Mg2+ is a vital element in all biologic systems and is the key element in chlorophyll, the first link in the world's food chain. The total body content of Mg 2+ is 24 g, or 2000 meq. Of this, 50 to 70 percent is fixed in bone and is only slowly exchangeable. Most of the remaining Mg 2+ (approximately 40 percent) is found in the ICF space, with a concentration of approximately 40 meq/L. The distribution of Mg2+ is similar to that of potassium, with the major portion intracellular. It is the second most abundant intracellular cation. Serum [Mg2+] ranges between 1.5 and 2.5 meq/L. Mg2+ present in blood is 25 to 35 percent protein-bound, 10 to 15 percent complexed, and 50 to 60 percent ionized. The normal dietary intake of Mg2+ is approximately 20 to 28 meq/day, or 240 to 336 mg/day, and is found in vegetables such as dry beans and leafy greens, meat, and cereals. The majority of Mg2+ is excreted through the gastrointestinal tract in the stool (60 percent) with the remainder (40 percent) in the urine. The kidney is very capable of conserving Mg 2+. A person on an Mg2+-free diet will excrete less than 1 meq/day through the urine. Mg 2+ promotes enzyme reactions within the cell during metabolism, helps in the production of ATP, participates in protein synthesis, and plays a role in coagulation, platelet aggregation, and neuromuscular activity.
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