Studies of water quality and cardiovascular disease in the United Kingdom.

The British Regional Heart Study aims at determining factors responsible for the marked regional variations in cardiovascular disease in Great Britain. PHASE I is a retrospective study of cardiovascular mortality with water quality (hardness and more than 20 other water parameters have been studied), climate, air pollution, socio-economic and genetic factors. An association between water hardness and cardiovascular mortality is reaffirmed, towns with soft water tending to have higher death rates than towns with hard water. This relationship is somewhat weakened after allowing for climatic and socio-economic factors but remains statistically significant for both coronary heart disease and stroke. After adjustment for other factors, soft water areas (around 0.25 mmol/l) have a 10-15% higher cardiovascular mortality that areas of medium hardness (around 1.70 mmol/l) whereas any further increase beyond 1.70 mmol/l has little extra lowering effect on cardiovascular mortality.