Magnesium and Heart Health

Magnesium appears to be essential for the integrity of the heart muscle.

Only within the last 35 years has there been any recognition of the importance of magnesium in health and disease. As recently as 1952, the following statement concerning magnesium was made in a popular textbook of metabolism: "Little is known as yet of its function in the human organism and of the relation of disturbances of magnesium metabolism to clinically observable abnormalities in man." We now know that magnesium is a vital element in many body systems, especially those involving enzymes; it is, in fact, an essential co-factor in more than 300 enzyme systems, especially those involved in reactions that require phosphates for energy. It is also necessary for basic physiologic processes such as the function of DNA, the transmission of nerve impulses and the contraction of skeletal and heart muscle. Since magnesium helps maintain the integrity and strength of the skeleton, deficits are accompanied by a variety of structural and functional disturbances.

Magnesium is ubiquitous in its distribution throughout the body. It is second only to potassium as the most abundant positive ion within the cell and is present to some degree in all organs and tissues. Magnesium must be balanced with calcium, sodium and potassium for the proper regulation of nerve impulse transmission and muscle contraction.

The Recommended Dietary Allowance (RDA) for magnesium is 350 milligrams (mg) for men and 300 mg for women. This recommendation increases to 450 mg during pregnancy and lactation. These amounts appear to be adequate for normal individuals but may be inadequate for people on restrictive diets or those with serious defects in the intestinal absorption of magnesium or in its reabsorption by the kidney. The level of magnesium in the blood can be readily measured. The correlation between blood levels and the more important tissue levels, however, is not consistent, and a false impression of body magnesium content may be obtained by relying only on blood levels.

The average mixed American diet supplies about 120 mg of magnesium per 1,000 calories. Green leafy vegetables are particularly good sources of the mineral, as are dry beans and peas, soybeans, nuts and whole grains. High losses of magnesium occur in the refinement of foods, and some losses result when cooking water is discarded.

Magnesium deficiency is more common than you migh expect; surveys indicate that approximately 10 percent of "normal" individuals have less than normal blood levels of magnesium. E.B. Flink, author of "Magnesium Deficiency in Human Subjects: A Personal Historical Perspective," has listed numerous causes of magnesium deficiency. He classifies them into nutritional causes (dietary insufficiency, alcoholism); intestinal causes (diarrhea, malabsorption); excess loss of magnesium through the kidneys (due to disease or the influence of drugs, especially diuretics); endocrine and metabolism causes (hyperthyroidism, pregnancy, excessive lactation, high levels of serum calcium); and genetic and neonatal causes.

Clinically, magnesium deficiency may be present in a variety of ways. Symptoms related to the central nervous system are the most obvious but require a relatively severe deficiency before they make themselves known. When present, they may include personality changes, muscle spasms, tremors, numbness and tingling and in extreme instances, convulsions and delirium.

Recent evidence suggests that most common manifestations of hypomagnesemia involve the cardiovascular system. They are, however, almost always attributed to existent disease of the heart or to complications related to potassium deficiency. Hypomagnesemia may occur secondary to increased urinary loss of magnesium associated with the use of diuretics. A decrease in the heart muscle content of magnesium may occur secondary to coronary artery disease and heart attacks due to coronary thrombosis. Magnesium appears to be essential for the maintenance of the functional integrity of the heart muscle and magnesium deficiencies have been linked to abnormal heart rhythms and to sudden death. Supplemental magnesium has been shown to be effective in preventing abnormalities in heart rhythm that are associated with heart attacks and digitalis intoxication. Evidence shows that magnesium also helps maintain the health of arterial walls and that a deficiency of the mineral may predispose to the development of arteriosclerosis and hypertension.

The absorption of orally administered magnesium is unpredictable, but 45 percent is the usual estimate. Both magnesium hydroxide and magnesium oxide are capable of raising serum magnesium levels when administered orally alone or as food supplementation.

Supplemental magnesium is well tolerated and excess magnesium is rarely a problem, essentially occurring only in the presence of severe kidney disease and the inability of the body to excrete magnesium.