Magnesium is the fourth most abundant cation in the body and is second only to potassium within the cell. The adult human body contains 21 to 28 grams of Mg. Of this, 60% is in the bones, 20% in the skeletal muscle, 19% in other cells and about 1% in the extracellular fluid. Magnesium is often the mineral most deficient in modern diets. Mg catalyzes or activates more than 300 enzymes in the body. Low serum magnesium may cause hyperirritability, tetany, convulsions, EKG changes, hypertension, heart attacks, coronary vasospasms and premature atherosclerosis. High serum Mg may occur in dehydration, severe diabetic acidosis, Addison's disease, after a heart attack, in uremia and excessive intake of certain anti-acids. Some sources of Mg are soybeans, shrimp, wheat germ, whole grains, molasses, clams, cornmeal, spinach, oysters, crab, peas, liver, beef, and chlorophyll in the green vegetables. Mg should be taken in a ratio of 2 Mg to 1 Ca. The RDA for Mg is 420 mg/day.