A randomized, double-blind, placebo-controlled crossover trial of oral
calcium supplementation was carried out in 18 patients with uncomplicated
essential hypertension. After 15 weeks of oral
calcium supplementation, 1 g/day, of the patients' habitual diet, the only blood pressure change (compared with the results of placebo treatment) was in the average standing systolic blood pressure, which was significantly reduced (-8.6 mm Hg; p less than 0.01). The 24-hour urinary
calcium excretion and the total serum
calcium concentration increased significantly during
calcium supplementation (p less than 0.05), indicating good compliance with the treatment. The individual blood pressure changes with high
calcium intake were found to be inversely related to basal 24-hour urinary
calcium excretion (r = -0.69, p less than 0.001 for standing systolic pressure; r = -0.55, p less than 0.002 for standing diastolic pressure). This correlation was independent of age, basal blood pressure, serum
calcium concentration, basal 24-hour urinary
sodium excretion, and
body weight changes during the trial. In particular, a subgroup of six patients, who had a basal 24-hour urinary
calcium excretion higher than the mean + 2 SD of a reference healthy population previously described, showed a substantial average blood pressure fall at variance with the other patients in the study. These results do not support the usefulness of an oral
calcium supplement in the majority of subjects with mild
essential hypertension; however, they suggest that a group of patients with a previously reported abnormality of
calcium metabolism may be responsive to this therapeutic measure.