Low-magnesium diet may clog heart arteries.

Low-magnesium diet may clog heart arteries

For years, animal studies have suggested that diets low in magnesium -- a mineral typically deficient in the U.S. diet -- may foster atherosclerosis. Now, a rabbit study has identified several physiological changes associated with magnesium deficiency that appear to conspire with cholesterol to promote coronary artery disease.

Epidemiologic studies have indicated that people who drink soft water -- low in minerals such as magnesium and calcium -- average more heart attacks and strokes than those drinking mineral-rich hard water (SN: 9/21/85, p. 187). Hoping to tease out why, Bella and Burton Altura at the State University of New York at Brooklyn and their co-workers focused on rabbits, which are particularly susceptible to artery-clogging atherosclerosis.

One-third of the animals ate standard rabbit chow, another third the same chow laced with 1 percent cholesterol, and the rest chow supplemented with 2 percent cholesterol. In each group, one-third of the rabbits received sufficient magnesium, one-third got only 60 percent of their recommended daily allowance, and the rest got almost three times the recommended daily allowance.

Only rabbits eating cholesteroal developed atherosclerotic damage in the aorta, a major heart artery. The magnesium-deficient animals consistently developed the most and thickest aortic deposits; those on the highest-magnesium diets developed the fewest and thinnest deposits. And for each magnesium category -- low, sufficient or high -- eating more cholesterol resulted in more lesions. Moreover, the researchers report in the March PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES (Vol.87, No.5), atherosclerosis was poorly correlated with serum cholesterol and highly dependent on dietary magnesium.

Only the cholesterol-supplemented animals showed a magnesium-dependent buildup of macrophages, or debrisscavenging white blood cells, in the liver and spleen, the team found. The lower the dietary magnesium, the more macrophages an animal produced. Previous studies have implicated macrophages as a source of the cholesterol-rich "foam cells" associated with atherosclerotic lesions.

The researchers add that "an unexpected and, we believe, significant observation was that animals fed a high-cholesterol diet exhibited an increase in serum magnesium levels, compared to their respective controls, irrespective of the magnesium levels in their diet." They suggest that these "serum concentrations seem to reflect a depletion of tissue magnesium" -- probably a robbing of the mineral from smooth-muscle tissue in blood vessels, Burton Altura says. His previous studies have shown that magnesium is essential to maintaining the integrity of membranes in smooth-muscle cells.

Mildred Seelig, executive director of the American College of Nutrition in Wilmington, N.C., calls the report "a strong paper" and "a very exciting one. Its link between atherosclerosis and lo-magnesium diets confirms scores of studies in other animals and is consistent with observations made in several human studies, she says.

Because researchers often measure magnesium in blood serum, Seelig was intrigued by the possibility that a deficiency might draw magnesium into the serum from stores in the body's soft tissue. This, she says, might explain why many epidemiologic studies fail to find a magnesium deficiency where it might have been expected -- for instance, in people drinking soft water.

James C. Fleet, a nutritional biochemist at the Agriculture Department's Human Nutrition Research Center in Boston, says he finds the study interesting though puzzling. He notes, for example, that when he gives rabbits high-cholesterol diets, they develop "a general sickness," whereas the new report describes the high-cholesterol rabbits as appearing healthy.