Association Between Domestic Water Hardness and MRI-Based Measures of Brain Volume: Evidence from the UK Biobank

Background: While water hardness is a known factor in cardiovascular health, its influence on brain structure is not well understood. This study aimed to investigate the association between water hardness and brain volume. Methods: This prospective cohort study was performed with data from the UK Biobank. To assess the associations between water hardness and standardized volumes of total brain volume (TBV), white matter, and gray matter, generalized linear models were utilized. Potential nonlinear association between water hardness and brain volume were indicated by restricted cubic splines. Results: Compared with soft water (0 to 60 mg/l), hard water (>180 mg/l) correlated with reduced TBV (β: −0.06, 95% confidence interval [CI]: −0.09 to −0.04), white matter (β: −0.07, 95% CI: −0.09 to −0.04), and gray matter (β: −0.04, 95% CI: −0.06 to −0.02), with all P < 0.001. Restricted cubic spline analysis revealed linear relationships between water hardness and TBV. Conclusions: Elevated water hardness is associated with reduced brain volume. These findings suggest that optimizing drinking water mineral content might be a strategy for neuroprotection.