The Inconsistent Effects of Calcium Supplements upon Blood Pressure in Primary Hypertension

The effects of 800mg of elemental calcium per day (calcium carbonate or calcium citrate) on blood pressure were compared with a placebo in a controlled randomized, crossover, double-blinded trial involving 26 patients with uncomplicated primary hypertension. Each patient took two of the three forms of therapy orally for 8-week intervals with a 2-week washout period in between. Standing mean blood pressure rose an average of 5.7mm Hg on placebo, rose an average of 0.5mm Hg on calcium carbonate, and fell an average of 2.2mm Hg on calcium citrate. Changes in sitting mean pressures averaged +1.9mm Hg on placebo, -0.4mm Hg on calcium carbonate, and -0.4mm Hg on calcium citrate. Some patients had a fall, others had a rise in blood pressure on each form of calcium. Similarly, inconsistent responses were noted among the nine patients who took both forms of calcium. Neither initial nor post treatment biochemical measures nor patient characteristics were predictive of the blood pressure response. Combinations of various measures and characteristics analyzed by the multiple regression technique explained only 30% of the overall variability in blood pressure. Therefore, until ways can be found to predict the response, calcium supplements should not be routinely prescribed for the treatment of hypertension and, if given for any indication, blood pressure should be monitored.