Summary of findings 1. Calcium supplementation/fortification compared to control for prevention of primary hypertension.
| Calcium supplementation/fortification compared to control for prevention of primary hypertension | |||||
| Patient or population: People who may be at risk for primary hypertension Settings: US (8), New Zealand (3), and one each in The Netherlands, Belgium and Denmark, Guatemala and Iran Intervention: Calcium supplementation/fortification Comparison: Placebo | |||||
| Outcomes | Illustrative blood pressure in control group b | Mean difference in mmHg (95% CIa) | No of participants (studies) | Quality of the evidence (GRADE)c | Comments |
| Systolic blood pressure (range of follow‐up from 4 weeks to 4 years) | 115.62 | 1.37 lower (2.08 lower to 0.66 lower) | 3140 (18 studies) | ⊕⊕⊕⊕ high | Women: ‐1.25 mmHg [95% CI: ‐2.53, 0.03; 8 studies] Men: ‐2.07 mmHg [95% CI: ‐3.56, ‐0.59; 5 studies] Both: ‐1.11 mmHg [95% CI: ‐2.15, ‐0.08; 6 studies] |
| Diastolic blood pressure (range of follow‐up from 4 weeks to 4 years) | 78.17 |
1.45 lower (2.23 lower to 0.67 lower) |
3039 (17 studies) | ⊕⊕⊕⊕ high | Women: ‐1.03 mmHg [95% CI: ‐1.80, ‐0.26; 8 studies] Men: ‐1.91 mmHg [95% CI: ‐2.80, ‐1.02; 5 studies] Both: ‐0.25 mmHg [95% CI: ‐1.08, 0.57; 5 studies] |
| Systolic blood pressure. Dose less than 1000 mg a day (range of follow‐up from 12 weeks to 2 years) | 103.74 | 0.02 lower (2.23 lower to 2.20 higher) | 302 (3 studies) | ⊕⊕⊕⊝ moderate1 | Subgroup analysis by dose |
| Systolic blood pressure. Dose between 1000 mg a day and less than 1500 mg a day (range of follow‐up from 4 weeks to 2 years) | 116.29 | 1.05 lower (1.91 lower to 0.19 lower) | 2488 (9 studies) | ⊕⊕⊕⊕ high | Subgroup analysis by dose |
| Systolic blood pressure. Dose 1500 mg a day or more (range of follow‐up from 4 weeks to 4 years) | 112.85 | 2.79 lower (4.71 lower to 0.86 lower) | 350 (7 studies) | ⊕⊕⊕⊝ moderate1 | Subgroup analysis by dose |
| Systolic blood pressure. Less than 35 years of age (range of follow‐up from 4 weeks to 22 weeks) | 113.23 | 1.79 lower (3.20 lower to 0.38 lower) | 452 (9 studies) | ⊕⊕⊕⊝ moderate1 | Subgroup analysis by age |
| Systolic blood pressure. 35 years or older (range of follow‐up from 4 weeks to 4 years) | 124.20 | 0.97 lower (1.83 lower to 0.10 lower) | 2688 (10 studies) | ⊕⊕⊕⊕ high | Subgroup analysis by age |
| Adverse events (secondary outcome) | One study evaluated side effects, but none were reported. A further two studies mentioned that the supplements were well tolerated. No trials reported any incidence of kidney stone formation, iron deficiency anaemia, anaemia, cardiovascular events, myocardial infarction, stroke or mortality. | ||||
| aCI: Confidence interval; bEstimated using Comprehensive Meta‐Analysis Software Software; cGRADE Working Group grades of evidence | |||||
| High quality: Further research is very unlikely to change our confidence in the estimate of effect. Moderate quality: Further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate. Low quality: Further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate. Very low quality: We are very uncertain about the estimate. |
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1. Downgraded one level for imprecision due to small number of participants.