Can calcium or magnesium supplements lower blood pressure when it is slightly elevated?

Details

Phase I of the Trials of Hypertension Prevention (TOHP) was a randomized, multicenter investigation that included double-blind, placebo-controlled testing of calcium and magnesium supplements. It involved 698 healthy adults aged 30 to 54 years with high-normal diastolic blood pressure (DBP), defined as 80 to 89 mm Hg; 10.5% were Black and 31% were women.

Participants received daily doses of 1 g of calcium as calcium carbonate, 360 mg of magnesium as magnesium diglycine, or placebos. Adherence was very high: 94 to 96% by pill counts. For the active supplements, significant net increases in all urine and serum adherence measures in white men, and in urine adherence measures in white women, corroborated this adherence.

Overall, neither calcium nor magnesium produced significant changes in blood pressure at 3 and 6 months. Analyses stratified by baseline calcium, magnesium, or sodium intake, or by initial blood pressure, also showed no effect of supplementation.

These analyses suggested that calcium supplementation may have decreased DBP in white women. Possible modifiers of the response in this subgroup included lower initial urinary calcium levels, urinary sodium levels, or lower body mass index.

However, the overall analyses indicated that calcium and magnesium supplements are unlikely to lower blood pressure in adults with high-normal DBP. The subgroup analyses are useful for generating hypotheses and raise the possibility of a benefit in white women, but that possibility requires testing in future trials.