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MAGNESIUM - nutritional aspects - includes related articles

Nutrition Action Healthletter, Dec, 1998 by David Schardt

You can't take a breath, move a muscle, or think a thought if you don't have enough magnesium in your cells. But according to dietary surveys, many Americans may not be getting enough from their food. And research suggests that a shortage of magnesium may put you at increased risk of diabetes, high blood pressure, heart disease, osteoporosis, and maybe migraines.

Many Americans don't take in enough magnesium to replace what they lose every day. One reason: it's most plentiful in foods like green leafy vegetables, whole grains, beans, and nuts--not exactly staples in most households.

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The National Academy of Sciences (NAS) recommends that women over 30 consume 320 mg of magnesium a day. Yet half of all women aged 31 to 70 get 230 mg or less. Half of all women over 70 get 205 mg or less.

(Those are probably underestimates, because people typically don't report everything they eat.)

The story's the same with men. Most should consume 420 mg a day. But half of all men aged 31 to 50 get less than 330 mg. Half of all men over 70 get less than 275 mg a day.

What's wrong with losing a little magnesium each day?

"Many of us in magnesium research feel that there are harmful consequences to getting less than the requirement--like diabetes, high blood pressure, osteoporosis, and atherosclerosis," says Robert Rude of the University of Southern California in Los Angeles. "But we haven't been able to prove any of that yet."

Rude served as the magnesium expert on the NAS panel that recommended higher magnesium intakes last year.

Others take a more skeptical view. "We don't know which is the cart and which is the horse," says Stephanie Atkinson of McMaster University in Hamilton, Canada, who chaired the panel.

"There is mounting evidence that people with a number of diseases have lower blood magnesium levels, as measured by the only readily available method. But we don't know if that is a result of the disease or a possible cause."

Here's some of that evidence.

Diabetes

Magnesium and insulin need each other. Without magnesium, your pancreas won't secrete enough insulin--or the insulin it secretes won't be efficient enough--to control your blood sugar. And without insulin, magnesium doesn't get transported from your blood into your cells, where it does most of its work.

When Jerry Nadler of the Gonda Diabetes Center at the City of Hope Medical Center in Duarte, California, and his colleagues placed 16 healthy people on magnesium-deficient diets, their insulin became less effective at getting sugar from their blood into their cells, where it's burned or stored as fuel.(1) In other words, they became less insulin sensitive. And that's a step on the road to diabetes.

Two large population studies also found that people who eat less magnesium have a higher risk of type 2, or adult-onset, diabetes. In a study of 65,000 nurses, those who consumed about 220 mg a day were about one-third more likely to develop diabetes over the next six years than those who consumed about 340 mg a day.(2) A study of 43,000 male health professionals turned up similar results.(3)

And last year, the Atherosclerosis Risk in Communities Study (ARIC) weighed in. It has been following about 14,000 middle-aged people for up to seven years.

"We have found that those men and women with the lowest levels of magnesium in their blood at the start of ARIC were twice as likely to be diagnosed later with diabetes as those with the highest levels of magnesium," says Frederick Brancati, an epidemiologist at the Johns Hopkins School of Medicine in Baltimore.(4)

What about people who already have diabetes?

"A high percentage of type 2 diabetics have a deficiency of magnesium inside their cells," says Nadler. But no one knows which came first--the diabetes or the magnesium deficiency.

And it's not clear whether magnesium supplements can help diabetics. Nine small studies have tested 360 mg to 390 mg a day for one to five months. Six found that it didn't lower blood sugar, while three found that it improved insulin sensitivity.

That's what you would expect, says Nadler. "Magnesium is not likely to change blood sugar very much because there are so many factors that influence glucose levels. But it may improve insulin sensitivity," he adds, and that would improve your long-term prospects of avoiding a heart attack or stroke.

High Blood Pressure

Magnesium helps signal muscles to contract and relax. And when the muscles that line the major blood vessels contract, your blood pressure rises.

When researchers studied the diets of 40,000 nurses and 30,000 male health professionals, they found lower blood pressures in people who ate more magnesium.(5,6)

And in the ARIC study, "women with lower levels of magnesium in their blood were more likely to develop high blood pressure over the next few years than women with higher levels," says Aaron Folsom of the University of Minnesota in Minneapolis. That was not true for men, though researchers don't know why.

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

MAGNESIUM - nutritional aspects - includes related articles

Nutrition Action Healthletter, Dec, 1998 by David Schardt

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