarica et al. 2006), and to better rates of spontaneous passage of stones (Kaid-Omar et al. 2001).
Take home messages
Increasing water intake is an effective measure to reduce the risk of kidney stone recurrence.