Herbs & Supplements:
Magnesium
Supplement Forms / Alternate Names
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Magnesium Sulfate, Magnesium Gluconate, Magnesium Fumarate, Magnesium Citrate, Magnesium Malate, Magnesium Oxide, Magnesium Chloride
Principal Proposed Uses
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Migraine Headaches, Noise-Related Hearing Loss, Kidney Stones, Hypertension (High Blood Pressure), Coronary Artery Disease
Other Proposed Uses
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Atherosclerosis, Painful Menstruation (Dysmenorrhea), PMS, Restless Legs Syndrome, Diabetes, Osteoporosis, Low Blood Sugar, Glaucoma, Fibromyalgia, Fatigue, Stroke, Low HDL ("Good") Cholesterol, Autism, Pregnancy-Induced Leg Cramps, Various Forms of Heart Disease, Mitral Valve Prolapse, Congestive Heart Failure, Asthma
Magnesium is an essential nutrient, meaning that your body needs it for healthy functioning. It is found in significant quantities throughout the body and used for numerous purposes, including muscle relaxation, blood clotting, and the manufacture of ATP (adenosine triphosphate, the body's main energy molecule).
It has been called "nature's calcium channel–blocker." The idea refers to magnesium's ability to block calcium from entering muscle and heart cells. A group of prescription heart medications work in a similar way, although much more powerfully. This may be the basis for magnesium's effects on migraine headaches and high blood pressure.
Magnesium is one of the few essential nutrients for which deficiencies are fairly common. For this reason, it is probably reasonable for most people to take magnesium on general principle, regardless of particular therapeutic use.
Requirements/Sources
Requirements for magnesium increase as we grow and age. The official U.S. and Canadian recommendations for daily intake are as follows:
- Infants 0–6 months, 30 mg
7–12 months, 75 mg - Children 1–3 years, 80 mg
4–8 years, 130 mg - Males 9–13 years, 240 mg
14–18 years, 410 mg
19–30 years, 400 mg
31 years and older, 420 mg - Females 9–13 years, 240 mg
14–18 years, 360 mg
19–30 years, 310 mg
31 years and older, 320 mg - Pregnant women 18 years and younger, 400 mg
19–30 years, 350 mg
31–50 years, 360 mg - Nursing women 18 years and younger, 360 mg
19–30 years, 310 mg
31–50 years, 320 mg
NOTE: These recommendations refer to total intake from food plus supplements. For supplements alone, the U.S. government has set the following upper intake limits:
- Children 1-3 years, 65 mg
- Children 4-8 years, 110 mg
- Adults, 350 mg
- Pregnant or nursing women, 350 mg
In the United States, the average dietary intake of magnesium is significantly lower than the recommended daily allowance, although whether this truly indicates deficiency is unclear.1,2 Alcohol abuse, surgery, diabetes, zinc supplements, certain types of diuretics (thiazide and loop diuretics, but not potassium-sparing diuretics), estrogen and oral contraceptives, and the medications cisplatin and cyclosporin have been reported to reduce your body's level of magnesium or increase magnesium requirements.3,4,5,88-92 If you are taking potassium or manganese, you may need extra magnesium as well.6,7
While it is sometimes said that calcium interferes with magnesium absorption, it apparently has no significant effect on overall magnesium status.8,9
The heart drug digoxin (digitalis) does not interfere with magnesium levels in the body; however, low magnesium levels can increase the risk or heart arrhythmias caused by the medication.93-95 Since many people on digitalis also take loop diuretics (which can lower magnesium levels), magnesium deficiency is a real possibility.
Kelp is very high in magnesium, as are wheat bran, wheat germ, almonds, and cashews. Other good sources include blackstrap molasses, brewer's yeast (not to be confused with nutritional yeast), buckwheat, and nuts and whole grains. You can also get appreciable amounts of magnesium from collard greens, dandelion greens, avocado, sweet corn, Cheddar cheese, sunflower seeds, shrimp, dried fruit (figs, apricots, and prunes), and many other common fruits and vegetables.
Therapeutic Dosages
A typical supplemental dosage of magnesium ranges from the nutritional needs described above to as high as 600 mg daily. For premenstrual syndrome (PMS) and dysmenorrhea (painful menstruation), an alternative approach is to start taking 500 to 1,000 mg daily, beginning on day 15 of the menstrual cycle and continuing until menstruation begins.
Therapeutic Uses
Several preliminary studies suggest that regular use of magnesium can help prevent migraine headaches.10,11,12
Magnesium may also be useful for protecting the ears against hearing loss caused by exposure to loud noises,13 reducing the incidence of kidney stones,14 and perhaps improving blood pressure15,16,17 and preventing or treating coronary artery disease.18,19 There is also some evidence that magnesium may decrease the atherosclerosis risk caused by hydrogenated oils, margarine-like fats found in many "junk" foods.20
Preliminary double-blind trials suggest that magnesium may be useful for dysmenorrhea (menstrual cramps)21,22 and symptoms of PMS (premenstrual syndrome), including menstrual migraines.23,24 Open trials suggest that magnesium might decrease symptoms of restless legs syndrome. 25,26 Although there is no direct evidence that magnesium helps people with diabetes, such individuals are known to be deficient in magnesium,27,28,29 and magnesium supplementation may be a good idea on general principle. (However, individuals with severe kidney disease should take magnesium supplements only on their physician's advice.)
Magnesium has also been suggested as a treatment for osteoporosis, low blood sugar, glaucoma, fibromyalgia, fatigue, stroke, low HDL ("good") cholesterol, Alzheimer's disease, angina, attention deficit disorder, periodontal disease, rheumatoid arthritis, and various forms of heart disease including mitral valve prolapse and congestive heart failure. However, there is little to no real evidence that it is effective for these purposes.
An interesting series of studies suggests (but certainly doesn't prove) that the combination of vitamin B6 and magnesium can be helpful in autism.30–40
One double-blind trial suggests that magnesium is helpful for pregnancy-induced leg cramps.41
Alternative medicine literature frequently mentions magnesium as a treatment for asthma. However, this idea seems to be based entirely on the use of intravenous magnesium as an emergency treatment for asthma. When you take something by mouth, it's a very different matter from having it injected into your veins. There is no real evidence that oral magnesium helps asthma, and even some evidence that it does not help.42
Warning: Do not self-inject magnesium! See your doctor for such treatment.
Although magnesium is sometimes mentioned as a treatment to help keep the heart beating normally, a 6-month double-blind trial of 170 people did not find it effective for preventing a particular heart rhythm abnormality called atrial fibrillation.43
Studies on magnesium supplements for improving strength of sports performance have returned contradictory results.44–51
Finally, magnesium supplements have been suggested for reducing complications of pregnancy such as preeclampsia, but the results of large double-blind trials have been mixed.52,53 It may be that magnesium is only helpful for this purpose in populations with particularly significant magnesium deficiency.
What Is the Scientific Evidence for Magnesium?
Migraine Headaches
A double-blind study found that regular use of magnesium helps prevent migraine headaches. In this 12-week trial, 81 people with recurrent migraines were given either 600 mg of magnesium daily or placebo.54 By the last 3 weeks of the study, the treated group's migraines had been reduced by 41.6%, compared to a reduction of 15.8% in the placebo group. The only side effects observed were diarrhea (in about one-fifth of the participants) and, less often, digestive irritation.
Similar results have been seen in other smaller double-blind studies.55,56 One study found no benefit,57 but it has been criticized on many significant points, including using an excessively strict definition of what constituted benefit.58
Noise-Related Hearing Loss
One double-blind placebo-controlled study on 300 military recruits suggests that 167 mg of magnesium daily can prevent hearing loss due to exposure to high-volume noise.59
Kidney Stones
Magnesium inhibits the growth of calcium oxalate stones in the test tube60 and decreases stone formation in rats.61 However, human studies have had mixed results. In one 2-year open study, 56 people taking magnesium hydroxide had fewer recurrences of kidney stones than 34 people not given magnesium.62 In contrast, a double-blind (and, hence, more reliable) study of 124 individuals found that magnesium hydroxide was essentially no more effective than placebo.63
Hypertension (High Blood Pressure)
Magnesium works with calcium and potassium to regulate blood pressure. Several studies suggest that magnesium supplements can reduce blood pressure in people with hypertension,64–67 although some have not.
Coronary Artery Disease
A double-blind placebo-controlled trial of 50 individuals with blockage in the arteries to the heart (coronary artery disease) found that supplementation with magnesium at 730 mg daily significantly improved exercise tolerance.68
In addition, a double-blind study of 42 individuals with heart disease found that magnesium supplements reduced the tendency of the body to form blood clots.69
Dysmenorrhea
A 6-month double-blind placebo-controlled study of 50 women with menstrual pain found that treatment with magnesium significantly improved symptoms.70 The researchers reported evidence of reduced levels of prostaglandin F2 alpha, a hormone-like substance involved in pain and inflammation.
Similarly positive results were seen in a double-blind placebo-controlled study of 21 women.71
PMS Symptoms
A double-blind placebo-controlled study of 32 women found that magnesium taken from day 15 of the menstrual cycle to the onset of menstrual flow could significantly improve premenstrual mood changes.72
Another small double-blind preliminary study found that regular use of magnesium could reduce symptoms of PMS-related fluid retention.73 In this study, 38 women were given magnesium or placebo for 2 months. The results showed no effect after one cycle, but by the end of two cycles, magnesium significantly reduced weight gain, swelling of extremities, breast tenderness and abdominal bloating.
In addition, one small double-blind study (20 participants) found that magnesium supplementation can help prevent menstrual migraines.74
Preliminary evidence suggests that the combination of magnesium and vitamin B6 might be more effective than either treatment alone.75
Autism
Six double-blind placebo-controlled trials enrolling a total of about 150 children have evaluated the effects of vitamin B6 and magnesium combination therapy for autism.76–81 All of these studies found a significant improvement in autistic behaviors. However, the study design used in many of these trials was rather complicated and difficult to evaluate. For example, the largest trial (actually, a series of four closely intertwined trials) involved multiple groups of participants taking different treatments with inadequate time in between for the vitamins and minerals to wash out.82 These studies were marked by other flaws as well; in addition, they were all performed by one research group.
For these reasons, until better-designed trials reported by independent laboratories are published, this therapy cannot be considered proven.
Pregnancy-Induced Leg Cramps
Pregnant women frequently experience painful leg cramping. One double-blind trial of 73 pregnant women found that 3 weeks of magnesium supplements significantly reduced leg cramps as compared to placebo.83
Safety Issues
In general, magnesium appears to be quite safe when taken at recommended dosages. The most common complaint is loose stools. However, people with severe kidney or heart disease should not take magnesium (or any other supplement) except on the advice of a physician. Maximum safe dosages have not been established for young children. There has been one case of death caused by excessive use of magnesium supplements in a developmentally and physically disabled child.84 Pregnant or nursing women should not exceed the nutritional dosages presented under Requirements/Sources.
If taken at the same time, magnesium can interfere with the absorption of antibiotics in the tetracycline family,85 and, possibly, the drug nitrofurantoin.96 Also, when combined with oral diabetes drugs in the sulfonylurea family (Tolinase, Micronase, Orinase, Glucotrol, Diabinese, DiaBeta), magnesium may cause blood sugar levels to fall more than expected.86
Interactions You Should Know About
If you are taking
View References
Last reviewed May 2002 by Medical Review Board
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