Because magnesium is an intracellular cation, its serum concentrations may not precisely mirror magnesium status. Nonetheless, decreases in serum levels of magnesium indicate a frank deficiency, indicating that serum magnesium concentrations are specific, but not sensitive, to magnesium deficiency. A more state-of-the-art measurement of magnesium status may involve measuring renal magnesium levels, where levels are measured preceding and following the administration of an intravenous magnesium load. If magnesium excretion is reduced over a period of two 24-hour measurements, a deficit exists. In addition, magnesium balance is related to calcium and potassium status, and consequently should be evaluated in combination with these two cations. Despite this knowledge, most researchers still report serum magnesium concentrations to ascertain magnesium deficiency (hypomagnesemia). A comprehensive review of different methods to evaluate magnesium status will not be discussed in this chapter, but will simply be listed. The methods to assess magnesium status are serum magnesium concentrations, plasma ionized magnesium levels, intracellular magnesium concentrations, magnesium balance studies, and the magnesium tolerance test. For further information about these methods, the reader is directed to the Dietary Reference Intakes for Calcium, Phosphorus, Magnesium, Vitamin D, and Fluoride.
Magnesium Requirements
The DRI for magnesium for adults is 310 to 420 mg/day. Intake is often below these recommendations, especially as people age.Table provides a list of some food sources of magnesium. Decreased magnesium intake has been related to an increased risk of metabolic syndrome and type diabetes mellitus. In addition, stressors such as exercise may deplete magnesium, which, together with a sub-optimal dietary magnesium intake, may negatively impact normal metabolism, exacerbate the disease state and impair exercise performance.