Acute effects of calcium supplements on blood pressure and blood coagulation: secondary analysis of a randomised controlled trial in post-menopausal women

Br J Nutr. 2015 Dec 14;114(11):1868-74. doi: 10.1017/S0007114515003694. Epub 2015 Sep 30.


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.

Keywords: Blood coagulation; Blood pressure; Calcium supplements; Randomised trials; TEG thromboelastography.

Publication types

  • Comparative Study
  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aged
  • Aged, 80 and over
  • Blood Coagulation
  • Blood Coagulation Disorders / epidemiology
  • Blood Coagulation Disorders / etiology*
  • Blood Pressure
  • Bone Density Conservation Agents / administration & dosage
  • Bone Density Conservation Agents / adverse effects*
  • Bone Density Conservation Agents / therapeutic use
  • Calcium Carbonate / adverse effects
  • Calcium Carbonate / therapeutic use
  • Calcium Citrate / adverse effects*
  • Calcium Citrate / therapeutic use
  • Calcium, Dietary / administration & dosage
  • Calcium, Dietary / adverse effects*
  • Calcium, Dietary / therapeutic use
  • Cohort Studies
  • Dietary Supplements / adverse effects*
  • Double-Blind Method
  • Durapatite / adverse effects
  • Durapatite / therapeutic use
  • Elder Nutritional Physiological Phenomena*
  • Female
  • Humans
  • Hypertension / epidemiology
  • Hypertension / etiology*
  • Middle Aged
  • New Zealand / epidemiology
  • Osteoporosis, Postmenopausal / epidemiology
  • Osteoporosis, Postmenopausal / prevention & control
  • Patient Dropouts
  • Risk


  • Bone Density Conservation Agents
  • Calcium, Dietary
  • Durapatite
  • Calcium Carbonate
  • Calcium Citrate

Associated data

  • ANZCTR/ACTRN12611000232932