Review of epidemiological studies on drinking water hardness and cardiovascular diseases.

BACKGROUND Major risk factors do not entirely explain the worldwide variability of morbidity and mortality due to cardiovascular disease. Environmental exposures, including drinking water minerals may affect cardiovascular disease risks. METHOD We conducted a qualitative review of the epidemiological studies of cardiovascular disease and drinking water hardness and calcium and magnesium levels. RESULTS Many but not all ecological studies found an inverse (i.e., protective) association between cardiovascular disease mortality and water hardness, calcium, or magnesium levels; but results are not consistent. Some case-control studies and one cohort study found either a reduced cardiovascular disease mortality risk with increased drinking water magnesium levels or an increased risk with low magnesium levels. However, the analytical studies provide little evidence that cardiovascular risks are associated with drinking water hardness or calcium levels. CONCLUSION Information from epidemiological and other studies supports the hypothesis that a low intake of magnesium may increase the risk of dying from, and possibly developing, cardiovascular disease or stroke. Thus, not removing magnesium from drinking water, or in certain situations increasing the magnesium intake from water, may be beneficial, especially for populations with an insufficient dietary intake of the mineral.