The association between domestic water hardness and kidney stone disease: a prospective cohort study from the UK Biobank.
Level 3 - non-randomized controlled study
Prospective cohort study
PubMed 39784501 · doi:10.1097/JS9.0000000000002198
What was done
Prospective cohort study analyzing 288,041 UK Biobank participants without a prior history of kidney stones followed from 2006 to 2024. Exposures were domestic water hardness, calcium, calcium carbonate, and magnesium concentrations. Cox proportional hazards models adjusted for age, sex, ethnicity, economic level, education, Townsend Deprivation Index, Index of Multiple Deprivation, assessment center, BMI, medications influencing calcium and magnesium metabolism, and water intake.
What was found
Over follow-up, 3,298 participants (1.14%) developed kidney stones. Mean water concentrations were 52.61 mg/L calcium, 135.01 mg/L calcium carbonate, and 4.66 mg/L magnesium. Higher magnesium levels (Q4, >5 mg/L) were associated with lower stone risk (HR 0.88, 95% CI 0.80-0.97). Domestic water hardness, calcium, and calcium carbonate had no significant association in the overall cohort. In subgroup analyses, hard water and high calcium increased risk by 18% to 34% in participants over 60 years old and females. High magnesium (>5 mg/L) decreased risk by 10% to 28% in males, participants 45 years old or younger, and those without renal failure. Magnesium protection was stronger with hard water (HR 0.73, 95% CI 0.61-0.87), high calcium carbonate (HR 0.62, 95% CI 0.50-0.78), and high calcium (HR 0.48, 95% CI 0.33-0.71).
Why it matters
This study clarifies conflicting evidence on drinking water minerals, demonstrating that water magnesium has a protective effect against kidney stones, particularly in hard-water areas, while calcium-rich hard water may selectively elevate risk in older adults and females.
Limits
Observational design subject to residual confounding. Exposure was estimated from domestic water supplies rather than measured individual fluid consumption, filtration use, or dietary mineral intake. Stone composition types were not reported 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.