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 & incidence
Increased water intake is widely recommended for secondary prevention of urolithiasis but only a few investigations have focused on primary prevention.
Two prospective cohort studies involving 45,619 men and 91,731 women without any history of kidney stones showed an inverse correlation between fluid intake and the risk of nephrolithiasis. Relative risk for the highest quintile of fluid intake compared to the lowest quintile was 0.71 in men, and 0.61 in women. These results show that a higher fluid intake is associated with a lower risk of kidney stones (Curhan et al. 1993; Curhan et al. 1997b).
The strongest evidence of primary prevention with increased water intake was an interventional study published by Frank et al. in 1966. In this research, authors investigated the effect of a drinking education on urinary output and on the incidence of urolithiasis. Subjects with no history of kidney stones were enrolled in two towns of an arid desert mountain region of Israel. In the newly established town of Arad, subjects received education to high fluid intake, whereas settlers of the neighboring town of Beersheba constituted a control group with no instruction. After a three years follow up, a higher urine output and lower prevalence of urolithiasis existed in the educated citizens of Arad (prevalence of 0.28% in Arad and 0.85% in Bersheeba). This study shows that higher fluid intake achieved by education can prevent urolithiasis in a hot and dry climate (Frank and De 1966).
Only few studies have investigated the impact of increased water intake on urinary parameters involved in the process of stone formation. Most of these studies included healthy subjects as well as stone formers, and thus present evidence of a beneficial effect of increased water intake both for secondary and primary prevention of urolithiasis. For instance, Borghi et al. observed a beneficial effect of an increased fluid intake on several urinary risk factors in 12 healthy subjects. An additional intake of 500mL before going to bed led to a reduction of calcium oxalate (CaOx) relative supersaturation, and to an increase in the tolerance of oxalate without any modification of the metastability limit for CaOx. Besides, the inhibitory effect of macromolecules on CaOx crystallization was not altered by increased water intake (Borghi et al. 1999a). Similar results were reported by Pak et al. on 3 subjects with no history of kidney stones: increased water intake to achieve total water intake of 2.3, 2.5, 3.3L/d led to a reduction of urine supersaturation for calcium oxalate, calcium phosphate and monosodium urate, and to an increase of the upper limit of metastability for CaOx (Pak et al. 1980). More recently, De La Guéronnière et al. studied the effect of an increased water intake on the Tiselius Cristallization Risk Index (CRIT). Forty-eight healthy subjects were divided in a control and a water group, which was asked to drink a 2L/d additional water intake. After a week of intervention, subjects in the water group had increased their urine volume by 1.3L/d. In 24 hour urine, the CRIT was reduced by 33.9% in women and 44.8% in men as compared to controls (de La Gueronniere et al. 2011).
Take home messages
There is growing evidence that increasing water intake may help prevent first episodes of kidney stones.