Chapter 24 - Magnesium Homeostasis

Abstract

Magnesium (Mg) is the fourth most abundant cation and the second most abundant intracellular cation in vertebrates. Mg is involved in numerous biological processes and is essential for life. Mg may be required for enzyme substrate formation. Free Mg2+ also acts as an allosteric activator of numerous enzyme systems, as well as playing a role in ion channels and for membrane stabilization. Mg is therefore critical for a great number of cellular functions, including oxidative phosphorylation, glycolysis, DNA transcription, and protein synthesis. Mg homeostasis is dependent on the amount of Mg ingested, efficiency of Mg intestinal absorption, and renal reabsorption and excretion. The mechanism(s) for intestinal Mg absorption includes passive diffusion and active transport. Mg is absorbed along the entire intestinal tract, including the large and small bowel, but the sites of maximal Mg absorption are the ilium and distal jejunum. Because of the prevalence of Mg in cells and bone, as well as its critical need for numerous biological processes in the body, this mineral plays a profound role in bone and mineral homeostasis. Mg influences the formation and secretion of hormones that regulate skeletal homeostasis and the effect of these hormones on bone. Mg can also directly affect bone cell function as well as influence hydroxyapatite crystal formation and growth. Finally, epidemiological studies have provided a major link associating dietary Mg inadequacy to osteoporosis.