Insufficient intake of water and other liquids, i.e. permanent dehydration, even if slight, surely increases the risk for urolithiasis of all types. Urolithiasis is the formation of urinary calculi or stones in the bladder or urinary tract. On the other hand, qualitative assessment shows that the content of water minerals, more precisely of magnesium and calcium, plays a less important role. Urinary stone formation is a process involving multiple factors, i.e. not only intake of liquids, but also genetic predisposition, eating habits, climatic and social conditions, gender, etc.
Several studies documented that higher water hardness is associated with higher incidence of urolithiasis among the population supplied with such water. However, more studies found softer water to be associated with a higher risk for urolithiasis. Nevertheless, most recent epidemiological studies explain these controversial results by differences in the study designs and say that water hardness ranging between the values commonly reported for drinking water is not a significant factor in urolithiasis (Singh et al, 1993; Ripa et al, 1995; Kohri et al, 1993; Kohri et al, 1989).
Any correlation between water hardness, or the drinking water calcium or 14 magnesium level, and the incidence of urolithiasis was not found in the last vast USA epidemiological study with 3270 patients (Schwartz et al, 2002). The quoted Japanese studies did not find that the water calcium or magnesium levels alone had an effect on the incidence of urolithiasis but did find that the Mg to Ca ratio had: one study reported the lower Mg to Ca ratio to be associated with a higher risk for urolithiasis regardless of type and the incidence of urolithiasis to correlate with the type of geological subsoil. (Kohri et al, 1989) Another study found a correlation between the higher Mg to Ca ratio and higher incidence of infectious phosphate urolithiasis (Kohri et al, 1993).
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Many experimental studies document that higher water hardness does not pose any risk for urolithiasis (which is not true of extreme water hardness beyond the range to be considered for drinking water - see below) and confirm concordantly that intake of calcium-rich water (or magnesium-rich water) reduces the risk for calcium oxalate urolithiasis (Rodgers, 1997; Rodgers, 1998; Caudarella et al, 1998; Marangella et al, 1996; Gutenbrunner et al, 1989; Ackermann et al, 1988; Sommariva et al, 1987). Intake of such water is associated with higher urinary calcium elimination and at the same time with lower urinary oxalate elimination probably due to oxalate bond to calcium in the intestine with subsequent prevention of oxalate absorption and enhanced oxalate elimination through feces.
Nevertheless, these conclusions do not apply to patients after urinary stone removal. Isolated experiments suggested that intake of softer drinking water resulted in a lower rate of recurrent urolithiasis (Bellizzi et al, 1999; Coen et al, 2001; Di Silverio et al, 2000) but admitted at the same time that the results could not be generalized and depended on multiple factors, e.g. whether water was given between meals as in one of the studies above or during meals when, in contrast, harder water intake may have been associated with a lower rate of recurrences (Bellizzi et al, 1999). Genetic predispositions and eating habits may play a relevant role in this regard. High hardness (>5 mmol/l), which is not typical of drinking water, may be associated with a higher risk for urinary and salivary stone formation as documented by a Russian epidemiological study (Mudryi, 1999).
The author says that a long-term intake of drinking water harder than 5 mmol/l results in a higher local blood supply in the kidneys and subsequent adaptation of the filtration and resorption processes in the kidney. This is believed to be a protective reaction of the human body, which may lead, if the conditions persist, to alteration of the body's regulatory system with possible subsequent development of urolithiasis and hypertension. The risk for urolithiasis was also associated with intake of water with a hardness of 10.5 mmol/l (Ca 370 mg/l) as documented by the already quoted Italian study (Coen et al, 2001). No evidence is available to document harm to human health from harder drinking water.
Perhaps only a high magnesium content (hundreds of mg/l) coupled with a high sulphate content may cause diarrhea. Nevertheless, such cases are rather rare; other harmful health effects due to high water hardness (e.g. the effects on the eliminatory system as mentioned above) were observed in waters rich in dissolved solids (above 1000 mg/l) showing mineral levels, which are not typical of most drinking waters. In the areas of the Tula region supplied with drinking water harder than 5 mmol/l, higher incidence rates of cholelithiasis, urolithiasis, arthrosis and arthropathies as compared with those supplied with softer water were reported (Muzalevskaya et al, 1993). Another epidemiological study carried out in the Tambov region found hard water (more than 4-5 mmol/l) to be a possible cause of higher incidence rates of some diseases including cancer (Golubev et al, 1994). The results of the studies concerning the relationship between water hardness and tumors are discordant, but most of them are supportive of the protective effect of harder water.
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