Correlation Between Heart Disease and the Hardness of Drinking Water

Abstract

This study investigates the possible correlation between heart disease mortality and the hardness of drinking water to determine if there are protective factors associated with hard water that may reduce heart disease. The study attempts to see if such a correlation can be found in the population that is supplied by 31 public water treatment plants spread across 17 counties in Ohio. The 31 public water treatment plants, which maintain a hardness with little variance from year to year, serve an estimated total 2,658,000 customers, about 25% of the total population of Ohio. Surface-water supplies 69% of the population, groundwater 30% and 1% is supplied by a mixture of surface-water and groundwater. The total hardness, expressed in mg/l CaCO₃, of the study area ranges from an annual average of 93 mg/l to 448 mg/l. To test for a correlation, total hardness data is acquired on the drinking water supplied by the water treatment plants and is compared to heart disease mortality data, for the year 2007, obtained from the Ohio Department of Health, Center for Public Health Statistics and Information. Analysis shows that a positive correlation of 0.427 exists, with changes in total water hardness accounting for 18.3% of the variance found in heart disease mortality rate. An age adjusted analysis, for individuals over 35 years of age also resulted in a positive correlation with total water hardness accounting for 15.4% of the variance in heart disease mortality. In order to eliminate possible confounding factors from the study, 16 additional examinations were done on the original data; all but three resulted in positive correlations.