It is thus likely that the 1988 analysis also reflected the magnesium and calcium content over the time from which the mortality data were obtained. The results from the study reconfirm the previously observed inverse relationships between mortality from cardiovascular disease and water hardness. The hypothesis that toxic materials in drinking water can be related to cardiovascular mortality could not be tested in this study, as significant amounts of lead or cadmium were not found in the water of the municipalities examined. The results demonstrated a statistically significant relationship between the amount of magnesium and ischemic heart disease but not cerebrovascular disease. The possible importance of confounding factors must be considered.
Cardiovascular disease is more common in built-up areas.
However the populations of the municipalities ranged in size between about 8000 and 100000, and there was no relationship between population size and mortality from ischemic heart disease or cerebrovascular disease. Magnesium in the drinking water showed a tendency towards lower levels in municipalities in the north of Sweden, but this geographic distribution was not uniform. Smoking habits represent an important possible confounder, but a covariation between the extent of smoking in different municipalities and the magnesium content of the water is not likely. The relation between ischemic heart disease in men and water magnesium levels illustrated in figure 1 is probably complex. For the municipalities with low levels of magnesium in the water, both high and low mortality could be found.