Please note:
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.
High blood pressure
The results from intervention studies using magnesium supplements to treat abnormally high blood pressure (‘hypertension’) have been conflicting (4).
While in uncontrolled trials, hypertensive patients on thiazide diuretics experienced decreases in blood pressure when given magnesium supplements, most randomized controlled trials have not been supportive of a blood pressure-lowering effect for magnesium supplementation (3).
Two reviews concluded that well-controlled, long-term clinical trials are needed to determine whether oral magnesium has any therapeutic benefit in hypertensive individuals (12, 13).
Intravenous magnesium is sometimes used by doctors to lower high blood pressure in a ‘hypertensive crisis’.
Preeclampsia
For many years, high-dose intravenous magnesium sulfate has been the treatment of choice for preventing seizures (convulsions) that may occur in association with preeclampsia and eclampsia late in pregnancy (14, 15). Magnesium is believed to relieve blood vessel contraction (‘spasm’) in the brain (‘cerebral’), increasing blood flow to the brain (16, 17).
Cardiovascular Disease
Heart attack
Results of a meta-analysis of randomized controlled trials indicated that an intravenous (IV) magnesium infusion given early after suspected heart attack (‘myocardial infarction’, MI) could decrease the risk of death. The most influential study included in the meta-analysis was a placebo-controlled trial in 2,316 patients that found a significant reduction in mortality in the group of patients given intravenous magnesium sulfate within 24 hours of suspected myocardial infarction (7.8% vs. 10.3% in the placebo group) (18). Follow-up from one to five years after treatment revealed that the mortality from cardiovascular disease was 21% lower in the magnesium-treated group (19).
However, a larger placebo-controlled trial that included more than 58,000 patients found no significant reduction in 5-week mortality in patients treated with intravenous magnesium sulfate within 24 hours of suspected myocardial infarction (20). A U.S. survey of the treatment among more than 173,000 patients with acute MI found that only 5% were given intravenous magnesium in the first 24 hours after MI, and that mortality was higher in patients treated with intravenous magnesium compared to those not treated with magnesium (21).
More recently, a review of 26 clinical trials, including 73,363 patients, concluded that intravenous magnesium likely does not reduce mortality following myocardial infarction and thus should not be used as a treatment (22).
Thus, the use of intravenous magnesium sulfate in the therapy of acute myocardial infarction remains controversial.
Endothelial dysfunction
Research indicates that treatment with magnesium may improve vascular endothelial function in individuals with cardiovascular disease.
A randomized controlled trial in 50 men and women with stable heart (‘coronary’) artery disease found that six months of oral magnesium supplementation (730 mg/day) resulted in a 12% improvement in blood flow-mediated vasodilation compared to placebo (23). Magnesium supplementation also resulted in increased exercise tolerance during an exercise stress test compared to placebo. In another study of 42 patients with coronary artery disease who were already taking low-dose aspirin (an inhibitor of blood clotting), three months of oral magnesium supplementation (800─1,200 mg/day) resulted in an average 35% reduction in formation of a blood clot (‘thrombosis’) (24).
Additionally, a study in 657 women participating in the Nurses' Health Study reported that increasing dietary magnesium intake was associated with decreased blood concentrations of a marker of endothelial dysfunction (25).
In vitro studies have associated low magnesium concentrations with inhibition of endothelial cell division (‘proliferation’) (26). Although preliminary, these studies suggest that magnesium may be beneficial in improving endothelial function in individuals with cardiovascular diseases.
Diabetes mellitus
Magnesium depletion is commonly associated with diabetes mellitus type 1 and type 2: between 25% and 38% of diabetics have been found to have decreased serum levels of magnesium (‘hypomagnesemia’) (27). One cause of the depletion may be increased urinary loss of magnesium, which results from increased urinary excretion of glucose that accompanies poorly controlled diabetes. Magnesium depletion has been shown to worsen the already diminished responsiveness to insulin (‘glucose resistance’) in diabetes, and may adversely affect blood glucose control in diabetics.
One study reported that dietary magnesium supplements (400 mg/day) improved glucose tolerance in elderly individuals (28). More recently, a randomized controlled study in 63 individuals with type 2 diabetes and hypomagnesemia found that those taking an oral magnesium chloride solution (2.5 g/day) for 16 weeks had improved measures of insulin sensitivity and glucose control compared to those taking a placebo (29).
A meta-analysis of nine randomized controlled trials concluded that oral supplemental magnesium may lower fasting blood plasma glucose levels in diabetic individuals (30).
Due to conflicting reports, it is presently unclear whether magnesium supplementation has any therapeutic benefit in type 2 diabetic patients. However, correcting existing magnesium deficiencies may improve glucose metabolism and insulin sensitivity in diabetic individuals.
Large-scale, well-controlled studies are needed to determine whether supplemental magnesium is useful in diabetes.
Osteoporosis
Magnesium comprises about 1% of bone mineral and is known to influence both bone (collagen) matrix and bone mineral metabolism. As the magnesium content of bone mineral decreases, bone crystals become larger and more brittle.
Some studies have found lower magnesium content and larger bone crystals in bones of osteoporotic women compared to non-osteoporotic controls (31). Inadequate blood serum magnesium levels are known to result in low serum calcium levels and resistance to some of the effects of vitamin D, all of which can lead to increased bone loss.
A study in over 900 elderly men and women found higher dietary magnesium intakes were associated with increased bone mineral density (BMD) at the hip in both men and women. However, because magnesium and potassium are present in many of the same foods, the effect of dietary magnesium could not be isolated (32).
Few studies have addressed the effect of magnesium supplementation on bone mineral density or osteoporosis in humans. In a small group of postmenopausal women with osteoporosis, magnesium supplementation of 750 mg/day for the first six months followed by 250 mg/day months for further 18 more months resulted in increased BMD at the wrist after one year, with no further increase after two years of supplementation (33).
A study in postmenopausal women who were taking estrogen replacement therapy and also a multivitamin found that supplementation with an additional 500 mg/day magnesium and 600 mg/day calcium resulted in increased BMD at the heel compared to postmenopausal women receiving only estrogen replacement therapy (34).
Presently, the potential for increased magnesium intake to influence calcium and bone metabolism warrants more research with particular attention to its role in the prevention and treatment of osteoporosis.
Migraine headaches
Individuals who suffer from recurrent migraine headaches have lower intracellular magnesium levels than individuals who do not experience migraines (35). Oral magnesium supplementation has been shown to increase intracellular magnesium levels in individuals with migraines, leading to the hypothesis that magnesium supplementation might be helpful in decreasing the frequency and severity of migraine headaches.
Two randomized controlled trials have demonstrated modest decreases in the frequency of migraine headaches after supplementation with 600 mg/day magnesium (35, 36).
However, another placebo-controlled study found that 485 mg/day magnesium did not reduce the frequency of migraine headaches (37).
More recently, a placebo-controlled trial in 86 children with frequent migraine headaches found that oral magnesium (9 mg/kg body weight/day) reduced headache frequency over the 16-week intervention (38). Although no serious adverse effects were noted during these migraine headache trials, the investigators did note adverse effects such as diarrhea and gastric (stomach) irritation in about 19% to 40% of the individuals taking the magnesium supplements.
Asthma
Blood serum or red blood cell levels of magnesium have not been found to be lower in asthmatic patients compared to non-asthmatic individuals, even during acute asthmatic attacks. Several clinical trials have examined the effect of intravenous magnesium infusions on acute asthmatic attacks.
One randomized controlled trial in 38 adults who did not respond to initial treatment in the emergency room found improved lung function and decreased likelihood of hospitalization when intravenous magnesium sulfate was infused compared to a placebo (39).
However, another controlled study in 48 adults reported that intravenous infusion of magnesium did not improve lung function in patients experiencing an acute asthma attack (40).
A review of seven randomized controlled trials (five adult and two pediatric) concluded that intravenous magnesium sulfate is beneficial in patients with severe, acute asthma (41). In addition, a meta-analysis of five randomized placebo-controlled trials involving 182 children with severe asthma found that intravenous infusion of magnesium was associated with a 71% reduction in the need for hospitalization (42).
At present, available evidence indicates that intravenous magnesium infusion is an efficacious treatment for severe, acute asthma; however, oral magnesium supplementation is of no known value in the management of chronic asthma (43, 44, 45).
Nebulized, inhaled magnesium for treating asthma requires further investigation, although a review of six randomized controlled trials in 296 patients concluded that inhaled magnesium, along with a beta-2-agonist, may improve pulmonary function in patients with acute asthma (46).
Attention deficit/hyperactivity disorder (ADHD)
Some experts believe that children with attention deficit/hyperactivity disorder (ADHD) may be exhibiting the effects of mild magnesium deficiency, such as irritability, decreased attention span, and mental confusion.
In one clinical study in 116 children with ADHD, 95% were magnesium deficient (47).
In a separate clinical study, 75 magnesium-deficient children with ADHD were randomly assigned to receive magnesium supplements in addition to standard treatment or standard treatment alone for 6 months (48). Those who received magnesium demonstrated a significant improvement in behavior, whereas those who received only standard therapy without magnesium exhibited worsening behavior.
These results suggest that magnesium supplementation, or at least high amounts of magnesium in the diet, may prove to be beneficial for children with ADHD.
Infertility and miscarriage
A small clinical study of infertile women as well as women with a history of miscarriage found that low levels of magnesium may impair reproductive function and increase the risk for miscarriage. The authors of the study suggest that one aspect of infertility treatment ─ particularly in women with a history of miscarriage ─ should include magnesium and selenium (49).
More research in this area is needed to evaluate the significance of magnesium.
Premenstrual syndrome (PMS)
Scientific evidence and clinical experience suggest that magnesium supplements may help relieve symptoms associated with PMS, particularly bloating, insomnia, leg swelling, weight gain, and breast tenderness (50).
Preliminary information suggests that magnesium may also be helpful for alleviating mood swings (51).