Domestic Water Mineral Composition and Incident Glaucoma Risk: A Prospective Cohort Study From the UK Biobank

Purpose: To investigate the association between geographically assigned domestic water mineral composition and incident glaucoma in a large prospective cohort. Methods: This study included 434,112 UK Biobank participants without glaucoma at baseline. Exposures included domestic water hardness and concentrations of calcium, magnesium, and calcium carbonate. Incident glaucoma was identified through hospital inpatient records. Cox proportional hazards models were used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs), with adjustment for demographic, socioeconomic, lifestyle, and clinical covariates. Restricted cubic spline, subtype-specific, multiple imputation, proportional hazards, propensity score–matched, and biomarker analyses were conducted. Results: During a median follow-up of 14.07 years, 3125 participants developed glaucoma. For each standard deviation increase in mineral concentration, adjusted HRs were 1.10 (95% CI, 1.06–1.14) for calcium, 1.08 (95% CI, 1.05–1.12) for calcium carbonate, and 1.12 (95% CI, 1.08–1.15) for magnesium. Very hard water (>180 vs. <60 mg/L calcium carbonate, US Geological Survey classification) and hard water (≥200 vs. <200 mg/L, World Health Organization classification) were associated with higher glaucoma risk, with adjusted HRs of 1.23 (95% CI, 1.13–1.34) and 1.22 (95% CI, 1.13–1.31), respectively. Restricted cubic spline analyses showed nonlinear associations for all three mineral indicators. For calcium and calcium carbonate, HRs increased across low to intermediate concentrations and attenuated at higher concentrations. For magnesium, HRs increased gradually, mainly across low to intermediate concentrations. Estimates were consistent across sensitivity analyses. Conclusions: Geographically assigned domestic water mineral composition was associated with incident glaucoma, with distinct nonlinear patterns across mineral indicators. These observational findings require independent confirmation.