Magnesium: An Essential Mineral

Article by Don Goldberg

Facts About Magnesium

Magnesium: What is it?
Magnesium is a mineral needed by every cell of your body. About half of your body’s magnesium stores are found inside cells of body tissues and organs, and half are combined with calcium and phosphorus in bone. Only 1 percent of the magnesium in your body is found in blood. Your body works very hard to keep blood levels of magnesium constant (1).
Magnesium is needed for more than 300 biochemical reactions in the body. It helps maintain normal muscle and nerve function, keeps heart rhythm steady, and bones strong. It is also involved in energy metabolism and protein synthesis (2).
What foods provide magnesium?
Green vegetables such as spinach provide magnesium because the center of the chlorophyll molecule contains magnesium. Nuts, seeds, and some whole grains are also good sources of magnesium (3).
Although magnesium is present in many foods, it usually occurs in small amounts. 
As with most nutrients, daily needs for magnesium cannot be met from a single food. Eating a wide variety of foods, including five servings of fruits and vegetables daily and plenty of whole grains, helps to ensure an adequate intake of magnesium.
The magnesium content of refined foods is usually low (4). Whole-wheat bread, for example, has twice as much magnesium as white bread because the magnesium-rich germ and bran are removed when white flour is processed. The table of food sources of magnesium suggests many dietary sources of magnesium.
Water can provide magnesium, but the amount varies according to the water supply. “Hard” water contains more magnesium than “soft” water. Dietary surveys do not estimate magnesium intake from water, which may lead to underestimating total magnesium intake and its variability (4).
What is the Recommended Dietary Allowance for Magnesium?
The Recommended Dietary Allowance (RDA) is the average daily dietary intake level that is sufficient to meet the nutrient requirements of nearly all (97-98 percent) individuals in each life-stage and gender group (4). The 1999 RDAs for magnesium for adults (4), in milligrams (mg), are:(in the following order: Men, Women, Pregnancy, Lactation)
Ages 14 to 18: 410 mg, 360 mg, 400 mg, and 360 mg
Ages 19 to 30: 400 mg, 310 mg, 350 mg, and 310 mg
Ages 31 and over: 420 mg, 320 mg, 360 mg, and 320 mg
Results of two national surveys, the National Health and Nutrition Examination Survey (NHANES III-1988-91) (5) and the Continuing Survey of Food Intakes of Individuals (1994 CSFII) (4), indicated that the diets of most adult men and women do not provide the recommended amounts of magnesium. The surveys also suggested that adults age 70 and over eat less magnesium than younger adults, and that non-Hispanic black subjects consumed less magnesium than either non-Hispanic white or Hispanic subjects (4).
When can Magnesium deficiency occur?
Even though dietary surveys suggest that many Americans do not consume magnesium in recommended amounts, magnesium deficiency is rarely seen in the United States in adults. When magnesium deficiency does occur, it is usually due to excessive loss of magnesium in urine, gastrointestinal system disorders that cause a loss of magnesium or limit magnesium absorption, or a chronically low intake of magnesium (4, 6-9).
Treatment with diuretics (water pills), some antibiotics, and some medicine used to treat cancer, such as Cisplatin, can increase the loss of magnesium in urine (4, 10). Poorly controlled diabetes increases loss of magnesium in urine, causing a depletion of magnesium stores (6). Alcohol also increases excretion of magnesium in urine, and a high alcohol intake has been associated with magnesium deficiency (11, 12).
Gastrointestinal problems, such as malabsorption disorders, can cause magnesium depletion by preventing the body from using the magnesium in