Dietary Magnesium Intake in Humans: The Basics
Dietary magnesium in excess is unlikely to reach toxic levels. Known cases of toxicity have occurred in workers inhaling magnesium dust.
Magnesium is an indispensable mineral for the good performance of the organism. It is the second most important cation in cells and acts as a cofactor of enzymes, transporters, and nucleic acids that ensure the normal functioning of various tissues and organs. It participates in the neuromuscular system, in neuronal and muscular excitability; in the cardiovascular system, it acts in the heart and circulation. It also has an antithrombotic effect, stabilizes erythrocytes, and is required for bone growth and maturation, and mineral metabolism.
The total amount of magnesium in an adult person is about 25 g, of which approximately 60% is found in the bones, 39% inside the cells, and 1% in the extracellular fluid. Although its extracellular concentration seems low, it is essential to ensure normal neuromuscular function.
The recommended intake of magnesium is 400-420 mg per day for men and 300-320 mg per day for women. If the recommended amounts are not consumed, a deficiency can occur with health consequences; deficiency can also be caused by low absorption, high intestinal losses, or an imbalance between intestinal absorption and urinary excretion. The absorption of ingested magnesium takes place in the small intestine and under healthy conditions, 45-70% is absorbed, although it can reach up to 90% of the total intake.
The normal blood magnesium level is 1.7 to 2.2 mg/dL and the diagnosis of hypomagnesemia is defined with values below 1.2 mg/dL. Symptoms of deficiency include muscle cramps, convulsions, and tetany, and cardiac alterations, among others. Some causes that lead to magnesium absorption deficiency are high intakes of calcium, phosphate, citrate, fatty acids, phytates, or bile salts. On the contrary, the alteration of the acid-base balance, specifically acidosis, increases its absorption.
Since magnesium participates in enzymatic processes and fulfills structural and regulatory functions, its deficiency significantly affects cardiovascular, renal, gastrointestinal, neurological, and muscular performance. In addition, it induces signs and symptoms related to electrolyte disturbances.
Moderate magnesium deficiency is attributed to very low consumption of leafy greens, milk, bread, and potatoes, among other foods, or by loss of electrolytes. Although severe magnesium deficiency is not common, it is important to point it out as a cause of hypocalcemia with its affectations. Magnesium deficiency in young people causes growth retardation and osteoporosis in older adults. This is easily remedied since the response to magnesium administration is positive and rapid.
Dietary magnesium in excess is unlikely to reach toxic levels. Known cases of toxicity have occurred in workers inhaling magnesium dust.
In general, the consumption of vegetables, especially green leafy vegetables, ensures adequate magnesium intake and, therefore, normal magnesium nutritional status. Under specific conditions, such as pregnancy, advanced age, or in athletes, it can be difficult to cover the daily needs from food; in these situations, the administration of supplements by nutritional or medical recommendation is an option.
Source: Rosa Olivia Méndez Estrada, researcher of the Nutrition Coordination of CIAD.
