Table 3.
Calcium intake in form of diets or supplements and risk for gestational hypertension or effect on blood pressure: a summary of meta-analyses of randomized controlled trials or observational studies.
| Author/Year | No. of Trials | Study Characteristic | No. of Participants | Study Aims | Duration of Trials | Calcium Dosage (Diet or Supplement) | Blood Pressure Lowering in mmHg or RR/OR for Gestational Hypertension (95% CI) | Further Remarks/Summary |
|---|---|---|---|---|---|---|---|---|
| Imdad et al., 2011 [8] | 6 | Randomized controlled trials | Calcium-group: 4919 Control group: 4942 |
Effect of calcium supplementation on gestational hypertensive disorders in studies from developing countries | Calcium supplements in all the included studies were before 20–32 weeks of gestation and continued till delivery. | 0.5–2 g/day | RR: 0.55 (0.36 to 0.85) | Calcium supplementation during pregnancy was associated with a significant reduced risk of acquiring gestational hypertension. |
| Hofmeyr et al., 2014 [43] | 12 trials | Randomized controlled trials | 15,470 women | Assessing the effects of calcium supplementation during pregnancy on hypertensive disorders of pregnancy and related maternal and child outcomes | Calcium supplementation started at the latest from 34 weeks of pregnancy. | High-dose calcium supplementation (≥1 g/day) | RR: 0.65 (0.53 to 0.81) | Average risk of high blood pressure was reduced with calcium supplementation compared with placebo. There was also a reduction in hypertension with low-dose calcium supplementation (<1 g/day). |
| An et al., 2015 [44] | 4 | Randomized controlled trials | Gestational hypertension: 7252 Control group: 7272 Severe gestational hypertension: 6673 Control group: 6684 |
Assessing the effectiveness of calcium supplementation during pregnancy on reducing the risk of hypertensive disorders of pregnancy and related problems. | From ~11–24 weeks of pregnancy to delivery | Supplementation with calcium (at least >1 g/day) | Gestational hypertension: RR: 0.91 (0.84 to 0.99) Severe gestational hypertension: RR: 0.81 (0.60 to 1.09) |
Calcium supplementation appears to reduce the risk of hypertension in pregnancy. No significant reduction in the risk of severe gestational hypertension. |
| Wu and Sun 2017 [46] | 8 | Randomized controlled trials | 36,806 | Evaluation the effect of calcium plus vitamin-D (CaD) supplements on the changes in BP from baseline to the longest follow-up time point in male and female participants. | 8 weeks to 7 years | Intervention dose of calcium (≤1000 mg/day, 5 trials or >1000 mg/day, 3 trials) | Mean differences in SBP: 0.6 (−1 to 2.20) Mean differences in DBP: −0.2 (−0.9 to 0.5) |
Calcium plus vitamin D supplementation slightly increased SBP, but the difference was not statistically significant. Calcium plus vitamin D supplementation did not significantly affected DBP reduction. |
| Cormick et al., 2015 [47] | 16 | Randomized controlled trials | SBP: 3048 (16 studies) DBP: 2947 (15 studies) |
Assessing the efficacy and safety of calcium supplementation versus placebo or control for reducing blood pressure in normotensive people | Median follow up intervention period of 3.5 months | For most studies the intervention was 1000 mg to 2000 mg of elemental calcium per day | Mean difference: SBP: −1.4 (−2.2 to −0.7) DBP: −1 (−1.5 to −0.5) |
The quality of evidence was high for doses of calcium of 1000 to 1500 mg/day and was moderate for lower or higher doses. Calcium intake slightly reduced both SBP and DBP in normotensive people. |
| Observational studies | ||||||||
| Schoenaker et al., 2014 [45] | 16 | Observational studies | Case-control studies: 757 pregnant women Cohort studies: 41,214 pregnant women, 908 gestational hypertension |
Assessing the effect of dietary factors on hypertensive disorders during pregnancy (gestational hypertension and pre-eclampsia) | Highest group >1600 mg/day versus lowest group <1000 mg/day | Gestational hypertension (comparing highest to lowest): OR: 0.63 (0.41 to 0.97) |
Results from case–control studies consistently showed lower reported calcium intake for pregnant women with hypertensive disorders (gestational hypertension and preeclampsia) | |
SBP = Systolic blood pressure; DBP = Diastolic blood pressure.