Magnesium in the Body

The body of an average 70 kg adult contains about 2,000 mEq (equivalent to 1 mol or 24.305 g) of magnesium, about 50% of which is stored in the bones, 45% existing as intracellular cations, and about 5% in the extracellular fluid (Klein et al. 1997; Caddell 1974; Harris and Wilkinson 1971). Magnesium is one of the most abundant cations in the intracellular fluids in the body (Fox et al. 2007). The level of Mg in the extracellular fluid ranges between 0.7 and

1.05 mmol/L, where homeostasis is maintained by the kidneys and intestine (Okuma 2001). Hence, Mg is an important component of human physiology. However, at serum Mg levels exceeding 1.05 mmol/L, it is known to lead to muscular paralysis, hypotension, and respiratory distress (Vormann 2003), and cardiac arrest occurs for severely high serum levels of 6-7 mmol/L. Nevertheless, the incidence of hyper-Mg is rare due to the efficient excretion in the urine (Vormann 2003; Saris et al. 2000).

Mg is one of the essential minerals besides calcium required for bone and tooth formation (Okuma 2001; Nielsen 2006; Kobayashi et al. 2002; Toba et al. 2000; Wang et al. 1994). Mg ions are essential for many enzyme activities in carbohydrates, proteins, metabolism of nucleic acids and the interaction of intracellular particles and binding of macromolecules to subcellular organelles, such as the binding of messenger ribonucleic acid (RNA) to ribosomes. Mg, a co-factor for many enzymes, is known to stabilize the structures of DNA and RNA (Saris et al. 2000). Mg ions bind to ATP and play important roles in neurochemical transmission, muscular activity, nerve conduction, and signaling (Altura and Altura 1996) (http://

Absorption of magnesium occurs in the upper small bowel by means of an active process closely related to the transport system for calcium. Magnesium is excreted mainly by the kidney. Renal excretion of magnesium increases during diuresis induced by ammonium chloride, glucose, and organic mercurials. Magnesium affects the central nervous, neuromuscular, and cardiovascular systems. Insufficient magnesium (hypomagnesemia) in the extracellular fluid increases the release of acetylcholine and can cause changes in cardiac and skeletal muscle. Some of the conditions that can produce hypomagnesemia are diarrhea, steatorrhea, chronic alcoholism, and diabetes mellitus. Hypomagnesemia may occur in newborns and infants who are fed cow's milk or artificial formulas, apparently because of the high phosphate/magnesium ratio in such diets. Hypomagnesemia is often treated with parenteral fluids containing magnesium sulfate or magnesium chloride. Excess magnesium (hypermagnesemia) in the body can slow the heartbeat, and concentrations greater than 15 mEq/L can produce cardiac arrest in diastole. Excess magnesium also causes vasodilation by direct effects on the blood vessels and by ganglionic blockade. Hypermagnesemia is usually caused by renal insufficiency and is manifested by hypotension, electro-cardiographic changes, muscle weakness, sedation, and a confused mental state (Navarro-González 1998).

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