Associations between domestic water hardness and risk of experiencing 15 different cardiovascular events: a prospective cohort study of 324,136 United Kingdom Biobank participants.

BACKGROUND

Previous studies have demonstrated domestic water hardness (DWH)-cardiovascular disease (CVD) associations, but the results are inconsistent, and investigations of specific CVD subtypes are scarce.

OBJECTIVES

We aimed to investigate the individual and combined associations of DWH with CVD and its subtypes.

METHODS

This cohort study included United Kingdom Biobank participants whose address codes were used to obtain DWH data [calcium carbonate (CaCO3), calcium (Ca), and magnesium (Mg)] from water supply companies. Incident CVD events were identified via International Classification of Diseases-10th Revision codes. The individual and combined associations between DWH exposure and incident CVD events were evaluated via Cox proportional hazards regression and quantile G-computation, respectively.

RESULTS

During a median follow-up period of over 13.41 y, 5780 CVD deaths and 60,184 CVD cases were identified among 324,136 participants (mean ± standard deviation age=55.76 ± 8.08 y; female proportion = 53.95%). U-shaped associations were observed between CaCO3 and CVD death (P-nonlinear = 0.024) and between Ca and CVD (P-nonlinear = 0.008). Each log-transformed Mg interquartile range increase was associated with decreased CVD risk [hazard ratio (HR) = 0.978; 95% confidence interval (CI) = 0.961, 0.996]. DWH was linearly and nonlinearly associated with 7 CVD subtypes (chronic rheumatic heart diseases, ischemic heart diseases, nonrheumatic valve disease, myocarditis and cardiomyopathy, arrhythmias, heart failure, and cerebral infarction). Combined DWH exposure was associated with increased chronic rheumatic heart disease risk (HR = 1.070; 95% CI: 1.011, 1.133), with Mg having the largest negative weight of 1.000 and Ca having the largest positive weight of 0.908.

CONCLUSIONS

DWH was associated with cardiovascular health, including 9 CVD events. Specifically, higher concentrations of Mg and moderate levels of CaCO3 and Ca were associated with lower CVD risk. Combined DWH was associated with increased chronic rheumatic heart disease risk.