Effects of water hardness on urinary risk factors for kidney stones in patients with idiopathic nephrolithiasis.
Level 2 - randomized trial
Individual randomized crossover trial
PubMed 9873217 · doi:10.1159/000046301
What was done
Eighteen patients with idiopathic nephrolithiasis on a standardized dietary calcium intake (800 mg/day) were evaluated in a double-blind, randomized crossover trial. Participants consumed 2 liters per day between meals of baseline tap water for 1 week, followed by 1-week periods drinking bottled hard water (calcium 255 mg/l) or soft water (calcium 22 mg/l, Fiuggi water). Urinary concentrations of calcium, oxalate, and citrate were measured.
What was found
Compared to both tap and soft water, hard water ingestion resulted in a significant 50% increase in urinary calcium concentration, while oxalate excretion showed no changes. The calcium-citrate index showed a significant threefold increase during hard water ingestion compared to soft water ingestion.
Why it matters
The study suggests that consuming soft drinking water between meals rather than hard water decreases urinary calcium and improves the calcium-citrate index, potentially reducing the risk of calcium stone recurrence.
Limits
The study had a very small sample size (18 patients) and short intervention periods (1 week per phase). Hard stone recurrence endpoints were not measured directly, and baseline tap water composition was not detailed in the abstract.
Cited by
- contradicts Drinking hard water containing calcium and magnesium is associated with lower incidence of kidney stone formation compared to consuming softened water.