Influence of a mineral water rich in calcium, magnesium and bicarbonate on urine composition and the risk of calcium oxalate crystallization.

Objective: To evaluate the effect of a mineral water rich in magnesium (337 mg/l), calcium (232 mg/l) and bicarbonate (3388 mg/l) on urine composition and the risk of calcium oxalate crystallization.
Design: A total of 12 healthy male volunteers participated in the study. During the baseline phase, subjects collected two 24-h urine samples while on their usual diet. Throughout the control and test phases, lasting 5 days each, the subjects received a standardized diet calculated according to the recommendations. During the control phase, subjects consumed 1.4 l/day of a neutral fruit tea, which was replaced by an equal volume of a mineral water during the test phase. On the follow-up phase, subjects continued to drink 1.4 l/day of the mineral water on their usual diet and collected 24-h urine samples weekly.
Results: During the intake of mineral water, urinary pH, magnesium and citrate excretion increased significantly on both standardized and normal dietary conditions. The mineral water led to a significant increase in urinary calcium excretion only on the standardized diet, and to a significantly higher urinary volume and decreased supersaturation with calcium oxalate only on the usual diet.
Conclusions: The magnesium and bicarbonate content of the mineral water resulted in favorable changes in urinary pH, magnesium and citrate excretion, inhibitors of calcium oxalate stone formation, counterbalancing increased calcium excretion. Since urinary oxalate excretion did not diminish, further studies are necessary to evaluate whether the ingestion of calcium-rich mineral water with, rather than between, meals may complex oxalate in the gut thus limiting intestinal absorption and urinary excretion of calcium and oxalate.