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
