MAGNESIUM

What about people whose blood pressure is already high? Could magnesium supplements help them?

Since 1985, at least 16 trials have given magnesium to people with high or high-normal blood pressure. The two largest compared 360 mg a day to a (look-alike but magnesium-free) placebo in 285 people for six months.(7,8)

"Magnesium had no effect in either," says Frank Sacks of the Harvard School of Public Health in Boston, who headed one of the two studies.

Still, some smaller studies have found that magnesium lowered blood pressure modestly. In the latest, from Japan, 360 mg a day for eight weeks lowered blood pressure by an average of 3 points over 1 point in 60 men and women who started with high-normal blood pressures (they averaged 134/81).(9)

"Extra magnesium is not a definitive treatment for high blood pressure," says Marvin Moser, a hypertension expert at Yale University. "Eating magnesium-rich foods or taking magnesium supplements might result in some decrease in pressure. But the vast majority of people with high blood pressure will still need medication."

Heart Disease & Stroke

Since the 1960s, researchers have known that people who live in areas where the water is "hard" often have lower rates of heart disease and stroke. ("Hard" water contains more calcium, magnesium, and other minerals than "soft" water.)

But the amount of magnesium in hard water is typically no more than 3 mg to 20 mg per liter--less than ten percent of what people get from a day's food.

"It's hard to imagine how such a small amount could have such a big effect on preventing heart disease," says epidemiologist Raymond Neutra of the California Department of Health Services.

"Still, there's enough suggestive evidence out there that it needs to be seriously looked at."

In fact, there's some evidence that magnesium may be harmful. In what Neutra calls a "sobering" Dutch study from the early 1990s, more than 450 men and women with heart disease who were given 360 mg a day of magnesium for a year were more likely to suffer a second heart attack, need a bypass, or die a sudden death than heart disease victims who were given a placebo.(10)

"That could be due to chance," says Neutra. Another possibility, according to USC's Robert Rude: People with more severe heart disease may have inadvertently ended up in the group given magnesium.

Other Diseases

* Migraines. "Some people who suffer from migraine headaches may be deficient in magnesium," says Alexander Mauskop of the New York Headache Clinic.

In one of two small studies, 40 migraine patients who took 600 mg of magnesium a day for 12 weeks went from three attacks per month to two. Patients taking a placebo had no fewer attacks. There was no difference in the severity of the headaches, though.(11)

* Osteoporosis. "There are hints out there in human and animal research that magnesium is important for good quality bones," says Purdue University's Connie Weaver. "But the evidence that magnesium supplements can prevent osteoporosis in humans is pretty skimpy."