Lack of association between water hardness and coronary heart disease mortality in Japan

BACKGROUND: Elevated levels of water hardness are related to lower mortality from coronary heart disease (CHD) in different populations. This ecologic study assessed whether water hardness is related to lower mortality from CHD in Osaka Prefecture, with 44 municipalities, Japan. METHODS: The mortality rate from CHD per municipality was calculated based on the number of coronary deaths and midyear population in 1995. Values for water hardness in each of the municipalities were estimated based on the yearly amount of water supply per source and the yearly average of water hardness for each source in 1997. Multiple logistic regression analysis was used to control socioeconomic status and health care status in each municipality. RESULTS: In males, after adjustment for age, an inverse dose-response relationship between water hardness and mortality from CHD was significant (P for linear trend=0.004). However, this relationship virtually disappeared after further adjusting for socioeconomic status and health care status. In females, there was no material association between water hardness and coronary mortality. CONCLUSIONS: This study provides no evidence that water hardness is preventive against mortality from CHD in Japan.