Minerals // Magnesium
Any dietary or drug treatment with high doses of micronutrients may override the body's own control mechanisms. Therefore, micronutrient therapies may be associated with potential side effects and toxicities. High-dose micronutrients should not be used without medical supervision.
Giving a patient an intravenous (IV) magnesium drip soon after a suspected heart attack (‘myocardial infarction’, MI) could decrease mortality, according to the results of a meta-analysis of randomized controlled trials. The most useful study in the meta-analysis was a placebo- controlled trial conducted on 2,316 participants that found a considerable reduction in the risk of death in the group of patients given intravenous magnesium sulfate less than 24 hours after a suspected heart attack (7.8% vs. 10.3% in the placebo group) (18). Mortality from cardiovascular disease was 21% lower in the magnesium-treated group, as shown by follow-up one to five years after treatment(19).
Fang et al. 2016 described in their meta-analysis of prospective cohort studies that increasing dietary magnesium intake is associated with a reduced risk of stroke, heart failure, diabetes, and all-cause mortality, but not coronary heart disease or total cardiovascular disease (65).
No real reduction in death five weeks after treatment with intravenous magnesium sulfate less than 24 hours after a suspected heart attack was found by a larger placebo- controlled trial that examined over 58,000 patients (20). In an American study covering over 173,000 heart attack patients showed that only 5% were given intravenous magnesium within 24 hours of their heart attack. It also showed that mortality was higher among those who had received magnesium than those who had not (21).
A more recent overview of 26 clinical trials covering 73,363 patients came to the conclusion that intravenous magnesium is unlikely to reduce mortality after a heart attack and so is inadvisable as a treatment (22).
As a result, intravenous magnesium sulfate in the treatment of heart attacks is still controversial.
Six months of therapy with magnesium supplementation (730 mg/day) was found to result in a 12% improvement in blood flow-mediated vasodilation compared to a placebo in a randomized controlled trial that followed 50 participants with stable heart (‘coronary’) artery disease (23). Increased tolerance to exercise during a stress test compared to a placebo was also found to result from magnesium supplementation. A different study showed that three months of magnesium supplementation (800─1,200 mg/day) produced an average 35% reduction in blood clot formation (‘thrombosis’). This particular study followed 42 participants with coronary artery disease who were already on low doses of aspirin (a blood clot inhibitor) (24).
Inhibition of endothelial cell division (‘proliferation’) has been linked to low magnesium intake in in vitro studies(26). There is a suggestion that magnesium may be useful in improving endothelial function in people with cardiovascular diseases, even though these studies are in their early stages.
Also in regard to arrhythmia the scientific evidence is controversially discussed. Two meta-analysis of randomized clinical trials support that magnesium infusion reduces the incidence of postoperative atrial fibrillation after coronary artery bypass grafting (66) and the risk of supraventricular arrhythmias after cardiac surgery by 23% (atrial fibrillation by 29%) and of ventricular arrhythmias by 48% (67). Therefore, the European Association for Cardiothoracic Surgery and the Canadian Cardiovascular Society recommend prophylaxis with intravenous MgSO4 (69).
Beside the positive effects of intravenous magnesium it is, however, not useful in monomorphic ventricular tachycardia and shock-resistant ventricular fibrillation (68).
People with high blood pressure taking thiazide diuretics showed decreases in blood pressure with magnesium supplementation in uncontrolled trials, yet results from most randomized controlled trials demonstrated no blood pressure-lowering for this (3).
To ascertain whether magnesium supplementation has any effect as a treatment for people with high blood pressure, two studies have come to the conclusion that controlled, long-term trials are required (12, 13).
Doctors occasionally use a magnesium drip to lower blood pressure in a ‘hypertensive crisis’.
A meta-analysis from 2017 shows that magnesium intake, in a dose-dependent manner, is associated with a reduced risk of hypertension (70).
High doses of magnesium have been the preferred treatment for many years for seizure (convulsions) prevention late in pregnancy. These are often the result of preeclampsia and eclampsia (14, 15). This treatment is thought to increase blood flow to the brain by alleviating cerebral blood vessel spasm (16, 17).
About 1% of bone mineral is magnesium. It has an effect on the bone (collagen) matrix and bone mineral metabolism. Bone crystals get bigger and become more brittle as the magnesium in bone mineral decreases.
Compared to non- osteoporotic controls, a few studies have shown that osteoporotic women have lower magnesium levels and bigger bone crystals (31). A higher rate of bone loss can be caused by insufficient magnesium in the blood, which has been demonstrated to result in low blood calcium levels, and also counteracts some effects of vitamin D.
Increased bone mineral density (BMD) in the pelvis in both men and women was linked to increased magnesium consumption, according to a study following over 900 elderly participants. The effect of magnesium could not however be seen on its own because magnesium and potassium can be found in many of the same foodstuffs (32).
The effect of magnesium therapy on bone mineral density or osteoporosis has been assessed by very few studies. The result of supplementation with 750 mg of magnesium per day for the first six months followed by 250 mg/day for an additional 18 months was an increased BMD in the wrist after a year in a small group of postmenopausal women with osteoporosis. No further increase was observed after a second year of treatment (33).
A study in postmenopausal women on HRT as well as a multivitamin tablet found that an extra 500 mg of magnesium a day and 600 mg of calcium a day produced an increased BMD in the heel compared to postmenopausal women only receiving HRT (34).
A meta-analysis and systematic review of dietary magnesium intake and BMD and risk of fracture found a positive marginal significant correlation between magnesium intake and BMD in femoral neck and total hip, but none in lumbar spine (71).
Magnesium’s potential capacity to positively affect calcium and bone metabolism with increased consumption deserves further research. Special attention should be paid to its role in osteoporosis prevention and treatment.
Between 25% and 38% of sufferers of diabetes mellitus type 1 and type 2 have been shown to have reduced blood levels of magnesium (‘hypomagnesemia’) (27). Increased urinary loss of magnesium could be a cause of the depletion. This is due to the fact that more glucose is excreted in the urine. Loss of magnesium further inhibits the patient’s responsiveness to insulin (‘glucose resistance’). It could also have a negative effect on blood glucose control among diabetics.
Dietary supplementation with magnesium (400 mg/day) was shown to improve glucose tolerance in elderly participants in one study (28). A more recent randomized controlled study following 63 men and women with type 2 diabetes and hypomagnesemia demonstrated that participants on an oral magnesium chloride solution (2.5 g/day) for 16 weeks showed improved insulin sensitivity and glucose control compared to the placebo group (29).
At the moment it has still not been established whether magnesium supplementation is at all beneficial for type 2 diabetic patients because of the conflicting nature of the available results. Rectifying existing magnesium deficiencies in diabetics could lead to an improvement in glucose metabolism and insulin sensitivity.
To determine whether or not supplemental magnesium is beneficial for diabetics, more large-scale, well-controlled studies are needed.
Even during severe asthmatic attacks, research has not shown blood serum or red blood cell levels of magnesium to be lower in asthmatic individuals compared to individuals without asthma. The effect of intravenous magnesium drips on severe asthmatic attacks has been investigated in a few clinical trials.
Improved lung function and decreased incidence of hospitalization was demonstrated with an intravenous magnesium drip compared to a placebo. This was found in a randomized controlled trial following 38 participants who did not respond to initial treatment in the emergency room (39).
Conversely, magnesium was not found to have a beneficial effect on lung function during a different controlled study following 48 patients experiencing a severe asthma attack (40).
Yet intravenous magnesium sulfate was found to be beneficial for patients with severe, acute asthma according to a review of seven randomized controlled trials (five following adults and two following children) (41). Furthermore, an intravenous infusion of magnesium was linked to a 71% decrease in hospitalization, according to a meta-analysis of five randomized placebo- controlled trials following 182 children with severe asthma (42).
Further tests are needed to ascertain potential benefits for asthma sufferers of nebulized magnesium in inhalers. A review of six randomized controlled trials following 296 participants showed promising results. The review focused on magnesium inhaled along with a beta-2-agonist (46).
People who do not experience migraines have higher intracellular magnesium levels than people who do (35). Magnesium supplementation may theoretically help to decrease the frequency and painfulness of migraine headaches since it has been demonstrated to increase intracellular magnesium levels in people who suffer from them.
However, no effect was observed in another placebo- controlled study supplementing 485 mg magnesium per day (37,72).
A more recent placebo- controlled trial following 86 children suffering from frequent migraines demonstrated that oral magnesium supplementation (9 mg/kg body weight/day) reduced migraine frequency over a 16-week period (38). The investigators did however observe negative side-effects like diarrhea and stomach irritation in around 19% to 40% of the participants.
Infertility and miscarriage
Insufficient magnesium intake may disrupt reproductive function and increase the incidence miscarriage according to a small-scale clinical study of infertile women and women who had miscarried in the past. The study suggests that magnesium and selenium should be included in infertility treatment, particularly for women who have miscarried in the past (49).
The importance of magnesium needs to be the subject of further study.
Premenstrual syndrome (PMS)
Symptoms associated with PMS such as bloating, insomnia, leg swelling, weight gain, and breast tenderness could be positively affected by magnesium supplementation (50).
There is also an indication that magnesium supplementation could also prove effective in alleviating mood swings (51).
Attention deficit/hyperactivity disorder (ADHD)
Mild magnesium deficiency could be behind attention deficit/hyperactivity disorder (ADHD) according to some scientists. Symptoms such as irritability, decreased attention span, and mental confusion are consistent with both.
95% of children with ADHD were discovered to exhibit a magnesium deficiency in one clinical study following 116 children (47).
Another clinical study showed that children who received magnesium in addition to ADHD treatment exhibited a considerable behavioral improvement, whereas those who received only standard treatment without magnesium showed worsening behavior. In this study, 75 magnesium-deficient children with ADHD were randomly assigned to receive magnesium supplementation in addition to standard therapy or standard therapy alone over a period of 6 months (48). Newest reviews report that magnesium may reduce ADHD symptoms in children, but more evidence is needed (73,74).
Children with ADHD may therefore benefit from magnesium supplementation, or at least increased amounts of dietary magnesium.
Authored by Dr Peter Engel in 2010 and reviewed and revised by Angelika Friedel on 22.05.2017.