Magnesium: We don't appear to be getting enough

Janet Raloff

Mention magnesium, and many people conjure up images of a hard, silvery alloy used to fashion parts for aircraft and automobiles, or machinery that needs to resist corrosion. Yet, the human body also finds myriad uses for this important mineral.

Some 350 different enzymes rely on magnesium, notes cardiovascular biologist Burton M. Altura of the State University of New York Health Science Center at Brooklyn. That's more uses than the body makes of any other metal, he observes. Despite a recognition that our cells appear to depend on magnesium, precisely what they do with it remains open to considerable speculation.

And it's not for want of probing. Though many studies have scrutinized the mineral's role in health, most have come away with only fairly general conclusions—leaving veiled the underlying mechanisms.

One such study, appearing in this month's Journal of Clinical Endocrinology and Metabolism, for example, finds that in young men, dietary supplements of magnesium can slow bone turnover, the routine breakdown and rebuilding of bone. They are interested in bone turnover because in postmenopausal women this process can contribute to bone loss and osteoporosis, a crippling embrittlement of bones.

A second study, this one in the August Hypertension, reports that magnesium supplements offer some therapeutic benefit to men with high blood pressure—even those already taking medicine to control their hypertension.

What these studies have in common is a finding that the body benefits from receiving substantially more than the recommended daily allowance (RDA) of this mineral—350 milligrams for most men and 300 mg for most women. So when individuals in these studies were supplemented to receive roughly twice the RDA—and the body didn't discard all the excess in urine but instead appeared to show health improvements—the implication is that the RDA must be too low.

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Blood pressure too high?

In the hypertension trial,Yuhei Kawano and his colleagues at the National Cardiovascular Center in Osaka, Japan, gave supplements containing 480 milligrams of magnesium for 8 weeks to 60 men and women who had high blood pressure. For another 8 weeks, they maintained  their normal diet and took no supplements. Throughout each phase of the trial, blood pressure measurements were taken regularly—not only during visits to a doctor's office but also at home (and even round-the-clock during one phase) while each individual maintained his or her normal activities.

Kawano's group found that although the women's blood pressure remained unchanged throughout the study, all 34 men experienced a small but significant reduction in the blood pressure during the supplementation. They averaged a drop of 2 to 4 millimeters of mercury (mmHg) in their systolic blood pressure and 1.5 to 2 mmHg reduction in diastolic pressure. The average varied according to where the measurements were taken.

Moreover, the Japanese scientists observed that individual reductions tended to be greater than the average for those men who started with the highest blood pressure—even if it was already being treated with drugs.

Small as the observed reductions are, they may still be significant, according to the National High Blood Pressure Education Program. It has reported that "For the general population, a reduction of 3 mmHg in systolic blood pressure would yield 11 percent fewer strokes, 7 percent fewer coronary events, and 5 percent fewer [premature] deaths."

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Boning up on Magnesium

In the other new paper this month, researchers at the University of Graz Medical School in Austria examined the ability of magnesium supplements to slow bone turnover in healthy young men. Not only did they report success (SN: 8/29/98, p. 134), but they also uncovered some clues to the possible mechanism.

In these 27- to 36-year-olds, the supplementation resulted in lower levels of the active form of magnesium in the blood. Initially, notes K.-H. William Lau, "this was a surprise"—certainly, it ran counter to what had been reported in some other studies. He now suspects that what happened is that the long-term supplementation allowed tissues such as bone a chance to take up a disproportionate share of the biologically active form of the mineral, known as ionized magnesium, from the blood.

Lau told Science News Online that he suspected the reduction in bone turnover may reflect some inhibition of the activity of cells that play a role in the breakdown of bone—normally a common, ongoing process that in healthy people will be followed by a compensatory replacement of this tissue with new bone.

Other scientists who have been investigating magnesium's role in bone health have been exploring different possibilities. For instance, epidemiologist Douglas Kiel at the Hebrew Rehabilitation Center for the Aged in Boston has been collaborating on a trial that is giving supplements of magnesium and potassium to 250 men and 400 women. All are over the age of 70—many in their 90s—and at risk of osteoporotic fractures.

Explains Kiel, as people eat meat, the digestive process liberates some caustic organic acids. Prolonged exposure might allow these agents to eat away at bone, accelerating osteoporosis. "We were going on the assumption that these supplements would neutralize the acids produced as the body breaks down meats."

Whatever the mechanism, Kiel says, their data—due to be published soon—indicate that the supplements indeed are retarding bone loss in these elderly individuals.

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Have a headache?

A few years ago, Altura's team at SUNY-Brooklyn witnessed a therapeutic benefit of magnesium in acute symptoms, such as headache pain.

Because some studies had identified an apparent magnesium deficiency in the brains of persons suffering from migraines—both during headaches and between attacks—Altura's group investigated whether rapid infusions of large amounts of the mineral might ameliorate pain. They administered a solution containing 1 gram of magnesium sulfate intravenously to 40 patients who visited a headache clinic in the throes of moderate to severe pain. They treated not only migraine sufferers but also persons with cluster headaches and chronic daily headaches.

Within 15 minutes, 32 of the men and women—80 percent—experienced relief. Though the headache may not have vanished, the pain lessened by at least 50 percent.

In 18 of these individuals, the pain relief lasted at least 24 hours. Blood tests before treatment confirmed that all but four in this latter group had ionized magnesium concentrations that were lower than the average in a related group of painfree individuals.

Overall, the researchers reported in the March 1996 Headache, "All nine patients with cluster headaches had their acute headache aborted by magnesium therapy." In cluster headaches, considered the most excruciating type (SN: 7/13/91, p. 20), people suffer up to 20 bouts of pain daily in a siege that can last months. For one patient in this trial, a single magnesium infusion ended the cluster. Some of the others received pain relief that lasted 2 to 7 days. Among two whose pain returned full blast within 24 hours, blood tests showed that their ionized magnesium concentrations had remained low. Each subsequent infusion cut the pain for 48 hours.

Migraine sufferers who responded to the treatment experienced a complete alleviation of their current symptoms, including sensitivity to lights and sound. Subsequent studies of additional migraine patients have confirmed a common pattern, Altura says. "Those patients where ionized magnesium in the brain or blood is low will respond to intravenous magnesium very quickly and dramatically."

"Our results support a role for magnesium deficiency in the development of headache," his team concluded.

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Ionized magnesium—there's no predicting it

Ironically, though most of the severe headache sufferers initially had low concentrations of ionized magnesium in their blood, their bodies' total magnesium levels fell within the normal range. Additional studies have shown a similar pattern among other types of patients. For instance, Altura notes, stroke victims with a history of high blood pressure, including diabetic hypertension, "had the lowest level of ionized magnesium when they stroked out." Yet in some cases, their total magnesium concentrations had been within the normal range.

Diet also fails to predict who will tend to have low ionized magnesium concentrations in blood and tissues, Altura has found. In a study 4 years ago, he and his colleagues recruited 18 healthy young men to take different magnesium supplements for 6 days at a time. Although the volunteers had started the trial with normal total-magnesium concentrations—suggesting their diet had contained the RDA of this mineral—a number of the men still had below normal concentrations of the mineral's ionized form. However, once these men were placed on diets containing four to five times the RDA of the mineral, the proportion of ionized magnesium in their blood climbed into the healthy range—despite no change in total magnesium concentrations.

What all this suggests, Altura says, is that whether someone is deficient in the biologically active form of the mineral may not be detectable through measures of total magnesium. Indeed, his data on cardiac cells indicate that if the concentrations of ionized magnesium falls 25 to 40 percent below normal—irrespective of the total amount of magnesium present—magnesium-dependent enzymes no longer function properly.

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Where do we find magnesium?

Perhaps because magnesium plays such important roles in both animals and plants, it shows up in all unprocessed foods. However, much of what we eat is processed, and once lost, magnesium is seldom replenished through intentional food fortification.

To enrich the diet naturally with this mineral, look to nuts, legumes, and unmilled grains. Removing the germ of cereals and the outer seed husks eliminates 80 percent of any magnesium present in the whole grain. Green vegetables and bananas are also relatively good sources of the mineral. You won't find much, however, in other fruits or fish, meat, and milk.

Can you get too much? Except in persons with kidney disease, "there is no evidence that large oral intakes of magnesium are harmful," according to the RDA handbook, published by the National Research Council. However, people can develop diarrhea when they take large quantities of these synthetic forms of the mineral; many supplements provide the mineral in the same oxide form that serves as the basis of common laxatives.

For a natural-foods approach to enriching your diet, check out the Meals For You website on the Internet. It offers a bounty of recipes and will select from its compendium on the basis of magnesium content. Among offerings high on list are grilled fish fillet with lentil salsa at 277 mg, quick chicken chili at 242 mg, tempeh salad at a whopping 370 mg, and steamed spinach at 197 mg.

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Related Readings:

Abraham, G.E., and H. Grewal. 1990. A total dietary program emphasizing magnesium instead of calcium: Effect on the mineral density of calcaneous bone in postmenopausal women on hormonal therapy. Journal of Reproductive Medicine 35(May):503.

Altura, B.T., … and B.M. Altura. 1994. Comparative effects of a Mg-enriched diet and different orally administered magnesium oxide preparations on ionized Mg, Mg metabolism, and electrolytes in serum of human volunteers. Journal of the American College of Nutrition 13(No. 5):447.

H.-P. Dimai, … and K.-H. W. Lau. 1998. Daily oral magnesium supplementation suppresses turnover in young adult males. Journal of Clinical Endocrinology and Metabolism 83(August):2742.

Mauskop, A., … and B.M. Altura. 1996. Intravenous magnesium sulfate rapidly alleviates headaches of various types. Headache 36(March):154.

Raloff, J. 1998. Magnesium: Another metal to bone up on. Science News (Aug. 29):134.

_____. 1991. Hot prospects for quelling cluster headaches. Science News 140(July 13):20.

_____. 1990. Low-magnesium diet may clog heart arteries. Science News 137(April 7):

_____. 1988. New misgivings about low magnesium. Science News 133(June 4):356.

Sojka, J.E., and C.M. Weaver. 1995. Magnesium supplementation and osteoporosis. Nutrition Reviews 53(March):71.

Sources:

Burton M. Altura
Box 31
State University of New York Health Science Center
450 Clarkson Avenue
Brooklyn, NY 11203

Douglas Kiel
Hebrew Rehabilitation Center for the Aged
1200 Centre Street
Boston, MA 02131

K.-H. William Lau
Mineral Metabolism Department
Jerry L. Pettis Memorial Veterans Administration Medical Center
11021 Benton Street
Loma Linda, CA 92357

Meals for You
(recipes on the Web)
WEB: http://www.mymenus.com/

National High Blood Pressure Education Program
National Heart Lung and Blood Institute
National Institutes of Health
P.O. Box 30105
Bethesda, MD 20824-0105
Phone: 301-251-1222
WEB: http://www.nhlbi.nih.gov/

National Osteoporosis Foundation
1150 17th Street, N.W., Suite 500
Washington, DC 20036-4603
Phone: 1-800-464-6700
WEB: http://www.nof.org/

From Science News, Volume 154, No. 10, August 29, 1998.
Copyright ©1998 ScienceService