Relationship between 'sudden' coronary deaths and drinking water hardness in five Yorkshire cities and towns.

The incidence of sudden coronary deaths verified by autopsy on 1004 males aged 35-64 years in the years 1974-75 in 5 Yorkshire cities or towns was found to be unrelated to the total hardness or magnesium content of the drinking water. However, within a single community (Leeds Metropolitan area) there was a crude inverse relationship between the sudden death risk in the population and the hardness and magnesium content of the drinking water. During the same period there was a generally inverse relationship between both total water hardness and magnesium content and notified deaths from coronary heart disease. The reason for this difference in the distribution of deaths notified as of coronary origin and those proven by autopsy is unknown.