Magnesium deficiency frequently occurs in people with CHF, and such a deficiency may lead to heart arrhythmias. Magnesium supplements have reduced the risk of these arrhythmias.⁷ People with CHF are often given drugs that deplete both magnesium and potassium; a deficiency of either of these minerals may lead to an arrhythmia.⁸ Many doctors suggest magnesium supplements of 300 mg per day.

Magnesium deficiency has been proposed as one cause of the symptoms that occur in association with MVP.⁹ In a study of people with severe MVP symptoms, blood levels of magnesium were low in 60% of cases. Those people with low magnesium levels participated in a double-blind trial, in which they received a placebo or magnesium (500 mg per day for one week, then about 335 mg per day for four weeks). People receiving magnesium experienced a significant reduction in symptoms of weakness, chest pain, anxiety, shortness of breath, and palpitations.¹⁰

A double-blind trial investigated the effect of oral magnesium supplementation on arrhythmic episodes in people with congestive heart failure. Those people taking 3.2 grams per day of magnesium chloride (equivalent to 384 mg per day of elemental magnesium) had between 23% and 52% fewer occurrences of specific types of arrhythmia during the six-week study, compared with those taking placebo.¹¹ Lower serum concentrations of magnesium were found to be associated with a higher incidence of arrhythmia in a large population study.¹² The anti-arrhythmic properties of magnesium appear to be specific. For example, magnesium is clearly able to prevent a drug-induced arrhythmia called torsade de pointes,¹³ but it does not appear to prevent atrial fibrillation.¹⁴ A doctor should supervise any use of magnesium for cardiac arrhythmia.

Magnesium plays a role in controlling muscle tone and could be important in preventing menstrual cramps.^15,16 Magnesium supplements have been reported in preliminary and double-blind European research to reduce symptoms of dysmenorrhea.^17,18,19 In one of these double-blind trials, women took 360 mg per day of magnesium for three days beginning on the day before menses began.¹⁸

Numerous studies have shown that poor magnesium status is associated with insulin resistance and type 2 diabetes.^20,21,22,23 Furthermore, diabetes itself causes increased magnesium loss, resulting in a vicious cycle of dropping magnesium levels and worsening insulin resistance.^24,25 Low magnesium levels have also been correlated with poor blood glucose control and increased risk of complications such as heart disease, kidney disease, and nerve damage in those with type 2 diabetes.^{26,27,28,29,30} Moreover, meta-analyses of randomized controlled trials have concluded that magnesium supplementation can lower blood pressure and decrease the risk of diabetes-related cardiovascular disease in people with type 2 diabetes.^31,32

Taking 250 mg of elemental magnesium (from magnesium oxide, gluconate, and lactate) per day for three months improved glycemic control and insulin sensitivity in a randomized controlled trial with 42 participants with type 2 diabetes.³³ In a placebo-controlled trial, patients with diabetes-related kidney failure taking 250 mg of elemental magnesium (from magnesium oxide) per day for 24 weeks had improved vascular health, as well as reduced insulin, total cholesterol, LDL-cholesterol, and C-reactive protein levels, Hgb1c values, and insulin resistance scores, and increased antioxidant capacity.³⁴ However, another placebo-controlled trial that included people with type 2 diabetes and related kidney disease found the combination of 250 mg magnesium (from magnesium oxide) plus 47 mg calcium (from calcium carbonate) per day improved lipid profiles but had no effect on glucose control and worsened insulin resistance after 12 weeks.³⁵ Many doctors recommend that people with diabetes supplement with 200 to 600 mg per day of elemental magnesium from a highly bioavailable magnesium salt without added calcium.

Magnesium plays a role in controlling muscle tone and could be important in preventing menstrual cramps.^36,37 Magnesium supplements have been reported in preliminary and double-blind European research to reduce symptoms of dysmenorrhea.^38,39,40 In one of these double-blind trials, women took 360 mg per day of magnesium for three days beginning on the day before menses began.³⁹

Compared with healthy people, people with migraines have been found to have lower blood and brain levels of magnesium.^41,42,43,44 Preliminary research in a group of women (mostly premenopausal) showed that supplementing with magnesium (usually 200 mg per day) reduced the frequency of migraines in 80% of those treated.⁴⁵ In a double-blind trial of 81 people with migraines, 600 mg of magnesium per day was significantly more effective than placebo at reducing the frequency of migraines.⁴⁶ Another double-blind trial found that taking 360 mg of magnesium per day decreased the number of days on which premenstrual migraines occurred.⁴⁷ One double-blind trial found no benefit from 486 mg of magnesium per day for three months. However, that study defined improvement according to extremely strict criteria, and even some known anti-migraine drugs have failed to show benefit when tested using those criteria.⁴⁸ Intravenous magnesium has been reported to produce marked and sometimes complete symptom relief during acute migraines, usually within 15 minutes or less.⁴⁹

Magnesium deficiency has also been implicated as a possible cause of GH.^50,51,52 Dietary intake of magnesium is below recommended levels for many women during pregnancy.^53,50 Magnesium supplementation has been reported to reduce the incidence of GH in preliminary⁵⁰ and many double-blind trials.^56,57,58 In addition to preventing GH, magnesium supplementation has also been reported to reduce the severity of established GH in one study.⁵⁹ Amounts used in studies on GH range from 165 to 365 mg of supplemental magnesium per day.