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MAGNESIUM
IMPORTANCE:
Magnesium (Mg) is the fourth most abundant mineral 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 plays a key role in at least 300
fundamental enzymatic reactions,(Particularly those that require three B
vitamins (THIAMIN, RIBOFLAVIN and PYRIDOXINE), vitamins C and E. It also helps
fight tooth decay by binding CALCIUM to tooth enamel) 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.
Magnesium is important for such functions as the activation of amino acids, the
aggregation of ribosomes, the binding of RNA to ribosomes and the synthesis and
degradation of DNA. It is essential for the formation of cAMP and other second
messengers and has a key role in neurotransmission and immune function.
Magnesium acts as a calcium antagonist and interacts with other nutrients, such
as potassium and boron.
Magnesium has an important role in regulating the neuromuscular activity of the
heart; maintains normal heart rhythm; necessary for proper calcium & Vitamin C
metabolism; converts blood sugar into energy.
DEFICIENCY SYMPTOMS:
May result in calcium depletion, heart spasms, nervousness, muscular
excitability, confusion; kidney stones, loose teeth.
The
kidneys are extremely efficient in maintaining magnesium homeostasis; therefore,
primary deficiency in healthy individuals is uncommon. Symptomatic deficiency
usually is 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, such as those
requiring ATP and in regulating neurotransmitters. Hypertension, arrhythmia,
neuromuscular manifestations, and personality changes occur during magnesium
deficiency.
Clinical uses:
Magnesium supplementation may be appropriatein acute myocardial infarction,
arrhythmias, cardiac surgery, digitalis toxicity and congestive heart failure.
Magnesium toxicity is rare except in those with impaired kidney function.
Diet
recommendations:
The Recommended Dietary Allowances (RDAs) for Mg are:
|
|
Age (years) |
mg/day |
|
Infants |
0-0.5 |
40 |
|
|
0.5-1.0 |
60 |
|
Children |
1-3 |
80 |
|
|
4-6 |
120 |
|
|
7-10 |
170 |
|
Females |
11-14 |
280 |
|
|
15-18 |
300 |
|
|
19-24 |
280 |
|
|
25-50 |
280 |
|
|
50+ |
280 |
|
Pregnant |
|
320 |
|
Lactating |
1st 6 months |
355 |
|
|
2nd 6 months |
340 |
|
Males |
11-14 |
270 |
|
|
15-18 |
400 |
|
|
19-24 |
350 |
|
|
25-50 |
350 |
|
|
50+ |
350 |
|
1997 RDA FOR MAGNESIUM |
|
babies:
birth to 6 months
6 months to 1 year |
30 mg per day*
75 mg per day*
|
|
children:
1 to 3 years
4 to 8 years
9 to 13 years |
80 mg per day
130 mg per day
240 mg per day
|
|
men and boys:
14 to 18 years
19 to 30 years
31+ years |
410 mg per day
400 mg per day
420 mg per day
|
|
women and girls:
14 to 18 years
19 to 30 years
31+ years |
360 mg per day
310 mg per day
320 mg per day
|
|
pregnant women:
less than 18 years
19 to 30 years
31 to 50 years |
400 mg per day
350 mg per day
360 mg per day
|
|
nursing mothers:
less than 18 years
19 to 30 years
31 to 50 years |
360 mg per day
310 mg per day
320 mg per day
|
Usual
dietary intakes in the U.S. are about 230 and 325 mg/day for women and men,
respectively. Canadian intakes are similar, but the Recommended Nutrient Intakes
(RNIs) are lower (200 and 250 mg/day for adult women and men, respectively).
Food
sources: Good
dietary sources 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 in rats enhances free radical production in skeletal muscle
and oxidation of cholesterol and lipoproteins. Magnesium loss in diabetes may be
due to a renal defect.
For
further information:
Shils,
M.E. (1994) Magnesium. In: Modern Nutrition in Health and Disease (Shils, M.E.,
Olson, J.A. & Shike, M., eds.), 8th ed., pp. 164-184. Lea & Febiger,
Philadelphia, PA.
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