Bone Abstracts

Calcium supplements are associated with increased cardiovascular risk, but the mechanism by which this occurs is presently uncertain. In a secondary analysis of a trial examining the acute effects of calcium supplements, we found that blood pressure declined over 8 h in the control group, consistent with its diurnal rhythm, and that this decline was smaller in the calcium group [1]. To investigate these effects further, we carried out a randomised controlled cross-over trial of 40 healthy postmenopausal women. Women attended our clinic on two occasions at which they received a single dose of 1000 mg of calcium as citrate, or a placebo containing no calcium. Visits were separated by at least 7 days. Blood was sampled and blood pressure measured immediately before, and then 2, 4 and 6 h after, participants received each intervention. Ionised calcium increased from baseline after calcium citrate, and did not change after placebo. Blood pressure declined from baseline after calcium citrate and placebo. However, there was a significant difference between the changes in systolic blood pressure after calcium and placebo (ANOVA, P=0.02). The decline in systolic blood pressure from baseline was smaller after calcium compared with placebo by 4 mmHg at 2 h, 6 mmHg at 4 h and 9 mmHg at 6 h. A similar pattern was observed for diastolic blood pressure, although the differences were smaller (1–2 mmHg) and not significant. These findings confirm those of our previous trial, and suggest that in older adults the use of calcium supplements will result in blood pressures 4–9 mmHg higher in the 6 h after dosing. These changes in blood pressure, if repeated long-term, may contribute to the increased cardiovascular risk associated with calcium supplement use.

1. Bristow SM et al. (2015) Br J Nutr 114, 1868–1874.