[Magnesium: metabolism and requirements]

Magnesium is an important element in health and in disease, it is the organism's second most abundant intracellular cation, after potassium, and it is the main divalent intracellular cation. Its metabolic importance is well known, as it has been identified as a cofactor in more than 300 enzymatic reactions which affect the energetic metabolism, and the synthesis of proteins and nucleic acids, Hypomagnesemia is a frequent finding in hospitalized patients, even more so when the patients are critical (+/-65%). Although low serum levels of magnesium imply the presence of intracellular depletion, normal serum magnesium levels may be present in situations of intracellular magnesium depletion, with important clinical repercussions. Keeping in mind that only 1% of the body's magnesium is in the extracellular fluid, the serum magnesium levels may not adequately reflect the situation, which is why techniques have been proposed which determine the intracellular concentración. The identification of the patients who may potentially present a magnesium depletion, requires a clear knowledge of the risk factors associated with magnesium deficiency: poorly controlled diabetes mellitus, excessive alcohol intake, severe diarrhea, important steatorrhea, and the use of drugs which favor their renal excretion. The present review gives an up date of the most frequent causes of magnesium deficits, giving a series of practical recommendations to prevent this situation, and to undertake a correct replacement therapy. Finally, and although hypermagnesemia appears in a reduced number of circumstances, the presence of kidney failure of diverse etiology, as well as the broadening of the indications of magnesium salts, have increased its incidence, which is why special emphasis is made in this section.