Comprehensive analytical review of 44 human studies in 43 publications of oral Magnesium (Mg) therapy for hypertension (HT) shows Mg supplements may enhance the blood-pressure (BP) lowering effect of anti-hypertensive medications (medications) in Stage 1 HT subjects. 9 studies conducted on subjects treated with medications continuously >/= 6 months (with </= 2-wk washout) resulted in significant decreases in both SBP and DBP with oral Mg supplements as low as 230 mg (10 mmol) per day. Twice this oral Mg dose, i.e. 460 mg/day, was required to significantly lower both SBP and DBP in 18 of 22 studies conducted on Stage 1 HT subjects either treatment-naïve or with their medication use interrupted >/= 4 weeks within 6 months pre-study. Of the 4 remaining studies showing no BP change at these high Mg doses, two had large placebo effect, a third one had significant baseline discrepancies between Mg-test and placebo groups, and the fourth showed a significant decrease in DBP but not SBP. Thirteen studies on normotensive subjects, both treated and untreated with medications, showed no significant BP lowering effect with oral Mg therapy up to 25 mmol/day (607 mg).
Conclusions: Mg supplements above RDA may be necessary to significantly lower high blood pressure in Stage I HT unless subjects have been continuously treated with anti-HT medications >/= 6 months. Such medication use may lower by half the oral Mg dose needed to significantly decrease high blood pressure. Oral Mg therapy may have no effect in studies with normotensive subjects. Study of oral Mg therapy for severe or complicated hypertension has been neglected. Often the first cardiovascular risk factor to present, high blood pressure may be an early opportunity to correct poor Mg status and its possible complications including cardiovascular disease, respiratory diseases, and type 2 diabetes. Such preventive potential encourages quantification of these findings and testing of these hypotheses with a meta-analysis using categories elucidated by this preliminary study and finally would warrant a call for a prospective study.