Magnesium basics

Abstract

As a cofactor in numerous enzymatic reactions, magnesium fulfils various intracellular physiological functions. Thus, imbalance in magnesium status-primarily hypomagnesaemia as it is seen more often than hypermagnesaemia-might result in unwanted neuromuscular, cardiac or nervous disorders. Measuring total serum magnesium is a feasible and affordable way to monitor changes in magnesium status, although it does not necessarily reflect total body magnesium content. The following review focuses on the natural occurrence of magnesium and its physiological function. The absorption and excretion of magnesium as well as hypo- and hypermagnesaemia will be addressed.

Keywords: hypermagnesaemia; hypomagnesaemia; magnesium; physicochemical properties; physiological function; regulation.

Fig. 1.

(A and B) Magnesium (top left) is surrounded by two hydration shells, whereas calcium (top right) has just one layer. If elements need to fit into a structure (transporter or membrane ‘pore’), calcium (below right) simply sheds its hydration shell and its dehydrated ion will fit. Magnesium (below left), on the other hand, first has to get rid of two layers, which is highly energy consuming (simplified model).

Fig. 2.

Hydroxyapatite crystal unit. Enamel apatite contains the lowest concentrations of carbonate and magnesium ions, and is rich in fluoride F. Dentin and bone have the highest levels of carbonate and magnesium ions, but have low fluoride content. Fluoride decreases solubility and increases chemical stability, carbonate, chloride and especially magnesium all increase solubility of the otherwise very insoluble mineral. Chemically the mineral comprises a highly substituted carbonated calcium hydroxyapatite (HAP). In the absence of exact compositional analysis the biogenic forms of this mineral are collectively alluded to as “bioapatite”. Ca, calcium; Na, sodium; Mg, magnesium; Sr, strontium; OH, hydroxide; Cl, chloride; F, fluoride; PO₄, HPO₄, phosphate; CO₃, carbonate.

Fig. 3.

Total serum magnesium is present in three different states. Because of different measurement methods, results published for each state of serum magnesium vary considerably. Therefore, a range for every state is provided [, , –24]. For additional data, please see also Tables 1 and 2 in the article by Cunningham et al. [28] in this supplement.

Fig. 4.

Magnesium balance. Values as indicated based on [7]. The conversion factor from milligrams to millimole is 0.04113.