When given orally, magnesium sulfate (Epsom salts) is not absorbed but attracts water into the colon and thus acts as an effective laxative. Epsom salts in a bath are absorbed slightly and are known to be relaxing. For injuries, a concentrated solution is used as a compress to help drain toxins. Magnesium is also thought to reduce lead toxicity and its buildup, possibly through competing for absorption. Since magnesium is an alkaline mineral, it is used in several over-the-counter antacids.

Deficiency and toxicity: Toxicity due to magnesium overload is almost unknown in a nutritional context, as excesses are usually eliminated in the urine and feces. However, symptoms of magnesium toxicity can occur more likely if calcium intake is low. These symptoms may include depression of the central nervous system, causing muscle weakness, fatigue, sleepiness, or even hyperexcitability. In extreme states, magnesium overload can cause death.

Magnesium deficiency is actually fairly common; however, it is usually not looked for, and therefore, not found or corrected. Deficiency is more likely in those who eat a processed-food diet; in people who cook or boil all foods, especially vegetables; in those who drink soft water; in alcoholics; and in people who eat food grown in magnesium-deficient soil, where synthetic fertilizers containing no magnesium are often used. Deficiency is also more common when magnesium absorption is decreased, such as after burns, serious injuries, or surgery and in patients with diabetes, liver disease, or malabsorption problems; and when magnesium elimination is increased, as in people who use alcohol, caffeine, or excess sugar, or who take diuretics or birth control pills.

Early symptoms of magnesium deficiency can include fatigue, anorexia, irritability, insomnia, and muscle tremors or twitching. Psychological changes, such as apathy, apprehension, decreased learning ability, confusion, and poor memory may occur. Tachycardia (rapid heartbeat) and other cardiovascular changes are likely with moderate deficiency, while severe magnesium deficiency may lead to numbness, tingling, and tetany (sustained contraction) of the muscles as well as delirium and hallucinations.

Arterial spasm, specifically of the coronary arteries, is a significant recent concern with magnesium deficiency. This could lead to angina symptoms or even a heart attack. Blood pressure can rise with magnesium deficiency, while an increased likelihood of kidney stones and other tissue calcification is possible.

Requirements:The current Recommended Daily Allowance (RDA) is about 300-350 mg. for adults-350 mg. for men and 300 mg. for women, increasing to about 450 mg. during pregnancy and lactation. The minimum is also expressed as about 6 mg. per kg. (2.2 pounds) of body weight. Many authorities feel that the RDA should be doubled, to about 600-700 mg. daily. An average diet usually supplies about 120 mg. of magnesium per 1,000 calories, for an estimated daily intake of about 250 mg. Unless absorption is great, that is not going to produce adequate tissue levels of magnesium for most people.

Magnesium chelated with amino acids is probably the most absorbable form. Less absorbable forms include magnesium bicarbonate, magnesium oxide, and magnesium carbonate. Magnesium oxide is probably somewhat better than magnesium carbonate (dolomite). The newly available salts of magnesium aspartate or citrate, both known as mineral transporters, have a better percentage of absorption.