Magnesium is a very important essential macromineral, even though there are only several ounces in the body (0.05 percent of body weight). It is involved in several hundred enzymatic reactions, many of which contribute to production of energy and cardiovascular function. The great amount of research on magnesium done in the last decade has resulted in major changes in our knowledge. Decreases in magnesium intake have been more prevalent in our American diet with additions of supplemental vitamin D and calcium, dietary phosphorus, and refined or processed carbohydrate foods. Drinking soft water decreases magnesium intake, while diuretic drugs cause magnesium loss, as do alcohol, caffeine, and sugar. Decreased blood and tissue levels of magnesium have been shown to be related to high blood pressure, kidney stones, heart disease and, particularly, heart attacks due to coronary artery spasm (magnesium helps relax and dilate coronary arteries). Studies have indicated that a decreased concentration of magnesium is found in the heart and blood of heart attack victims, though it is not clear whether this is a cause or a result of the problem. Magnesium's role in alleviating premenstrual syndrome (PMS) has made big news as well.
Magnesium, like calcium, is an earth alkali mineral. The word magnesium comes from the name of the Greek city, Magnesia, where large deposits of magnesium carbonate (MgCO3) were found. This "salt" was first used as a laxative; magnesium carbonate and magnesium sulfate are still used in this way. Magnesium is the "iron" of the plant world-as iron is to hemoglobin, magnesium is to chlorophyll, the "blood" pigment of plants. The central atom of the chlorophyll structure is magnesium.
About 65 percent of our magnesium is contained in the bones and teeth. As with calcium, the bones act as a reservoir for magnesium in times of need. The remaining 35 percent of magnesium is contained in the blood, fluids, and other tissues; there is a high concentration, actually higher than in the blood, in the brain. Magnesium is present in significant amounts in the heart Most of it, like potassium, is inside the cells.
The process of digestion and absorption of magnesium is very similar to that of calcium. The suggested ratio of intake of these two vital nutrients is about 2:1, calcium to magnesium. Magnesium also requires an acidic stomach environment for best absorption, so taking it between meals or at bedtime is recommended. Meals high in protein or fat, a diet high in phosphorus or calcium (calcium and magnesium can compete), or alcohol use may decrease magnesium absorption. It is possible that some of the hangover symptoms related to alcohol are in part due to magnesium depletion. Taking this mineral with some thiamine (B1) and drinking extra water can help prevent hangover symptoms.
Usually, about 40-50 percent of the magnesium we consume is absorbed, though this may vary from 25-75 percent depending on stomach acid levels, body needs, and dietary habits. Stress may increase magnesium excretion, and the resulting temporary magnesium depletion may make the heart more sensitive to electrical abnormalities and vascular spasm that could lead to cardiac ischemia. The kidneys can excrete or conserve magnesium according to body needs. The intestines can also eliminate excess magnesium in the feces. Otherwise, magnesium absorption is generally affected by the factors shown in the table (see Calcium) entitled Factors Affecting Calcium Absorption.