Fifteen patients with uncomplicated mild to moderate
primary hypertension (7 males, 8 females, age range 36-65 years) were submitted to a double blind randomized crossover study, receiving MgO 3 times a day at a daily dose of 1.0 g (600 mg/day of
magnesium) and placebo for a period of 6 weeks. This was to test the effects of oral
magnesium supplementation on blood pressure and
sodium,
potassium,
calcium and
magnesium intraerythrocyte concentrations. Concomitantly, plasma
renin activity and serum
aldosterone was also measured. Oral
magnesium reduced significantly the systolic (delta = -7.6 mmHg, P < 0.05); diastolic (delta = -3.8 mmHg, P < 0.01) and mean blood pressure (delta = -5.9 mmHg, P < 0.01). After
magnesium supplementation intraerythrocyte
sodium concentration was reduced (delta = -0.55 mEq/l per cell, P < 0.01) and intraerythrocyte
magnesium concentration was increased (delta = 1.20 mg/dl per cell, P < 0.01). The diminution of the blood pressure correlated positively with the reduction in intraerythrocyte
sodium (r = 0.66, P < 0.01) after
magnesium. However, our results have shown that the blood pressure response to oral
magnesium was not homogeneous. Forty percent of our patients had their blood pressure effectively controlled (more than 10 mmHg reduction in mean blood pressure), being the hypotensive effect more evident in patients with recent
hypertension and in those where the reduction in intraerythrocyte
sodium was significantly greater than in the non-responder individuals. Intraerythrocyte
potassium and
calcium, serum
aldosterone, plasma
renin activity and urinary
sodium excretion were maintained unchanged after
magnesium supplementation. These data showed that oral
magnesium supplementation may reduce the blood pressure, which can be partially explained by the decrease in intracellular
sodium and augment in intracellular
magnesium.