Overview
Magnesium is an essential nutrient, meaning that the 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).
Magnesium has been called nature’s calcium channel blocker because of its 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 some of magnesium’s effects when it is taken as a supplement in fairly high doses.
Requirements and Sources
Requirements for magnesium increase as people grow and age. The official U.S. and Canadian recommendations for daily intake are as follows: 30 milligrams (mg) for infants up to six months old, 75 mg for infants seven to twelve months old, 80 mg for children one to three years old, 130 mg for children four to eight years old, and 240 mg for persons nine to thirteen years old. For those fourteen to eighteen years old, the recommendations are 410 mg for males and 360 mg for females; for those nineteen to thirty years old, 400 mg for males and 310 for females; and for those aged thirty-one and over, 420 mg for males and 320 mg for women. The recommendations for pregnant women are 400 mg for those eighteen and younger, 350 mg for those nineteen to thirty years old, and 360 mg for those thirty-one to fifty years old; for nursing women, they are 360 mg for those aged eighteen and younger, 310 mg for those nineteen to thirty, and 320 mg for those thirty-one to fifty years old.
These recommendations refer to total intake from food plus supplements. The
average diet provides a daily intake of magnesium very close to these amounts. In
the United States, the average dietary intake of magnesium is lower than the
recommended daily allowance; however, it is unclear whether this truly indicates
deficiency, or if the recommended allowance is too high. 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 the body’s level of magnesium or increase
magnesium requirements. Those taking potassium supplements may receive
greater benefit from them if they take extra magnesium as well. While it is
sometimes said that calcium interferes with magnesium absorption, this effect is
apparently too small to have a significant effect on overall magnesium status.
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, nuts, and
whole grains. One 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 from 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 fifteen of the menstrual cycle and continuing until menstruation begins. Magnesium citrate may be slightly more absorbable than other forms of magnesium.
Therapeutic Uses
Preliminary double-blind studies suggest that regular use of magnesium supplements may help prevent migraine headaches, hearing loss caused by exposure to loud noises, and kidney stones and may help treat high blood pressure, angina, dysmenorrhea (menstrual cramps), pregnancy-induced leg cramps, and premenstrual syndrome (including menstrual migraines).
People with diabetes are often deficient in magnesium, and according to some (but not all) studies, magnesium supplementation may enhance blood sugar control and insulin sensitivity in people with diabetes or prediabetic conditions. Magnesium may also help control blood pressure in people with both hypertension and diabetes.
One study found that magnesium supplements might be helpful for people with mitral valve prolapse who also have low levels of magnesium in the blood. There is some evidence that magnesium may decrease the atherosclerosis risk caused by hydrogenated oils, the margarine-like fats found in many junk foods.
Magnesium supplements do not appear to be helpful for preventing preeclampsia. (Magnesium, taken by injection rather than orally, however, is probably helpful for treating preeclampsia that already exists.)
Magnesium is sometimes said to decrease symptoms of restless legs syndrome, but the evidence that it works consists solely of open trials without a placebo group, and such studies are not trustworthy. Weak evidence hints at possible benefits for insomnia.
It is often said that magnesium supplements are essential for preventing or treating osteoporosis, but there is only minimal supporting evidence for this claim. Studies on magnesium supplements for improving sports performance have returned contradictory results.
Magnesium has also been suggested as a treatment for Alzheimer’s disease, attention deficit disorder, fatigue, fibromyalgia, low high-density lipoproteins (HDL, or good cholesterol), periodontal disease, rheumatoid arthritis, and stroke. However, there is virtually no evidence that it is helpful for any of these conditions. Despite some early enthusiasm, combination therapy with vitamin B6 and magnesium has not been found helpful in autism. One double-blind, placebo-controlled study failed to find magnesium helpful in glaucoma.
Magnesium is sometimes advocated for stabilizing the heart after a heart attack, but one study actually found that use of magnesium slightly increased risk of sudden death, repeat heart attack, or need for bypass surgery in the year following the initial heart attack. However, magnesium may be helpful in congestive heart failure. In a well-designed trial involving seventy-nine patients with severe congestive heart failure, magnesium (as magnesium orotate) significantly improved survival and clinical symptoms after one year compared with a placebo.
Alternative medical literature frequently mentions magnesium as a treatment for asthma. However, this idea seems to be based primarily on the use of intravenous magnesium as an emergency treatment for asthma. Taking something by mouth is very different from having it injected into the veins. Studies of oral magnesium for asthma have shown more negative than positive results. Inhaled, aerosolized magnesium, however, has shown some promise.
Although magnesium is sometimes mentioned as a treatment to help keep the heart
beating normally, a six-month double-blind trial of 170 people did not find it
effective for preventing a particular heart rhythm abnormality called
atrial
fibrillation. However, a small double-blind,
placebo-controlled trial found that magnesium supplements reduced episodes of
arrhythmia in individuals with congestive heart failure (CHF). One possible
explanation: People with congestive heart failure often take drugs (loop
diuretics) that deplete magnesium. The combination of magnesium deficiency with
digoxin (another drug given for CHF) may cause
arrhythmias. Thus, it is possible that the benefits seen
here were caused by correction of that depletion.
Scientific Evidence
Migraine headaches. A double-blind study found that regular use
of magnesium helps prevent migraine headaches. In this twelve-week
trial, eighty-one people with recurrent migraines were given either 600 mg of
magnesium daily or a placebo. By the last three weeks of the study, the treated
group’s migraines had been reduced by 41.6 percent, compared with a reduction of
15.8 percent 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. One study found no benefit, but it has been criticized on many significant points, including using an excessively strict definition of what constituted benefit.
Noise-related hearing loss. One double-blind, placebo-controlled study on three hundred military recruits suggests that 167 mg of magnesium daily can prevent hearing loss due to exposure to high-volume noise.
Kidney stones. Magnesium inhibits the growth of calcium oxalate
stones in the test tube and decreases stone formation in rats. However, human
studies have had mixed results. In one two-year open study, 56 people taking
magnesium hydroxide had fewer recurrences of kidney stones
than 34 people not given magnesium. In contrast, a double-blind (and, hence, more
reliable) study of 124 people found that magnesium hydroxide was essentially no
more effective than a placebo.
Hypertension. Magnesium works with calcium and potassium to
regulate blood pressure. Several studies suggest that magnesium supplements can
reduce blood pressure in people with hypertension, although some studies
have not shown this.
In one study, eighty-two people (ages forty to seventy-five years) with diabetes, high blood pressure, and low levels of magnesium were randomized to receive 2.5 g of magnesium chloride or a placebo for four months. Those in the treatment group had lower blood pressure readings compared with those in the control group.
Angina. In a double-blind, placebo-controlled trial of 187 people
with angina, six months of treatment with magnesium at a dose of
730 mg daily improved exercise tolerance and enhanced overall quality of life.
Benefits were also seen in a similar, smaller double-blind trial.
After a heart attack. In a one-year double-blind, placebo-controlled trial of 468 individuals who had just experienced a heart attack, use of a magnesium supplement at a dose of 360 mg daily failed to prevent heart-related events (defined as heart attack, sudden cardiac death, or need for cardiac bypass) and actually may have increased the risk slightly.
Dysmenorrhea. A six-month double-blind, placebo-controlled study of fifty women with menstrual pain found that treatment with magnesium significantly improved symptoms. The researchers reported evidence of reduced levels of prostaglandin F 2 alpha, a hormone-like substance involved in pain and inflammation. Similarly positive results were seen in a double-blind, placebo-controlled study of twenty-one women.
Premenstrual syndrome (PMS). A double-blind, placebo-controlled study of thirty-two women found that magnesium taken from day fifteen of the menstrual cycle to the onset of menstrual flow could significantly improve PMS symptoms, specifically mood changes.
Another small, double-blind preliminary study found that regular use of magnesium could reduce symptoms of PMS-related fluid retention. In this study, thirty-eight women were given magnesium or placebo for two 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 (twenty participants) found that magnesium supplementation can help prevent menstrual migraines. Preliminary evidence suggests that the combination of magnesium and vitamin B6 might be more effective than either treatment alone.
Pregnancy-induced leg cramps. Pregnant women frequently experience painful leg cramping. One double-blind trial of seventy-three pregnant women found that three weeks of magnesium supplements significantly reduced leg cramps compared with a placebo.
Safety Issues
The U.S. government has set the following upper limits for use of magnesium supplements: 65 mg for children aged one to three, 110 mg for children four to eight, 350 mg for adults, and 350 mg for pregnant or nursing women. In general, magnesium appears to be quite safe when taken at or below 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 children of all ages. There has been one case of death caused by excessive use of magnesium supplements in a developmentally and physically disabled child. Pregnant or nursing women should not exceed the nutritional dosages presented in the Requirements and Sources section.
If taken at the same time, magnesium can interfere with the absorption of
antibiotics in the tetracycline family and, possibly of
the drug nitrofurantoin. Also, when combined with oral diabetes drugs
in the sulfonylurea family, magnesium may cause blood sugar levels to fall more
than expected.
Important Interactions
Persons taking potassium supplements, manganese, loop and thiazide diuretics,
oral contraceptives, estrogen replacement therapy, cisplatin, digoxin, or
medications that reduce stomach acid may need extra magnesium. Persons taking
antibiotics in the tetracycline family or nitrofurantoin (Macrodantin) should
separate their magnesium dose from doses of these medications by at least two
hours to avoid absorption problems. Those taking oral diabetes medications in the
sulfonylurea family (Tolinase, Micronase, Orinase, Glucotrol, Diabinese, DiaBeta)
should work closely with their physicians when taking magnesium to avoid
hypoglycemia. Those taking amiloride should not take
magnesium supplements except on medical advice.
Bibliography
Guerrero-Romero, F., and M. Rodríguez-Morán. “The Effect of Lowering Blood Pressure by Magnesium Supplementation in Diabetic Hypertensive Adults with Low Serum Magnesium Levels.” Journal of Human Hypertension 23, no. 4 (2009): 245-251.
Hatzistavri, L. S., et al. “Oral Magnesium Supplementation Reduces Ambulatory Blood Pressure in Patients with Mild Hypertension.” American Journal of Hypertension 22, no. 10 (2009): 1070-1075.
Kazaks, A. G., et al. “Effect of Oral Magnesium Supplementation on Measures of Airway Resistance and Subjective Assessment of Asthma Control and Quality of Life in Men and Women with Mild to Moderate Asthma.” Journal of Asthma 47, no. 1 (2010): 83-92.
Stepura, O. B., and A. I. Martynow. “Magnesium Orotate in Severe Congestive Heart Failure (MACH).” International Journal of Cardiology 134, no. 1 (2009): 145-147.
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