Ecologic study of water hardness and cerebrovascular mortality in Japan.

Elevated levels of water hardness have been associated with reduced mortality from cardiovascular and cerebrovascular diseases. In this ecologic study, the authors examined the relationship between water hardness and cerebrovascular mortality in the 44 municipalities of Osaka Prefecture, Japan. Data on cerebrovascular death rates and water hardness in each municipality were obtained from public records; information on socioeconomic and health-care status in each municipality was incorporated with multiple logistic-regression analysis. The authors were unable to substantiate an inverse association of water hardness with cerebrovascular mortality--although the adjusted odds ratio in which the highest vs. lowest tertiles of water hardness were compared was 0.90 (95% confidence interval = 0.79, 1.02) in females. In addition, the difference between the sexes was not significant. In summary, the authors found no evidence that water hardness protected against cerebrovascular mortality.