Calcium and magnesium in drinking water and the risk of death from hypertension.

Many studies have demonstrated a negative association between blood pressure and calcium and magnesium levels. This report examines whether calcium and magnesium in drinking water are protective against hypertension. All eligible hypertension deaths (2336 cases) of Taiwan residents from 1990 through 1994 were compared with deaths from other causes (2336 controls), and the levels of calcium and magnesium in the drinking water of these residents were determined. Data on calcium and magnesium levels in drinking water throughout Taiwan have been obtained from the Taiwan Water Supply Corporation. The control group consisted of people who died from other causes and the controls were pair matched to the cases by sex, year of birth, and year of death. Magnesium levels in drinking water were inversely related to the risk of death from hypertension. The adjusted odds ratios (95% confidence interval) for the highest versus lowest quintiles of exposure was 0.63 (0.47 to 0.84). After adjustment for magnesium levels in drinking water, there was no difference between the groups with different levels of calcium. The results of the present study show that there is a significant protective effect of magnesium intake from drinking water on the risk of hypertension. This is an important finding for the Taiwan water industry and human health.