Magnesium Metabolism and its Disorders, Prof R Swaminathan, Clin Biochem Rev. 2003 (full paper!)
Abstract
Magnesium is the fourth most abundant cation in the body and plays an important physiological role in many of its functions. Magnesium balance is maintained by renal regulation of magnesium reabsorption. The exact mechanism of the renal regulation is not fully understood. Magnesium deficiency is a common problem in hospital patients, with a prevalence of about 10%. There are no readily available and easy methods to assess magnesium status. Serum magnesium and the magnesium tolerance test are the most widely used. Measurement of ionised magnesium may become more widely available with the availability of ion selective electrodes.
Magnesium deficiency and hypomagnesaemia can result from a variety of causes including gastrointestinal and renal losses. Magnesium deficiency can cause a wide variety of features including hypocalcaemia, hypokalaemia and cardiac and neurological manifestations. Chronic low magnesium state has been associated with a number of chronic diseases including diabetes, hypertension, coronary heart disease, and osteoporosis. The use of magnesium as a therapeutic agent in asthma, myocardial infarction, and pre-eclampsia is also discussed.
Hypermagnesaemia is less frequent than hypomagnesaemia and results from failure of excretion or increased intake. Hypermagnesaemia can lead to hypotension and other cardiovascular effects as well as neuromuscular manifestations. Causes and management of hypermagnesaemia are discussed.
“....Neuromuscular and Central Nervous System Manifestations
The earliest manifestations of magnesium deficiency are usually neuromuscular and neuropsychiatric disturbances. The most common clinical manifestations are hyperexcitability, including positive Chvostek's and Trousseau's signs, tremor, fasciculations and tetany. Frank tetany in magnesium deficiency is usually associated with hypocalcaemia. There may be several mechanisms contributing to the wide variety of neuromuscular problems in magnesium deficiency. Magnesium is required for stabilisation of the axon. The threshold for axon stimulation is decreased and nerve conduction velocity increased when serum magnesium concentration is low. By competitively inhibiting the entry of calcium into pre-synaptic nerve terminals, magnesium influences the release of neurotransmitters at the neuromuscular junction and causes hyper-responsive neuromuscular activity.52 Magnesium also influences muscle contraction and relaxation by its effect on calcium handling by the muscle cell. In the muscle cell, the sarcoplasmic reticulum regulates the contraction/relaxation cycle by releasing and reactivating calcium. In magnesium deficiency, the release of calcium from the sarcoplasmic reticulum is increased. In addition, magnesium is required for the re-uptake of calcium. The net effect on the muscle of a low intracellular magnesium concentration is increased contractility to a given stimulus and reduced ability to recover from the contraction, making it prone to tetany.
The effect of magnesium deficiency on the central nervous system is even more complicated and less well understood. Magnesium deficiency seems to cause an intracellular calcium overload and disturbances in its subcellular distribution. Magnesium deficiency is associated with stimulation of excitatory neurotransmitters such as serotonin and acetylcholine, non-competitive blockade of the N-methyl-D-aspartate receptor and possibly inhibition of action of the inhibitory amino acid ?-amino butyric acid.3
...Magnesium Deficiency, Hypertension and Vascular Tone
There is an inverse relationship between magnesium intake and blood pressure and epidemiological studies show an increased incidence of hypertension in areas where the magnesium content of water is low.11 Furthermore, magnesium supplementation was associated with a significant decrease in blood pressure in 10 out of 15 studies.21 In-vitro and in-vivo studies show that magnesium can influence vascular tone and reactivity. Magnesium deficiency increases angiotensin II induced plasma aldosterone concentration and production of thromboxane and vasoconstrictor prostaglandins.87 Insulin resistance caused by magnesium deficiency also increases vascular tone. Changes in cytosolic free calcium produced by magnesium deficiency may increase vascular reactivity even further. Magnesium supplementation can reduce the pressor effect of angiotensin II and stimulate the production of the vasodilator prostaglandin I2.11 Magnesium may also influence the release of nitric oxide and its effects on vascular tone.83...”
...Miscellaneous Conditions
Chronic fatigue syndrome, characterised by flu-like symptoms that are followed by months or years of disabling lethargy as well as mood alterations, has been linked with low magnesium status. However, not all studies have shown evidence of low magnesium status in this syndrome.52 Sudden deaths in athletes have been attributed to magnesium deficiency. As magnesium is important for the supply and utilisation of energy rich compounds, concern has been expressed that exercise-induced magnesium deficiency may impair athletic performance.52 Magnesium deficiency is also thought to contribute to increased susceptibility to infections and migraine.52
learn more/full paper:
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1855626/