Magnesium is an essential macro mineral that is needed in larger amounts than the trace minerals. Magnesium has important functions in energy production because it stabilises the ATP molecule (as part of the Mg-ATP complex) and is a co‑enzyme in a number of important metabolic pathways including glycolysis, the Krebs cycle and phosphocreatine synthesis. Magnesium serves as a cofactor in over 300 known enzymatic reaction in the catabolism of food for energy. Magnesium is also needed of bone construction and the stabilisation of cell membranes. Magnesium intakes of Western nations is generally below the recommended levels set by government (here), which may in turn be too low for optimum nutrition. Magnesium is known to be necessary for cardiovascular function and deficiency can cause hypertension, electrocardiogram abnormalities as well as impaired carbohydrate metabolism, insulin resistance and decreased insulin secretion.
Because of its functions in energy production and carbohydrate metabolism, magnesium is considered essential in optimal amounts for proper physical performance. Magnesium supplementation may cause increases in strength and improved exercise performance, but it is unclear as to whether these effects are as a result of correction of a deficiency or a pharmacological effect. To test the effect of magnesium on exercise performance researchers1 depleted 10 healthy post menopausal women (47 to 71 y) of magnesium and tested them in submaximal exercise. The subjects consumed 112 mg magnesium/8.4 MJ (2000kcal) with a supplement of 200 mg/d magnesium (as gluconate), followed by a depletion phase with no supplement, and then a repletion phase with the supplement. Red blood cell magnesium concentration, magnesium retention and skeletal muscle magnesium concentration all decreased during the magnesium depletion phase.
While in a state of magnesium depletion, the subjects displayed increased heart rates, an increase in the peak oxygen uptake and an increase in total and cumulative net oxygen utilisation, indicating decreased cardiovascular efficiency during submaximal exercise. These results suggest that magnesium depletion, even if it is mild and of short term, can have a detrimental effect of physical performance. Interestingly there was a correlation between the changes in oxygen uptake and the magnesium losses during the depletion phase, such that those subjects with the most severe magnesium depletion showed a larger deterioration in their physical performance. Optimum magnesium levels would therefore appear to be critical to athletic performance, and so supplementation is recommended because Western diets do not provide adequate levels. Factors such as dietary fibre, calcium, zinc and phytates in foods may reduce the absorption of magnesium, increasing requirement.
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