Magnesium (Mg) is the fourth most abundant mineral in the body and the most abundant intracellular divalent cation, with essential roles in many physiological functions. Consequently, the assessment of Mg status is important for the study of diseases associated with chronic deficiency. In spite of intense research activities there is still no simple, rapid, and accurate laboratory test to determine total body Mg status in humans. However, serum Mg ,0·75 mmol/l is a useful measurement for severe deficiency, and for values between 0·75 and 0·85 mmol/l a loading test can identify deficient subjects. The loading test seems to be the gold standard for Mg status, but is unsuitable in patients with disturbed kidney and intestinal functions when administered orally. There is also a need to reach a consensus on a standardized protocol in order to compare results obtained in different clinical units. Other cellular Mg measurements, such as total or ionized Mg, frequently disagree and more research and systematic evaluations are needed. Muscle Mg appears to be a good marker, but biopsies limit its usefulness, as is the case with bone Mg, the most important but heterogeneous Mg compartment. The development of new and non invasive techniques such as nuclear magnetic resonance (NMR) may provide valuable tools for routinely analysing ionized Mg in tissues. With the development of molecular genetics techniques, the recent discovery of Transient Receptor Potential Melastatin channels offers new possibilities for the sensitive and rapid evaluation of Mg status in humans.Loading test: Serum: Erythrocyte: Lymphocytes: Muscle: Bone: Ionized Mg Magnesium (Mg) is the fourth most abundant mineral in the body, and the most abundant intracellular divalent cation, and is essential for a diverse range of physiological functions. Mg deficiency, either from inadequate intake, excess excretion or altered homeostasis, is often suspected to be associated with the initiation of many symptoms and diseases (1) . In spite of its multiple and ubiquitous roles, Mg status can be assessed in severe deficiency and a large number of studies have investigated various markers during nutritionally induced or pathological mild and chronic deficiency. A review published in 1991 stated that the assessment of Mg status was difficult as there was no simple, rapid and accurate test to indicate total body Mg status (2) . More recently, another review indicated that whilst functional and/or biological markers are available for many nutrients, there is still a need for indicators to specifically diagnose Mg deficiency (3) . Another difficulty associated with Mg is related to its metabolism. It is known that the equilibrium and exchange of Mg between body compartments and tissue pools occurs slowly, so determining Mg concentration in one tissue may not provide information about Mg status in another. This review provides the most up-to-date information on the assessment of Mg status.
MetabolismThe metabolism of Mg and its body distribution have been investigated in an...