FOR MORE than 20 years, investigators have studied water hardness and cardiovascular disease (CVD) mortality.1 Despite studies from several countries having yielded conflicting results,2 recommendations have been made urging caution about softening drinking water, as though there were a simple and constant linear relationship between water softness and CVD mortality.3 This discussion should make it clear why a simple linear hypothesis explaining these findings, eg, water hardness, per se, protects against heart disease, is untenable and probably incorrect.
Numerous reviews have cited Schroeder's4 findings regarding water hardness and heart disease mortality, but they have rarely mentioned the correlations of water hardness with several other mortality categories in this same article. Schroeder reported significant negative correlations of water hardness with CVD mortality, cancer mortality, cirrhosis of the liver, population density, and percent nonwhite population. Conversely, he reported significant positive correlations of water hardness with motor
Hammer DI, Heyden S. Water Hardness and Cardiovascular Mortality: An Idea That Has Served Its Purpose. JAMA. 1980;243(23):2399–2400. doi:10.1001/jama.1980.03300490017018
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