Fig. 1Forest plots showing the relationships between serum calcium at baseline and subsequent cardiovascular events over a weighted mean follow-up period of 12.4 years. Only studies reporting a linear relationship are included. Data are shown separately for odds and hazard ratios, which are expressed per standard deviation of serum calcium. 95% confidence intervals (CIs) are shown. The result of each meta-analysis is shown as a diamond. Adapted from Reid et al., with permission from John Wiley and Sons [1]. MI, myocardial infarction; CHD, coronary heart disease.
Fig. 2Effects of calcium supplements on serum total calcium concentration in normal postmenopausal women. (A) The calcaemic effects of calcium (500 mg) as citrate administered fasting (closed circles) are contrasted with those of a dairy product meal with the same calcium content. (B) The calcaemic effects of calcium (500 mg) as citrate are contrasted when administered fasting (closed circles) or with a meal (open circles). (C) The calcaemic effects of 1 g calcium as citrate is shown at baseline in calcium-naive women (closed circles) or after 3 months of daily use of a 1 g calcium supplement (open circles). Adapted from Bristow et al., with permission from Cambridge University Press [3436]. aSignificantly different from citrate-fasting (P<0.05).
Fig. 3Kaplan-Meier survival curves for time to incident myocardial infarction or stroke by treatment allocation in a meta-analysis of patient-level data from five trials of calcium supplements used as monotherapy (n=8,151) (A, B), and calcium-naive women in the Women's Health Initiative (WHI) calcium and vitamin D trial (n=16,718) (C, D). The magnitude and time-course of the effects of calcium supplements on the two groups of vascular events were very similar in these independent databases. Adapted from Radford et al. [44]. HR, hazard ratio; CI, confidence interval.
Table 1Meta-Analyses of RCTs of Effects of Calcium Supplements on Cardiovascular Events
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Study |
Intervention |
No. |
Endpoint (s) |
Findings |
Comments |
Wang et al. (2010) [46] |
Calcium |
3,861 |
CVD |
RR, 1.14 (0.92–1.41) |
Trial level analysis of 3 published studies |
Bolland et al. (2010) [41] |
Calcium |
11,921 |
MI |
RR, 1.27 (1.01–1.59) |
11 Studies, including previously unpublished data; 23% of MIs were self-reported: exclusion of these raises RR to 1.44 (1.08–1.91) [47] |
Stroke |
RR, 1.12 (0.92–1.36) |
Bolland et al. (2011) [43] |
Calcium±D |
28,072 |
MI |
RR, 1.24 (1.07–1.45) |
WHI data is from women who were not already taking calcium supplements at randomization; 9% of MIs self-reported: exclusion of these raises RR to 1.29 (1.10–1.52) |
Stroke |
RR, 1.15 (1.00–1.32) |
Wang et al. (2012) [50] |
Calcium |
3,861 |
CV events |
RR, 1.14 (0.92–1.41) |
Trial level analysis of 3 published studies |
Calcium+D |
37,653 |
RR, 0.99 (0.79–1.22) |
Included WHI women already taking calcium. WHI dominates outcome |
Mao et al. (2013) [48] |
Calcium |
~7,454 |
MI |
OR, 1.28 (0.97–1.28) |
- |
Stroke |
OR, 1.14 (0.90–1.46) |
Calcium±D |
~39,609 |
MI |
OR, 1.06 (0.92–1.21) |
Included WHI women already taking calcium. WHI dominates outcome |
Lewis et al. (2015) [45] |
Calcium |
6,333 |
MI |
RR, 1.37 (0.98–1.32) |
Excluded men and self-reported events |
Calcium±D |
48,460 |
CHD |
RR, 1.02 (0.96–1.09) |
Included 4 RCTs and the non-RCT of Larsen. WHI women already taking calcium included; 82% weight from WHI [49]. |