Key result
Calcium supplementation resulted in a smaller reduction in systolic blood pressure by >5 mmHg between 2 and 6 hours and increased blood coagulability at 4 hours compared to placebo.
Why the study?
Does calcium supplementation acutely increase blood pressure and blood coagulation in post-menopausal women?
RCT (n=100)
Double-blind
Computer-generated variable-block schedule
No
Does calcium supplementation acutely increase blood pressure and blood coagulation in post-menopausal women?
Calcium supplementation in post-menopausal women acutely attenuates normal diurnal blood pressure reductions and increases blood coagulability, providing a potential mechanism for the increased cardiovascular risk associated with calcium supplements.
Warrants caution with calcium supplements in postmenopausal women; confirms acute BP and coagulability effects as potential CV risk mechanism.
Recent evidence suggests that Ca supplements increase the risk of cardiovascular events, but the mechanism(s) by which this occurs is uncertain. In a study primarily assessing the effects of various Ca supplements on blood Ca levels, we also investigated the effects of Ca supplements on blood pressure and their acute effects on blood coagulation. We randomised 100 post-menopausal women to 1 g/d of Ca or a placebo containing no Ca. Blood pressure was measured at baseline and every 2 h up to 8 h after their first dose and after 3 months of supplementation. Blood coagulation was measured by thromboelastography (TEG) in a subgroup of participants (n 40) up to 8 h only. Blood pressure declined over 8 h in both the groups, consistent with its normal diurnal rhythm. The reduction in systolic blood pressure was smaller in the Ca group compared with the control group by >5 mmHg between 2 and 6 h (P≤0·02), and the reduction in diastolic blood pressure was smaller at 2 h (between-groups difference 4·5 mmHg, P=0·004). Blood coagulability, assessed by TEG, increased from baseline over 8 h in the calcium citrate and control groups. At 4 h, the increase in the coagulation index was greater in the calcium citrate group compared with the control group (P=0·03), which appeared to be due to a greater reduction in the time to clot initiation. These data suggest that Ca supplements may acutely influence blood pressure and blood coagulation. Further investigation of this possibility is required.
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Bristow et al. (2015) conducted an RCT in Post-menopausal women (n=100). Calcium supplements vs. Placebo was evaluated on Change in systolic blood pressure from baseline between 2 and 6 hours (Difference >5 mmHg, p=≤0.02). Calcium supplementation resulted in a smaller reduction in systolic blood pressure by >5 mmHg between 2 and 6 hours and increased blood coagulability at 4 hours compared to placebo.
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