A Cochrane review 1 [Abstract] included 12 studies with a total of 545 subjects with raised systolic blood pressure (SBP) ≥140 mmHg or diastolic blood pressure (DBP) ≥85 mmHg. Combining all trials, participants receiving magnesium supplements as compared to control did not significantly reduce SBP (MD -1.3 mmHg, 95% CI -4.0 to 1.5, I2 =67%), but reduced statistically significantly DBP (MD -2.2 mmHg, 95% CI -3.4 to -0.9, I2 =47%).
A meta-analysis 2 included 22 studies with a total of 1 173 subjects. Supplemented elemental magnesium range was 120-973 mg (mean dose 410 mg=16.9 mmol), and the duration of treatment with magnesium ranged from 3 to 24 weeks, with a mean duration of 11.3 weeks. Effect size was calculated using Hedges G. Combining all data, an overall effect of 0.36 (95% CI 0.27 to 0.44) for DBP and 0.32 (95% CI 0.23 to 0.41) for SBP was observed. These effect sizes translate to an actual reduction of 2-3 mm Hg for DBP and 3-4 mm Hg for SBP. When a subanalysis for dosage was carried out (<370 mg Mg and ≥370 mg Mg/day), results for both SBP and DBP showed greater efficacy at the higher dose (effect size for DBP 0.66, 95% CI 0.51 to 0.82 and for SBP 0.70, 95% CI 0.56 to 0.89).
Comment: The quality of evidence is downgraded by inconsistency (variability in results).
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