Major Minerals: Magnesium

Function

Magnesium is involved in over 300 enzymatic reactions, most often in an Mg- ATP complex. Cyclic adenosine monophosphate, a messenger involved in many enzymatic reactions, is activated by magnesium. Magnesium is involved in carbohydrate metabolism, as an activator of enzymes for the initial pathway for glucose oxidation. It serves as a coenzyme in protein synthesis and lipid metabolism, and plays a role in cell reproduction# and growth, and in the action of smooth muscle. /PARAGRAPH HEADING {magabsorb} Absorption and excretion /HEADING PARAGRAPH Magnesium is absorbed in the small intestine; the amount absorbed depends on the magnesium intake of the individual. People on high magnesium diets will absorb only $/frac{1}{4}$ of the magnesium consumed and those on low magnesium diets will absorb approximately $/frac{3}{4}$. Absorption of magnesium is also decreased by a high dietary intake of zinc and possibly fiber. Small amounts of magnesium are excreted in the urine. /PARAGRAPH HEADING {magclin} Clinical conditions /HEADING PARAGRAPH Many conditions can cause magnesium depletion: gastrointestinal disorders with diarrhea and vomiting, renal disorders causing excess losses, alcoholism, endocrine disorders such as hyperthyroidism, and hypermetabolic conditions such as trauma or burns. Low serum levels of magnesium can cause neuromuscular irritability resulting in tremors, spasms, and intensified response to touch and sound. Cardiac arrythmias and abnormal echocardiograms may result. /PARAGRAPH PARAGRAPH Magnesium deficiency can also cause a tetany-like syndrome. Serious metabolic and neurologic disturbances can occur for circumstances in which there is rapid refeeding of protein and carbohydrates without adequate magnesium. /PARAGRAPH HEADING {magintake} Recommended intake /HEADING PARAGRAPH The RDA for magnesium is 420 mg for men and 320 mg for women. Pregnant women require 350-400 mg, and lactating women, 310-360mg. The RDA for infants is 30- 75 mg and for children it ranges from 80 to 240 mg. /PARAGRAPH HEADING {magfood} Food Sources /HEADING PARAGRAPH Magnesium is abundant in many foods, but main sources are nuts, soybeans, cocoa, seafood, whole grains, legumes, and dairy products. /PARAGRAPH FIGURE {magntable} CAPTION Figure %: Magnesium Content of Selected Foods /CAPTION /FIGURE HEADING {magsupp} Supplementation /HEADING PARAGRAPH The recommendation for supplementation usually coincides with the need to maintain recommended dietary intakes. Over supplementation can be dangerous, however: when serum levels of reach 3mEq per liter, magnesium toxicity usually occurs. A decrease in blood pressure is usually the first symptom, with lethargy, confusion, and deterioration in renal function soon following. A serum level of 15 mEq/liter may result in complete heart block and cardiac arrest. /PARAGRAPH