Magnesium in drinking water may influence Mg homeostais. Epidemiological studies have shown an increased mortality in heart infarction in areas with a low Mg content in the water. Against this background a study was undertaken, examining the relation between the blood pressure increase during pregnancy and the amount of Mg in drinking water. The study was performed on the island of Gotland in Sweden, where large variations in the Mg content in drinking water are present. Delivery records from 250 women were examined and the blood pressure at weeks 12-37 was recorded.

The increase in diastolic blood pressure between week 12 and the other weeks was significantly higher in communities with 30 mg Mg as compared to lower levels. Previous data on Mg and blood pressure do not support a conclusion that the observed differences represent causality. An accumulation of individuals with other risk factors is a more likely explanation, although no hypothesis regarding specific risk factors can be formulated. To elucidate this further research in terms of Mg loading tests should be performed.