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Magnesium plays important roles in the structure and the function of the human body. The adult human body contains about 25 grams of magnesium. Over 60% of all the magnesium in the body is found in the skeleton, about 27% is found in muscle, 6% to 7% is found in other cells, and less than 1% is found outside of cells (1).
Magnesium is involved in more than 300 essential metabolic reactions, some of which are discussed below (2).
The metabolism of carbohydrates and fats to produce energy requires numerous magnesium-dependent chemical reactions. Magnesium is required by the adenosine triphosphate (ATP)-synthesizing protein in mitochondria. ATP, the molecule that provides energy for almost all metabolic processes, exists primarily as a complex with magnesium (MgATP) (3).
Synthesis of essential molecules
Magnesium is required for a number of steps during synthesis of deoxyribonucleic acid (DNA), ribonucleic acid (RNA), and proteins. Several enzymes participating in the synthesis of carbohydrates and lipids require magnesium for their activity. Glutathione, an important antioxidant, requires magnesium for its synthesis (3).
Ion transport across cell membranes
Magnesium is required for the active transport of ions like potassium and calcium across cell membranes. Through its role in ion transport systems, magnesium affects the conduction of nerve impulses, muscle contraction, and normal heart rhythm (3).
Cell signaling requires MgATP for the phosphorylation of proteins and the formation of the cell-signaling molecule, cyclic adenosine monophosphate (cAMP). cAMP is involved in many processes, including the secretion of parathyroid hormone (PTH) from the parathyroid glands (see Vitamin D and Calcium for additional discussions regarding the role of PTH) (3).
High doses of zinc in supplemental form apparently interfere with the absorption of magnesium. One study reported that zinc supplements of 142 mg/day in healthy adult males significantly decreased magnesium absorption and disrupted magnesium balance (the difference between magnesium intake and magnesium loss) (4).
Large increases in the intake of dietary fiber have been found to decrease magnesium utilization in experimental studies. However, the extent to which dietary fiber affects magnesium nutritional status in individuals with a varied diet outside the laboratory is not clear (2, 3).
Dietary protein may affect magnesium absorption. One study in adolescent boys found that magnesium absorption was lower when protein intake was less than 30 grams/day, and higher protein intakes (93 grams/day vs. 43 grams/day) were associated with improved magnesium absorption in adolescents (5).
Vitamin D and calcium
The active form of vitamin D (calcitriol) may slightly increase intestinal absorption of magnesium (6). However, it is not clear whether magnesium absorption is calcitriol-dependent as is the absorption of calcium and phosphate. High calcium intake has not been found to affect magnesium balance in most studies. Inadequate blood magnesium levels are known to result in low blood calcium levels, resistance to parathyroid hormone (PTH) action, and resistance to some of the effects of vitamin D (2, 3).
Magnesium deficiency in healthy individuals who are consuming a balanced diet is quite rare because magnesium is abundant in both plant and animal foods and because the kidneys are able to limit urinary excretion of magnesium when intake is low. The following conditions increase the risk of magnesium deficiency (1):
Although severe magnesium deficiency is uncommon, it has been induced experimentally. When magnesium deficiency was induced in humans, the earliest sign was decreased serum magnesium levels (hypomagnesemia). Over time, serum calcium levels also began to decrease (hypocalcemia) despite adequate dietary calcium. Hypocalcemia persisted despite increased secretion of parathyroid hormone (PTH), which regulates calcium homeostasis. Usually, increased PTH secretion quickly results in the mobilization of calcium from bone and normalization of blood calcium levels. As the magnesium depletion progressed, PTH secretion diminished to low levels. Along with hypomagnesemia, signs of severe magnesium deficiency included hypocalcemia, low serum potassium levels (hypokalemia), retention of sodium, low circulating levels of PTH, neurological and muscular symptoms (tremor, muscle spasms, tetany), loss of appetite, nausea, vomiting, and personality changes (3).
In 1997, the Food and Nutrition Board of the Institute of Medicine increased the recommended dietary allowance (RDA) for magnesium, based on the results of recent, tightly controlled balance studies that utilized more accurate methods of measuring magnesium (2). Balance studies are useful for determining the amount of a nutrient that will prevent deficiency; however, such studies provide little information regarding the amount of a nutrient required for chronic disease prevention or optimum health.
|Recommended Dietary Allowance (RDA) for Magnesium|
|Life Stage||Age||Males (mg/day)||Females (mg/day)|
|Infants||0-6 months||30 (AI)||30 (AI)|
|Infants||7-12 months||75 (AI)||75 (AI)|
|Adults||31 years and older||420||320|
|Pregnancy||18 years and younger||-||400|
|Pregnancy||31 years and older||-||360|
|Breast-feeding||18 years and younger||-||360|
|Breast-feeding||31 years and older||-||320|
Low magnesium intakes have been associated with the diagnosis of metabolic syndrome. The concomitant presentation of several metabolic disorders in an individual, including dyslipidemia, hypertension, insulin resistance, and obesity, increases the risk for type 2 diabetes mellitus and cardiovascular disease. Systemic inflammation, which contributes to the development of metabolic disorders, has been inversely correlated with magnesium intakes in a cross-sectional study of 11,686 middle-aged women; the lowest prevalence of metabolic syndrome was found in the group of women with the highest quintile of magnesium intakes (median intake, 422 mg/day) (9).
Large epidemiological study studies suggest a relationship between magnesium and blood pressure. However, the fact that foods high in magnesium (fruit, vegetables, whole grains) are frequently high in potassium and dietary fiber has made it difficult to evaluate the independent effects of magnesium on blood pressure. A prospective cohort study of more than 30,000 male health professionals found an inverse association between dietary fiber, potassium, and magnesium and the development of hypertension over a four-year period (10). In a similar study of more than 40,000 female registered nurses, dietary fiber and dietary magnesium were each inversely associated with systolic and diastolic blood pressures in those who did not develop hypertension over the four-year study period, but neither dietary fiber nor magnesium was related to the risk of developing hypertension (11). The Atherosclerosis Risk in Communities (ARIC) study examined dietary magnesium intake, magnesium blood levels, and risk of developing hypertension in 7,731 men and women over a six-year period (12). The risk of developing hypertension in both men and women decreased as serum magnesium levels increased, but the trend was statistically significant only in women.
However, circulating magnesium represents only 1% of total body stores and is tightly regulated; thus, serum magnesium levels might not best reflect magnesium status. A recent prospective study that followed 5,511 men and women for a median period of 7.6 years found that the highest levels of urinary magnesium excretion corresponded to a 25% reduction in risk of hypertension, but plasma magnesium levels were not correlated with risk of hypertension (13). In cohort of 28,349 women followed for 9.3 years, the risk of hypertension was 7% lower for those with the highest magnesium intakes (434 mg/day vs. 256 mg/day) (14). The relationship between magnesium intake and risk of hypertension suggests that magnesium supplementation might play a role in preventing hypertension; however, randomized controlled trials are needed to assess whether supplemental magnesium might help prevent hypertension in high-risk individuals.
Public health concerns regarding the epidemics of obesity and type 2 diabetes mellitus and the prominent role of magnesium in glucose metabolism have led scientists to investigate the relationship between magnesium intake and type 2 diabetes mellitus. A prospective study that followed more than 25,000 individuals, 35 to 65 years of age, for seven years found no difference in incidence of diabetes mellitus when comparing the highest (377 mg/day) quintile of magnesium intake to the lowest (268 mg/day) (15). However, inclusion of this study in a meta-analysis of eight cohort studies showed that risk of type 2 diabetes was inversely correlated with magnesium intake (15). A second meta-analysis found that an increase of 100 mg/day in magnesium intake was associated with a 15% decrease in the risk of developing type 2 diabetes (16). The most recent meta-analysis of 13 observational studies, published in the last 15 years and including almost 540,000 individuals and 24,500 new cases of diabetes, found higher magnesium intakes were associated with a lower risk of diabetes (17).
Insulin resistance, which is characterized by alterations in both insulin secretion by the pancreas and insulin action on target tissues, has been linked to magnesium deficiency. An inverse association between magnesium intakes and fasting insulin levels was evidenced in a meta-analysis of 11 cohort studies that followed more than 36,000 participants without diabetes (18). It is thought that pancreatic beta cells, which regulate insulin secretion and glucose tolerance, could become less responsive to changes in insulin sensitivity in magnesium-deficient subjects (19). A randomized, double-blind, placebo-controlled trial, which enrolled 97 individuals (without diabetes and with normal blood pressure) with significant hypomagnesemia (serum magnesium level ≤ 0.70 mmoles/L), showed that daily consumption of 638 mg of magnesium (from a solution of magnesium chloride) for three months improved the function of pancreatic beta cells, resulting in lower fasting glucose and insulin levels (20). Increased insulin sensitivity also accompanied the correction of magnesium deficiency in patients diagnosed with insulin resistance but not diabetes (21). Another study found that supplementation with 365 mg/day of magnesium (from magnesium aspartate hydrochloride) for six months reduced insulin resistance in 47 overweight individuals even though they displayed normal values of serum and intracellular magnesium (22). This suggests that magnesium might have additive effects on glucose tolerance and insulin sensitivity that go beyond the normalization of physiologic serum concentrations in deficient individuals.
A number of studies have found decreased mortality from cardiovascular diseases in populations who routinely consume "hard" water. Hard (alkaline) water is generally high in magnesium but may also contain more calcium and fluoride than "soft" water, making the cardioprotective effects of hard water difficult to attribute to magnesium alone (23). One large prospective study (almost 14,000 men and women) found a significant trend for increasing serum magnesium levels to be associated with decreased risk of coronary heart disease (CHD) in women but not in men (24). However, the risk of CHD in the lowest quartile of dietary magnesium intake was not significantly higher than the risk in the highest quartile in men or women. This prospective study was included in a meta-analysis of 14 studies that found a 22% lower risk of CHD (but not fatal CHD) per 200 mg/day incremental intake in dietary magnesium (25). In another prospective study, which followed nearly 90,000 female nurses for 28 years, women in the highest quintile of magnesium intake had a 39% lower risk of fatal myocardial infarction (but not nonfatal myocardial infarction) compared to those in the lowest quintile (>342 mg/day versus <246 mg/day) (26). Higher magnesium intakes were associated with an 8%-11% reduction in stroke risk in two meta-analyses of prospective studies, each including over 240,000 participants (27, 28). Additionally, a meta-analysis of 13 prospective studies in over 475,000 participants reported that the risk of total cardiovascular events, including stroke, nonfatal myocardial infarction, and CHD, was 15% lower in individuals with higher intakes of magnesium (29). Finally, a meta-analysis of six prospective studies found no association between magnesium intake and cardiovascular mortality risk (30). However, a recent prospective study that followed 3,910 subjects for 10 years found significant correlations between hypomagnesemia and all-cause mortality, including cardiovascular-related mortality (31). Presently, well-controlled intervention trials are required to assess the benefit of magnesium supplementation in the prevention of cardiovascular diseases.
Occurrence of hypomagnesemia has been reported in patients who suffered from a subarachnoid hemorrhage caused by the rupture of a cerebral aneurysm (32). Poor neurologic outcomes following an aneurysmal subarachnoid hemorrhage (aSAH) have been linked to inappropriate calcium-dependent contraction of arteries (known as cerebral arterial vasospasm), leading to delayed cerebral ischemia (33). Magnesium sulfate is a calcium antagonist and potent vasodilator that has been considered in the prevention of vasospasm after aSAH. Several randomized controlled trials have assessed the effect of intravenous (IV) magnesium sulfate infusions. A meta-analysis of nine randomized controlled trials found that magnesium therapy after aSAH significantly reduced vasospasm but failed to prevent neurologic deterioration or decrease the risk of death (34). The most recent meta-analysis of 13 trials in 2,413 aSAH patients concluded that the infusion of magnesium sulfate had no benefits in terms of neurologic outcome and mortality, despite a reduction in the incidence of delayed cerebral ischemia (35). At present, the data advise against the use of magnesium supplementation in clinical practice for aSAH patients after normalization of their magnesium status.
Atrial arrhythmia is a condition defined as the occurrence of persistent heart rate abnormalities that often complicate the recovery of patients after cardiac surgery. The use of magnesium in the prophylaxis of postoperative atrial arrhythmia after coronary artery bypass grafting has been evaluated as a sole or adjunctive agent to classical antiarrhythmic molecules (namely, beta-blockers and amiodarone) in several prospective, randomized controlled trials. A meta-analysis of 21 intervention studies showed that intravenous magnesium infusions could significantly reduce postoperative atrial arrhythmia in treated compared to untreated patients (36). However, a meta-analysis of five randomized controlled trials concerned with rhythm-control prophylaxis showed that intravenous magnesium added to beta-blocker treatment did not decrease the risk of atrial arrhythmia compared to beta-blocker alone and was associated with more adverse effects (bradycardia and hypotension) (37). Presently, the findings support the use of beta-blockers and amiodarone, but not magnesium, in patients with contraindications to first-line antiarrhythmics.
Although decreased bone mineral density (BMD) is the primary feature of osteoporosis, other osteoporotic changes in the collagenous matrix and mineral components of bone may result in bones that are brittle and more susceptible to fracture. Magnesium comprises about 1% of bone mineral and is known to influence both bone matrix and bone mineral metabolism. As the magnesium content of bone mineral decreases, apatite crystals of bone become larger and more brittle. Some studies have found lower magnesium content and larger apatite crystals in bones of women with osteoporosis compared to women without the disease (38). Inadequate serum magnesium levels are known to result in low serum calcium levels, resistance to parathyroid hormone (PTH) action, and resistance to some of the effects of vitamin D (calcitriol), all of which can lead to increased bone loss (see Vitamin D and Calcium). A study of over 900 elderly men and women found that higher dietary magnesium intakes were associated with increased 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 (39). A cross-sectional study in over 2,000 elderly individuals reported that magnesium intake was positively associated with total-body BMD in white men and women but not in black men and women (40). More recently, a large cohort study conducted in almost two-thirds of the Norwegian population found the level of magnesium in drinking water was inversely correlated with risk of hip fracture (41).
Few studies have addressed the effect of magnesium supplementation on BMD 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 for 18 more months resulted in increased BMD at the wrist after one year, with no further increase after two years of supplementation (42). A study in postmenopausal women who were taking estrogen replacement therapy and also a multivitamin found that supplementation with an additional 500 mg/day of magnesium and 600 mg/day of calcium resulted in increased BMD at the heel compared to postmenopausal women receiving only estrogen replacement therapy (43). Evidence is not yet sufficient to suggest that supplemental magnesium could be recommended in the prevention of osteoporosis unless normalization of serum magnesium levels is required. Moreover, it appears that high magnesium levels could be harmful to skeletal health by interfering with the action of the calciotropic hormones, PTH and calcitriol (44). 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.
The use of pharmacologic doses of magnesium to treat specific diseases is discussed below. Although many of the cited studies utilized supplemental magnesium at doses considerably higher than the tolerable upper intake level (UL), which is 350 mg/day set by the Food and Nutrition Board (see Safety), it is important to note that these studies were all conducted under medical supervision. Because of the potential risks of high doses of supplemental magnesium, especially in the presence of impaired kidney function, any disease treatment trial using magnesium doses higher than the UL should be conducted under medical supervision.
Preeclampsia and eclampsia
Preeclampsia and eclampsia are pregnancy-specific conditions that may occur anytime after 20 weeks of pregnancy through six weeks following birth. Approximately 7% of pregnant women in the US develop preeclampsia-eclampsia. Preeclampsia (sometimes called toxemia of pregnancy) is defined as the presence of elevated blood pressure (hypertension), protein in the urine, and severe swelling (edema) during pregnancy. Eclampsia occurs with the addition of seizures to the triad of symptoms and is a significant cause of perinatal and maternal death (45). Although cases of preeclampsia are at high risk of developing eclampsia, one-quarter of eclamptic women do not initially exhibit preeclamptic symptoms (46). For many years, high-dose intravenous magnesium sulfate has been the treatment of choice for preventing eclamptic seizures that may occur in association with preeclampsia-eclampsia late in pregnancy or during labor (47, 48). A systematic review of seven randomized trials compared the administration of magnesium sulfate with diazepam (a known anticonvulsant) treatment on perinatal outcomes in 1,396 women with eclampsia. Risks of recurrent seizures and maternal death were significantly reduced by the magnesium regimen compared to diazepam. Moreover, the use of magnesium for the care of eclamptic women resulted in newborns with higher Apgar scores; there was no significant difference in the risk of preterm birth and perinatal mortality (46). Additional research has confirmed that infusion of magnesium sulfate should always be considered in the management of preeclampsia and eclampsia to prevent initial and recurrent seizures (49).
While intravenous magnesium sulfate is included in the medical care of preeclampsia and eclampsia, the American College of Obstetricians and Gynecologists and the Society for Maternal-Fetal Medicine support its use in two additional situations: specific conditions of short-term prolongation of pregnancy and neuroprotection of the fetus in anticipated premature delivery (50). The relationship between magnesium sulfate and risk of cerebral damage in premature infants has been assessed in observational studies. A meta-analysis of six case-control and five prospective cohort studies showed that the use of magnesium significantly reduced the risk of cerebral palsy, as well as mortality (51). However, the high degree of heterogeneity among the cohort studies and the fact that corticosteroid exposure (which is known to decrease antenatal mortality) was higher in the cases of children exposed to magnesium compared to controls imply a cautious interpretation of the results. However, a meta-analysis of five randomized controlled trials, which included a total of 6,145 babies, found that magnesium therapy given to mothers delivering before term decreased the risk of cerebral palsy and gross motor dysfunction, without modifying the risk of other neurologic impairments or mortality in early childhood (52). Another meta-analysis conducted on five randomized controlled trials found that intravenous magnesium administration to newborns who suffered from perinatal asphyxia could be beneficial in terms of short-term neurologic outcomes, although there was no effect on mortality (53). Nevertheless, additional trials are needed to evaluate the long-term benefits of magnesium in pediatric care.
While results from intervention studies have not been entirely consistent (2), the latest review of the data highlighted a therapeutic benefit of magnesium supplements in treating hypertension. A recent meta-analysis examined 22 randomized, placebo-controlled trials of magnesium supplementation conducted in 1,173 individuals with either a normal blood pressure (normotensive) or hypertension, both treated or untreated with medications. Oral supplementation with magnesium (mean dose of 410 mg/day; range of 120 to 973 mg/day) for a median period of 11.3 months significantly reduced systolic blood pressure by 2-3 mm Hg and diastolic blood pressure by 3-4 mm Hg (54); a greater effect was seen at higher doses (≥370 mg/day). The results of 19 of the 22 trials included in the meta-analysis were previously reviewed together with another 25 intervention studies (55). The systematic examination of these 44 trials suggested a blood pressure-lowering effect associated with supplemental magnesium in hypertensive but not in normotensive individuals. Magnesium doses required to achieve a decrease in blood pressure appeared to depend on whether subjects with high blood pressure were treated with antihypertensive medications, including diuretics. Intervention trials on treated subjects showed a reduction in hypertension with magnesium doses from 243 mg/day to 486 mg/day, whereas untreated patients required doses above 486 mg/day to achieve a significant decrease in blood pressure. While oral magnesium supplementation may be helpful in hypertensive individuals who are depleted of magnesium due to chronic diuretic use and/or inadequate dietary intake (56), several dietary factors play a role in hypertension. For example, adherence to the DASH diet—a diet rich in fruit, vegetables, and low-fat dairy and low in saturated and total fats—has been linked to significant reductions in systolic and diastolic blood pressures (57). See the article in the Spring/Summer 2009 Research Newsletter, Dietary and Lifestyle Strategies to Control Blood Pressure.
Results of a meta-analysis of randomized, placebo-controlled trials indicated that an intravenous (IV) magnesium infusion given early after suspected myocardial infarction (MI) could decrease the risk of death. The most influential study included in the meta-analysis was a randomized, placebo-controlled trial in 2,316 patients that found a significant reduction in mortality (7.8% all-cause mortality in the experimental group vs. 10.3% all-cause mortality in the placebo group) in the group of patients given intravenous magnesium sulfate within 24 hours of suspected myocardial infarction (58). Follow-up from one to five years after treatment revealed that the mortality from cardiovascular disease was 21% lower in the magnesium treated group (59). However, a larger placebo-controlled trial that included more than 58,000 patients found no significant reduction in five-week mortality in patients treated with intravenous magnesium sulfate within 24 hours of suspected myocardial infarction, resulting in controversy regarding the efficacy of the treatment (60). A US survey of the treatment of more than 173,000 patients with acute MI found that only 5% were given IV magnesium in the first 24 hours after MI, and that mortality was higher in patients treated with IV magnesium compared to those not treated with magnesium (61). The most recent systematic review of 26 clinical trials, including 73,363 patients, concluded that IV magnesium likely does not reduce mortality following MI and thus should not be utilized as a treatment (62). Thus, the use of IV magnesium sulfate in the therapy of acute MI remains controversial.
Vascular endothelial cells line arterial walls where they are in contact with the blood that flows through the circulatory system. Normally functioning vascular endothelium promotes vasodilation when needed, for example, during exercise, and inhibits the formation of blood clots. Conversely, endothelial dysfunction results in widespread vasoconstriction and coagulation abnormalities. In cardiovascular disease, chronic inflammation is associated with the formation of atherosclerotic plaques in arteries. Atherosclerosis impairs normal endothelial function, increasing the risk of vasoconstriction and clot formation, which may lead to heart attack or stroke (reviewed in 63). Research studies have indicated that pharmacologic doses of oral magnesium may improve endothelial function in individuals with cardiovascular disease. A randomized, double-blind, placebo-controlled trial in 50 men and women with stable coronary artery disease found that six months of oral magnesium supplementation (730 mg/day) resulted in a 12% improvement in flow-mediated vasodilation compared to placebo (64). In other words, the normal dilation response of the brachial (arm) artery to increased blood flow was improved. 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 platelet aggregation), three months of oral magnesium supplementation (800 to 1,200 mg/day) resulted in an average 35% reduction in platelet-dependent thrombosis, a measure of the propensity of blood to clot (65). Additionally, a study in 657 women participating in the Nurses' Health Study reported that dietary magnesium intake was inversely associated with E-selectin, a marker of endothelial dysfunction (66). In vitro studies using human endothelial cells have provided mechanistic insights into the association of low magnesium concentrations, chronic inflammation, and endothelial dysfunction (67). Finally, since magnesium can function as a calcium antagonist, it has been suggested that it could be utilized to slow down or reverse the calcification of vessels observed in patients with chronic kidney disease. The atherosclerotic process is often accelerated in these subjects, and patients with chronic kidney disease have higher rates of cardiovascular-related mortality compared to the general population (68). Additional studies are needed to assess whether magnesium may be of benefit in improving endothelial function in individuals at high risk for cardiovascular diseases.
Magnesium depletion is commonly associated with both insulin-dependent (type 1) and non-insulin dependent (type 2) diabetes mellitus. Reduced serum levels of magnesium (hypomagnesemia) have been reported in 13.5% to 47.7% of individuals with type 2 diabetes (69). 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 increase insulin resistance in a few studies and may adversely affect blood glucose control in diabetes (70). One study reported that dietary magnesium supplements (390 mg/day of elemental magnesium for four weeks) improved glucose tolerance in elderly individuals (71). Another small study in nine patients with type 2 diabetes reported that supplemental magnesium (300 mg/day for 30 days), in the form of a liquid, magnesium-containing salt solution, improved fasting insulin levels but did not affect fasting glucose levels (72). Yet, the most recent meta-analysis of nine randomized, double-blind, controlled trials concluded that oral supplemental magnesium may lower fasting plasma glucose levels in individuals with diabetes (73). One randomized, double-blind, placebo-controlled study in 63 individuals with type 2 diabetes and hypomagnesemia found that those taking an oral magnesium chloride solution (638 mg/day of elemental magnesium) for 16 weeks had improved measures of insulin sensitivity and glycemic control compared to those taking a placebo (74). Large-scale, well-controlled studies are needed to determine whether magnesium supplementation has any long-term therapeutic benefit in patients with type 2 diabetes. However, correcting existing magnesium deficiencies may improve glucose metabolism and insulin sensitivity in those with diabetes.
Individuals who suffer from recurrent migraine headaches have lower intracellular magnesium levels (demonstrated in both red blood cells and white blood cells) than individuals who do not experience migraines (75). Additionally, the incidence of ionized magnesium deficiency has been found to be higher in women with menstrual migraine compared to women who don't experience migraines with menstruation (76). 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 early placebo-controlled trials demonstrated modest decreases in the frequency of migraine headaches after supplementation with 600 mg/day of magnesium (75, 77). Another placebo-controlled trial in 86 children with frequent migraine headaches found that oral magnesium oxide (9 mg/kg body weight/day) reduced headache frequency over the 16-week intervention (78). However, there was no reduction in the frequency of migraine headaches with 485 mg/day of magnesium in another placebo-controlled study conducted in 69 adults suffering migraine attacks (79). The efficiency of magnesium absorption varies with the type of oral magnesium complex, and this might explain the conflicting results. Although no serious adverse effects were noted during these migraine headache trials, 19% to 40% of individuals taking the magnesium supplements have reported diarrhea and gastric (stomach) irritation.
The efficacy of magnesium infusions was also investigated in a randomized, single-blind, placebo-controlled, cross-over trial of 30 patients with migraine headaches (80). The administration of 1 gram of intravenous (IV) magnesium sulfate ended the attacks, abolished associated symptoms, and prevented recurrence within 24 hours in nearly 90% of the subjects. While this promising result was confirmed in another trial (81), two additional randomized, placebo-controlled studies found that magnesium sulfate was less effective than other molecules (e.g., metoclopramide) in treating migraines (82, 83). The most recent meta-analysis of five randomized, double-blind, controlled trials reported no beneficial effect of IV magnesium for migraine in adults (84). However, the effect of magnesium should be examined in larger studies targeting primarily migraine sufferers with hypomagnesemia (85).
The occurrence of hypomagnesemia may be greater in patients with asthma than in individuals without asthma (86). Several clinical trials have examined the effect of intravenous (IV) magnesium infusions on acute asthmatic attacks. One double-blind, placebo-controlled trial in 38 adults with acute asthma, who did not respond to initial treatment in the emergency room, found improved lung function and decreased likelihood of hospitalization when IV magnesium sulfate was infused compared to a placebo (87). However, another placebo-controlled, double-blind study in 48 adults reported that IV infusion of magnesium sulfate did not improve lung function in patients experiencing an acute asthma attack (88). A systematic review of seven randomized controlled trials (five adult and two pediatric) concluded that IV magnesium sulfate is beneficial in patients with severe, acute asthma (89). In addition, a meta-analysis of five randomized placebo-controlled trials, involving 182 children with severe asthma, found that IV infusion of magnesium sulfate was associated with a 71% reduction in the need for hospitalization (90). In the most recent meta-analysis of 16 randomized controlled trials (11 adult and 5 pediatric), IV magnesium sulfate treatment was associated with a significant improvement of respiratory function in both adults and children with acute asthma treated with beta-2-agonists and systemic steroids (91). At present, available evidence indicates that IV 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 (92-94). Nebulized, inhaled magnesium for treating asthma requires further investigation. A meta-analysis of eight randomized controlled trials in asthmatic adults showed that nebulized, inhaled magnesium sulfate had benefits with respect to improved lung function and decreased hospital admissions (91). However, a recent systematic review of 16 randomized controlled trials, including adults, children, or both, found little evidence that inhaled magnesium sulfate, along with a beta-2-agonist, improved pulmonary function in patients with acute asthma (95).
A large US national survey indicated that average magnesium intake is about 350 mg/day for men and about 260 mg/day for women—significantly below the current recommended dietary allowance (RDA). Magnesium intakes were even lower in men and women over 50 years of age (8). Such findings suggest that marginal magnesium deficiency may be relatively common in the US.
Since magnesium is part of chlorophyll, the green pigment in plants, green leafy vegetables are rich in magnesium. Unrefined grains (whole grains) and nuts also have high magnesium content. Meats and milk have an intermediate content of magnesium, while refined foods generally have the lowest. Water is a variable source of intake; harder water usually has a higher concentration of magnesium salts (2). Some foods that are relatively rich in magnesium are listed in the table below along with their magnesium content in milligrams (mg). For more information on the nutrient content of foods, search the USDA food composition database.
|Cereal, all bran||½ cup||112|
|Cereal, oat bran||½ cup dry||96|
|Brown rice, medium-grain, cooked||1 cup||86|
|Fish, mackerel, cooked||3 ounces||82|
|Spinach, frozen, chopped, cooked||½ cup||78|
|Almonds||1 ounce (23 almonds)||77|
|Swiss chard, chopped, cooked||½ cup||75|
|Lima beans, large, immature seeds, cooked||½ cup||63|
|Cereal, shredded wheat||2 biscuits||61|
|Molasses, blackstrap||1 tablespoon||48|
|Hazelnuts||1 ounce (21 hazelnuts)||46|
|Okra, frozen, cooked||½ cup||37|
|Milk, 1% fat||8 fluid ounces||34|
Magnesium supplements are available as magnesium oxide, magnesium gluconate, magnesium chloride, and magnesium citrate salts, as well as a number of amino acid chelates, including magnesium aspartate. Magnesium hydroxide is used as an ingredient in several antacids (96).
Adverse effects have not been identified from magnesium occurring naturally in food. However, adverse effects from excess magnesium have been observed with intakes of various magnesium salts (i.e., supplemental magnesium) (6). The initial symptom of excess magnesium supplementation is diarrhea—a well-known side effect of magnesium that is used therapeutically as a laxative. Individuals with impaired kidney function are at higher risk for adverse effects of magnesium supplementation, and symptoms of magnesium toxicity have occurred in people with impaired kidney function taking moderate doses of magnesium-containing laxatives or antacids. Elevated serum levels of magnesium (hypermagnesemia) may result in a fall in blood pressure (hypotension). Some of the later effects of magnesium toxicity, such as lethargy, confusion, disturbances in normal cardiac rhythm, and deterioration of kidney function, are related to severe hypotension. As hypermagnesemia progresses, muscle weakness and difficulty breathing may occur. Severe hypermagnesemia may result in cardiac arrest (2, 3). The Food and Nutrition Board (FNB) of the Institute of Medicine set the tolerable upper intake level (UL) for magnesium at 350 mg/day. This UL represents the highest level of daily supplemental magnesium intake likely to pose no risk of diarrhea or gastrointestinal disturbance in almost all individuals. The FNB cautions that individuals with renal impairment are at higher risk for adverse effects from excess supplemental magnesium intake. However, the FNB also notes that there are some conditions that may warrant higher doses of magnesium under medical supervision (2).
Tolerable Upper Intake Level (UL) for Supplemental Magnesium
|Age Group||UL (mg/day)|
|Infants 0-12 months||Not possible to establish*|
|Children 1-3 years||65|
|Children 4-8 years||110|
|Children 9-13 years||350|
|Adolescents 14-18 years||350|
|Adults 19 years and older||350|
*Source of intake should be from food and formula only.
Magnesium interferes with the absorption of digoxin (a heart medication), nitrofurantoin (an antibiotic), and certain anti-malarial drugs, which could potentially reduce drug efficacy. Bisphosphonates (e.g., alendronate and etidronate), which are drugs used to treat osteoporosis, and magnesium should be taken two hours apart so that the absorption of the bisphosphonate is not inhibited. Magnesium has also been found to reduce the efficacy of chlorpromazine (a tranquilizer), penicillamine, oral anticoagulants, and the quinolone and tetracycline classes of antibiotics. Because intravenous magnesium has increased the effects of certain muscle-relaxing medications used during anesthesia, it is advisable to let medical staff know if you are taking oral magnesium supplements, laxatives, or antacids prior to surgical procedures. High doses of furosemide (Lasix) and some thiazide diuretics (e.g., hydrochlorothiazide), if taken for extended periods, may result in magnesium depletion (96, 97). Moreover, long-term use (three months or longer) of proton-pump inhibitors (drugs used to reduce the amount of stomach acid) may increase the risk of hypomagnesemia (98, 99). Many other medications may also result in renal magnesium loss (3).
The Linus Pauling Institute supports the latest RDA for magnesium intake (400-420 mg/day for men and 310-320 mg/day for women). Following the Linus Pauling Institute recommendation to take a daily multivitamin/mineral supplement may ensure an intake of at least 100 mg of magnesium/day. Few multivitamin/mineral supplements contain more than 100 mg of magnesium due to its bulk. Because magnesium is plentiful in foods, eating a varied diet that provides green vegetables, whole grains, and nuts daily should provide the rest of an individual's magnesium requirement.
Older adults (> 50 years)
Older adults are less likely than younger adults to consume enough magnesium to meet their needs and should therefore take care to eat magnesium-rich foods in addition to taking a multivitamin/mineral supplement daily. Since older adults are more likely to have impaired kidney function, they should avoid taking more than 350 mg/day of supplemental magnesium without medical consultation (see Safety).
Written in April 2003 by:
Jane Higdon, Ph.D.
Linus Pauling Institute
Oregon State University
Updated in October 2013 by:
Barbara Delage, Ph.D.
Linus Pauling Institute
Oregon State University
Reviewed in May 2014 by:
Stella L. Volpe, Ph.D., R.D., L.D.N., F.A.C.S.M.
Professor and Chair
Department of Nutrition Sciences
Copyright 2001-2015 Linus Pauling Institute
The Linus Pauling Institute Micronutrient Information Center provides scientific information on the health aspects of dietary factors and supplements, foods, and beverages for the general public. The information is made available with the understanding that the author and publisher are not providing medical, psychological, or nutritional counseling services on this site. The information should not be used in place of a consultation with a competent health care or nutrition professional.
The information on dietary factors and supplements, foods, and beverages contained on this Web site does not cover all possible uses, actions, precautions, side effects, and interactions. It is not intended as nutritional or medical advice for individual problems. Liability for individual actions or omissions based upon the contents of this site is expressly disclaimed.
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