Effect of water composition and timing of ingestion on urinary lithogenic profile in healthy volunteers: a randomized crossover trial

Kidney stone disease is a common condition with a high recurrence rate and elevated costs. Despite the well-known positive effects of high fluid intake, there are little data about the roles of water composition and timing of ingestion during the day. This study examines the effect of two different waters [calcium-bicarbonate water (CBW) and oligomineral water (OW)] consumed at different times during the day on urine composition in a group of healthy volunteers. In a cross-over randomized trial, 12 healthy volunteers were assigned to a different sequence of four combined interventions (1 L of water consumed during fasting and 1 L of water consumed with meals): CBW/OW; OW/CBW; CBW/CBW; OW/OW. Participants were instructed to follow the same diet and to avoid smoking, caffeine and other beverages during the day of intervention, and to collect their urine every 2 h during the day, followed by a single overnight collection. The relative supersaturation for calcium oxalate was higher for CBW/CBW compared with all other interventions, while relative supersaturation for calcium phosphate was lower for the combination OW/CBW with meals. Urinary excretion of oxalate was lower in all interventions including CBW, while no significant differences were found for urinary calcium. Water composition and timing of ingestion have complex and interacting effects on lithogenic risk. Depending on individual characteristics, a strategy involving either OW or a mix of CBW during meals and OW outside of meals could be effective in modulating the lithogenic profile. Trial registered at clinicaltrial.gov: Protocol ID NCT03447847.