Magnesium is the fourth most abundant cation in the body, with 60% in
the bone and 40% distributed equally between muscle and non-muscular soft
tissue. Only 1% of magnesium is extracellular. Magnesium has an important
role in at least 300 fundamental enzymatic reactions, including the
transfer of phosphate groups, the acylation of coenzyme A in the
initiation of fatty acid oxidation, and the hydrolysis of phosphate and
pyrophosphate. In addition, it functions in the activation of amino acids
and synthesis and degradation of DNA and has a key role in
neurotransmission and immune function. Magnesium acts as a calcium
antagonist and interacts with nutrients, such as potassium, vitamin B6,
and boron.
Deficiencies: Because the kidneys are extremely
efficient in maintaining homeostasis of magnesium, a primary deficiency in
healthy individuals is uncommon. Symptomatic deficiency is often observed
in the presence of a predisposing disease state, such as severe
malabsorption, chronic alcoholism, renal dysfunction, hyperparathyroidism,
or the use of certain medications. Clinical manifestations of deficiency
are related to its role as a cofactor in enzymatic reactions and in
regulating neurotransmitters. Hypertension, arrhythmias, neuromuscular
manifestations, and personality changes occur during deficiency.
Clinical uses: Accepted clinical uses of magnesium
include the treatment of tachycardia and electrolyte depletion. It is also
used for the management of premature labor, and for the prophylaxis and
treatment of seizures in toxemia of pregnancy and hypomagnesemia
associated with such conditions as alcoholism, Crohn's disease and
hyperthyroidism. Magnesium is an active ingredient in antacids and
laxatives.
Diet recommendations: The 1997 Dietary Reference
Intakes (DRIs) and the Tolerable Upper Limits (ULs) for magnesium from the
Food and Nutrition Board, National Academy of Sciences have been
published. The DRIs, according to age and sex, are as follows: Infants 0-6
months, 30 mg and 7-12 months, 75 mg; ages 1-3 years, 80 mg; 4-8 years,
130 mg; 9-13 years, 240 mg; males 14-18 years, 410 mg; males 19-30 years,
400 mg; males >30 years, 420 mg; females 14-18 years, 360 mg; females
19-30 years, 310 mg; and females >30 years, 320 mg. Since no adverse
effects from naturally occurring magnesium in foods have been observed,
the UL applies only to supplements and magnesium for pharmacological
purposes. The ULs are as follows: 1-3 years, 65 mg; 4-8 years, 110 mg; and
9 years and above, 350 mg.
Food sources: Good dietary sources of magnesium
include legumes, whole grain cereals, nuts, dark green vegetables, and
cocoa. Hard water and mineral water may be important sources of magnesium.
Recent research: Magnesium deficiency has been shown
to be involved throughout the development of atherosclerosis, including
oxidation of cholesterol and lipoproteins and calcification. As a calcium
agonist, magnesium supplementation has been shown to exert a
cardioprotective effect. Necrotizing enterocolitis, a common cause of
death in preterm infants, may be related to magnesium deficiency. Because
of its role in neurotransmission, magnesium is being investigated in
migraine headaches and attention deficit hypersensitivity disorder.
