Relationship of diuretic therapy and serum magnesium levels among participants in the Multiple Risk Factor Intervention Trial.

Abstract

Thiazide-like diuretics cause an increased excretion of magnesium in the urine. Low serum and selected tissue magnesium levels have been reported among diuretic users. Low magnesium levels have been associated with cardiac arrhythmias, neuromuscular changes, and increases in lipoprotein levels. The dietary intake of magnesium is borderline compared with the recommended dietary allowances. Water sources may therefore play an important role. Hard water contains more magnesium than soft water. The authors studied serum magnesium levels among special intervention Multiple Risk Factor Intervention Trial participants in two centers: Pittsburgh, Pennsylvania and Davis, California. These participants were men aged 35-57 years at entry to the trial in 1972-1974; the blood samples were obtained primarily in 1980-1981. Diuretic users primarily of chlorthalidone had an average 1 ppm lower serum magnesium level than nondiuretic users. About 15% of diuretic users had persistently lower magnesium levels on two samples approximately four months apart. The serum magnesium level was not correlated with the serum potassium level. This study is the first long-term follow-up of a well-defined group of hypertensives taking thiazide-like diuretics versus suitable controls. The results suggest that within similar populations, low serum magnesium levels are relatively rare even in the absence of supplementation with magnesium. Specific high-risk populations may exist in which a combination of diuretic therapy and low intake may contribute to magnesium deficiency. Further epidemiologic studies should include monitoring both serum and intracellular levels of magnesium among these potential high-risk groups on diuretic therapy. This approach may offer the best method of testing the relationship between water hardness, minerals, and cardiovascular disease.