Magnesium is the fourth most abundant cation (a positively charged ion) 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 has an important role in at least 300 fundamental enzymatic reactions, 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. In addition, it functions in the activation of amino acids and synthesis and degradation of DNA and has a key role in neurotransmission and immune function. Magnesium acts as a calcium antagonist and interacts with nutrients, such as potassium, vitamin B6, and boron.
Magnesium is an essential mineral in humans with a direct involvement in over 300 metabolic reactions. It is necessary for every major biological process, including the production of cellular energy and the synthesis of nucleic acids and proteins. It is also important for the electrical stability of cells, the maintenance of cell membrane integrity, muscle contraction, nerve conduction and the regulation of vascular tone.
Because the kidneys are extremely efficient in maintaining homeostasis of magnesium, a primary deficiency in healthy individuals is uncommon. Symptomatic deficiency is often 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 and in regulating neurotransmitters. Hypertension, arrhythmias, neuromuscular manifestations, and personality changes occur during deficiency.
Accepted clinical uses of magnesium include the treatment of tachycardia and electrolyte depletion. It is also used for the management of premature labor, and for the prophylaxis and treatment of seizures in toxemia of pregnancy and hypomagnesemia associated with such conditions as alcoholism, Crohn’s disease and hyperthyroidism. Magnesium is an active ingredient in antacids and laxatives.
The 1997 Dietary Reference Intakes (DRIs) and the Tolerable Upper Limits (ULs) for magnesium from the Food and Nutrition Board, National Academy of Sciences have been published. The DRIs, according to age and sex, are as follows: Infants 0-6 months, 30 mg and 7-12 months, 75 mg; ages 1-3 years, 80 mg; 4-8 years, 130 mg; 9-13 years, 240 mg; males 14-18 years, 410 mg; males 19-30 years, 400 mg; males >30 years, 420 mg; females 14-18 years, 360 mg; females 19-30 years, 310 mg; and females >30 years, 320 mg. Since no adverse effects from naturally occurring magnesium in foods have been observed, the UL applies only to supplements and magnesium for pharmacological purposes. The ULs are as follows: 1-3 years, 65 mg; 4-8 years, 110 mg; and 9 years and above, 350 mg.
Good dietary sources of magnesium include legumes, whole grain cereals, nuts, dark green vegetables, and cocoa. Hard water and mineral water may be important sources of magnesium.
Magnesium deficiency has been shown to be involved throughout the development of atherosclerosis, including oxidation of cholesterol and lipoproteins and calcification. As a calcium, magnesium supplementation has been shown to exert a cardioprotective effect. Necrotizing enterocolitis, a common cause of death in preterm infants, may be related to magnesium deficiency. Because of its role in neurotransmission, magnesium is being investigated in migraine headaches and attention deficit hypersensitivity disorder.