Cardiovascular mortality and calcium and magnesium in drinking water: an ecological study in elderly people

Previous studies found relations between cardiovascular mortality and minerals in drinking water, but the major works considered water hardness or neglected the differences between adults and elderly. Drinking water is an important source of calcium in the elderly particularly because of increased needs and decreased consumption of dairy products.

We collected informations about all deaths (14,311) occurring in 69 parishes of the South-West of France during 7 years (1990-1996). We obtained the causes of deaths from a special service of INSERM for each death, with age at death and sex. The exposure value was supplied by administrative source (DDASS) and by measurement surveys. We use an extra-Poisson variation model to take into account the heterogeneity of the population of these parishes.

A significant relationship was observed between calcium and cardiovascular mortality with a RR: 0.90 for non-cerebrovascular causes and RR: 0.86 for cerebrovascular (when calcium is higher than the second tercile: 94 mg/l). We found a protective effect of magnesium concentrations between 4 and 11 mg/l with a RR: 0.92 for non-cerebrovascular and RR: 0.77 for cerebrovascular mortality, as compared to concentrations lower than 4 mg/l.

These findings strongly suggest a potential protective dose-effect relation between calcium in drinking water and cardiovascular causes. For magnesium, a U-shape effect is possible, especially for cerebrovascular mortality.