[Drinking water hardness and chronic degenerative diseases. I. Analysis of epidemiological research].

For many years a causal relation between drinking water hardness and cardiovascular or other chronic degenerative diseases in humans has been hypothesized. In order to evaluate the association between the concentration of minerals (calcium and magnesium) responsible for the hardness of drinking water and human health, a review of all the articles published on the subject from 1980 up to today has been carried out. The retrieved articles have been divided into 4 categories: geographic correlation studies, cross-sectional studies, case-control and cohort studies, and clinical trials. The methods for the selection of the articles and the extraction and analysis of the data are detailed in this paper. Epidemiological studies have been reviewed critically, and some conclusions have been drawn taking into account the research in basic sciences and experimental studies. However, a formal meta-analysis has not been performed, due to the heterogeneity of measures of effect among the different studies.