All concepts, explanations, trials, and studies have been
re-written in plain English and may contain errors. I am
not a doctor
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In this review, we tried to clarify the current information
on magnesium's role as a therapeutic agent. A MEDLINE search
from 1966-1999 was done. A total of 51 articles were included
in this review. No animal studies were included.

	Magnesium is a trace mineral involved in more than 300
chemical reactions in the body. Similar to potassium, magnesium
is mainly an intracellular ion. More than two thirds of the
total amount of magnesium is stored in bone, and about 25% in
muscle. About one third of the total amount swallowed can be
absorbed, and the remaining two thirds just passes on through.
	Magnesium absorption depends on your current total
magnesium level. The higher the body stores, the lower the
amount absorbed. Like calcium, magnesium depends on vitamin D
for absorption in the small intestine.
	Magnesium also competes for calcium channels, so it
acts like a calcium channel blocker (an anti-arrhythmic
drug). Magnesium is required for proper functioning of the
sodium pump (1), so when potassium levels do not increase with
supplementation, magnesium deficiency should be suspected.

Magnesium Deficiency

	Less than 1% of the body's magnesium is located outside
cells (in the blood). So blood magnesium levels don't necessarily
relate to total body stores. Current methods of measuring blood
magnesium level and 24-hour urine magnesium loss do not
accurately reflect intracellular magnesium. To figure magnesium
level, kidney function, diuretic use, and dietary intake of
magnesium must be measured to determine the risk of chronic
magnesium deficiency.
	Symptoms of magnesium deficiency generally fall into 4
categories: neuromuscular hypertonicity, psychiatric
disturbances, potassium or calcium problems, or heart effects.
Magnesium supplements may be considered in patients taking
diuretics, patients who are malnourished or alcoholic, patients
with low potassium levels, or those who are diabetic.

Magnesium Excess

	Magnesium excess is rare. It can be dangerous at blood
levels higher than 6 mEq/L. Symptoms include lethargy, nausea
and vomiting, depressed deep tendon reflexes, followed by muscle
paralysis, respiratory depression, and coma. Low blood presssure,
low heart rate, arrhythmia or heart block may occur with
severely high blood magnesium levels of 10-15 mEq/L. Intravenous
calcium may block some of magnesium's effects.

Chronic Respiratory Diseases

	The first modern, controlled study using MgSO4 for
asthma was published in 1987 by Okayama. Treatment resulted
in improvement. McNamara did a study of acute asthma in 38
patients who were randomized to receive either placebo
infusion or intravenous MgSO4. Magnesium therapy resulted in
increased peak flow rate.
	A recent study compared salbutamol inhaler to magnesium
sulfate inhaler. In this randomized double-blind controlled
trial, 33 asthmatic patients were studied. Both groups had
significant increases in peak flow rates - slightly higher in
the magnesium group.
	More recently, people with chronic obstructive pulmonary
disease (COPD) were studied to test magnesium's usefulness. The
trial involved 72 patients who got either standard therapy alone
or standard therapy plus IV magnesium for COPD. Patients had
significantly greater improvements in peak flow than the control
group.

Magnesium and Heart Disease

	Magnesium has become an important treatment option in
managing certain arrhythmias, but its use in the USA remains
limited. LIMIT-2 recruited 2,316 patients with suspected heart
attack and randomized them to receive either IV magnesium or
IV placebo. Mortality at 28 days was 7.8% in the magnesium group
and 10.3% in the placebo group, a relative reduction of 24% in
the magnesium group. Risk of heart failure was also reduced by
25%. Side effects were rare.
	This effect on patients having a heart attack may be due
to a protective effect on the myocardium. Magnesium may help
reform ATP lost during ischemia, thereby helping the heart
recover. Magnesium has been used in heart/lung bypass solutions
for some time for that reason.
	Two other trials provide negative data about magnesium
use in ischemic heart disease. The ISIS-4 trial reported no
benefit for IV magnesium given to 2,000 patients with suspected
heart attack. Low blood pressure was an acute side effect. There
was no effect on mortality.

Congestive Heart Failure

	One study showed lower mortality among CHF patients with
normal blood magnesium levels (71% survival rate), compared to
patients with low magnesium levels (45% survival). However,
patients with high blood magnesium levels had an even lower
survival rate (37%) in the same study.
	IV magnesium has acute effects on the heart's electrical
conduction system but no adverse effects on atrial or ventricular
conduction have been seen.
	Digoxin related arrhythmias respond well to IV magnesium,
even in patients with normal blood magnesium levels. MgSO4 is also
effective for ventricular arrhythmias that do not respond to
lidocaine.
	Along with potassium replacement, magnesium is often
first-line therapy to treat ventricular arrhythmia, especially in
patients taking loop diuretics like Lasix. Magnesium is a
first-line agent for torsades de pointes.

Headaches

	Magnesium may be useful for treating vascular headaches.
Forty-two percent of migraine sufferers had low blood levels of
ionized magnesium.
	Mauskop divided patients who had chronic daily headache
into those with daily migraine headaches (DMH) and those with
daily tension headaches (DTH) and found that 31% of DMH patients
had low blood levels of ionized magnesium. In the DTH group, only
4% had low blood levels of ionized magnesium. Visual disturbances
- thought to be a marker for vascular headaches - may go away
after oral magnesium use.

Title: Magnesium for the Next Millennium
Authors: Randall Swain, Barbara Kaplan-Machlis
Source: South Med J South Med J 92(11), 1999

References:

1) The Na,K-ATPase or sodium pump is a membrane protein that is
helps maintaining the high internal potassium and low internal
sodium levels needed in most animal cells