Magnesium: A mineral involved in many processes in the body including nerve signaling, the building of healthy bones, and normal muscle contraction. About 350 enzymes are known to depend on magnesium.
Magnesium is contained in all unprocessed foods. High concentrations of magnesium are contained in nuts, unmilled grains, dark-green leafy vegetables, legumes such as peas and beans, and fruit. Magnesium is thus readily available in foods that form the basis of a healthful diet.
Magnesium deficiency can occur due to inadequate intake of magnesium, impaired intestinal absorption of the mineral, or excessive loss of it. Large amounts of magnesium can be lost by prolonged exercise, lactation, excessive sweating and chronic diarrhea; the use of drugs such as diuretics, digitalis, cisplatin and cyclosporine; and kidney disease, an overactive thyroid or parathyroid, low blood levels of potassium (hypokalemia) and high urine levels of calcium (hypercalcemia). Magnesium deficiency is often associated with low blood levels of calcium (hypocalcemia) and potassium (hypokalemia). Deficiency of magnesium causes increased irritability of the nervous system with tetany (spasms of the hands and feet, muscular twitching and cramps, spasm of the larynx, etc.).
According to the National Academy of Sciences, the Recommended Dietary Allowance (RDA) of magnesium is 420 milligrams per day for men and 320 milligrams per day for women. The upper limit of magnesium as supplements is 350 milligrams daily, in addition to the magnesium from food and water. Persons with impaired kidney function should be especially careful about their magnesium intake because they can accumulate magnesium, a dangerous situation.
Drinking water is a significant source of magnesium if the water supply is hard -- rich in minerals. (Water supplies in much of the US are hard but in the Southeast they are soft.) Soft water is deficient in minerals, including magnesium. Water for drinking should therefore not be softened.