The effect of a rechallenge with CaCO3 in patients who have been classified as responders to an initial challenge.

In a previous study 25 of 95 patients were identified as possibly having a fall in blood pressure with CaCO3 supplementation. After a 3-month period off calcium and on their usual diet, 12 of these were randomly assigned to receive placebo or CaCO3. Four crossed over to the alternate therapy after 2 months on the first agent. The change in blood pressure with placebo was 0.3 +/- 4.3/2.9 +/- 2.7 mmHg and the change in blood pressure with CaCO3 at 20 mmol/day was 1.3 +/- 4.8/-0.3 +/- 4.2 mmHg. These changes were not different from each other or from zero, and contrasted with the fall of 16.5 +/- 2.3/7.8 +/- 2.7 mmHg in the initial study. This study indicates that apparent individual falls in blood pressure with calcium supplementation need to be verified by rechallenge before such patients can be classified as responders. The absence of a predictable response, if applied to other studies, casts doubt on the conclusions made. Calcium supplementation cannot be recommended as a method of reducing blood pressure in people with mild hypertension.