Magnesium and Kidney Health - More on the 'Forgotten Electrolyte'.

Whereas in the general population magnesium deficits are most often thought to result mainly in calf cramps (which are generally not considered to be life threatening), it is less well known that a magnesium deficit induced by a magnesium-deficient diet in humans resulted in severe cardiac arrhythmias [5] . Other studies as, for example, an epidemiological study in Germany showed that low serum magnesium levels were associated with higher all-cause and, especially, cardiovascular mortality [6] . A sufficiently high magnesium intake and magnesium status, therefore, seems to be lifesaving. The connection between magnesium and the kidney is manifold. More than being regulated by intestinal absorption, magnesium homeostasis is governed by reabsorption of magnesium from primary urine in the kidney. Of about 2,400 mg magnesium that is being ultra-filtrated daily, 95–99% must be reabsorbed by the nephrons. The mechanisms responsible for the fine-tuning have been elucidated during recent years and primarily involve transport systems located in the thick ascending limb of Henle’s loop and distal convoluted tubules [4] . If the magnesium intake is low, primarily the kidneys avoid rapid and dramatic falls in extracellular magnesium concentrations by increasing the amount of magnesium reabsorption. Therefore, with low magnesium intakes the magnesium concentration in urine is significantly reduced. This is achieved by increased expression and production of magnesium transporters. Magnesium is the fourth most abundant cation and is essential for every cell [1] . This mineral is a cofactor in multiple enzymatic reactions, including those involving energy metabolism as well as DNA and protein synthesis, and it participates in the regulation of ion channels. Magnesium homeostasis is therefore fundamental to the existence of life. However, the clinical significance of magnesium has only been acknowledged during recent years. In fact, years ago, magnesium was even called ‘the forgotten electrolyte’ [2] . In this issue of the American Journal of Nephrology, Rebholz et al. [3] report on the correlation between dietary magnesium intake and kidney function decline from a large epidemiological investigation, the HANDLS study. Compared with the upper tertile of dietary magnesium intake, the risk for rapid kidney function decline was roughly doubled in the lower tertile. This result adds to a growing number of epidemiological studies connecting increased risk for various diseases with a low dietary magnesium intake or low serum magnesium concentration. Up to now, these correlations were reported for diabetes type 2, stroke, cardiovascular diseases and even sudden cardiac death (reviewed in [4] ). The relevance of these findings is important as the general magnesium intake in the western population is low. Dietary data suggest that the average magnesium intake has declined markedly over the last 100 years. Studies in the US showed that 23.5% of the population had a daily dietary magnesium intake of less than 50% of the recommendations. Similar trends to low dietary magnesium intake were found in UK and Germany. The daily magnesium intakes below recommendations increased from 25% of the total population to about 50%. Published online: October 22, 2016 Nephrology American Journal of