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Good Nutrition Nutrition

Nutrition Notes Topics

Magnesium (Mg)

Magnesium is a critical ion, regulating nerve and muscle cell function. It also is a co-factor for many enzymes of the energy extraction system, and protein synthesis pathways. The adult RDA is 300-350 mg/day. It is actively and passively absorbed. If active transport fails, dietary requirements rise sharply, analogous to calcium absorption problems. Magnesium is widely distributed in plant and animal foods, so that deficiency usually only occurs with impaired absorption, malnutrition, alcoholism, or diuretic use.

Deficiency symptoms begin with nausea, loss of appetite, edema, fatigue, and progress to major neurological symptoms- tremors, disordered movement, convulsions, and coma. Magnesium and calcium deficiency may predispose to sudden death from cardiac arrhythmia, and ironically, is most likely to occur with diet and diuretic therapies for hypertension and heart disease.

Mg deficiency may contribute to increased bone loss; hypocalcemia is associated with low magnesium due to impaired parathyroid hormone secretion or resistance to PTH action. Serum concentrations of vitamin D are also low.

Magnesium deficiency also occurs in chronic alcoholism from Mg loss in the urine, exacerbated by low dietary intake, gastrointestinal losses with diarrhea or vomiting. Osteoporosis is prevalent in the alcoholic population. Low magnesium in alcoholics may also contribute to increased cardiovascular disease by enhanced platelet aggregation which can be corrected with Mg therapy. Mg inhibits the synthesis of thromboxane A2 and 12-hydroxyeicosatetraenoic acid, eicosanoids thought to be involved in platelet aggregation. Mg also inhibits the thrombin-induced Ca2+ influx in platelets, as well as stimulates synthesis of prostaglandin I2, a potent anti-aggregatory eicosanoid.

Baragallo et al suggested that reduced intracellular Mg concentrations may explain the association between diabetes 2 and hypertension. Insulin regulates the shift of Mg from extracellular to intracellular spaces and in turn intracellular Mg concentration modulates insulin action. Low intracellular Mg concentrations are found in diabetes 2 and in hypertensive patients. Daily Mg administration restores the intracellular Mg concentration and contributes to improve insulin-mediated glucose uptake.

Magnesium supplementation should be considered for every patient on diuretics, and patients with cardiovascular disease - hypertension and increased risk of heart attacks. Magnesium replacement is essential for alcoholics and increased doses are given during withdrawal from alcoholic beverage intake. Magnesium supplements in the range of 5 mg/kg/day or 300-500 mg/day for the average adult may be desirable.